9th Physics Short Questions ( English Medium)

9th PHYSICS
Short question answers.
All questions from textbook are answered. All the questions from BISE Lahore
PHYSICS paper from 2013-18 are answered with suitable picture diagrams.
2018
Ayub‫حمزه‬
STARS ACADEMY Shahdara Town Lahore.
8/14/2018
ExerciseExerciseExerciseExercise
ShortShortShortShort
QuestionsQuestionsQuestionsQuestions
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nit 01
PHYSICAL QUANTITIES ANDPHYSICAL QUANTITIES ANDPHYSICAL QUANTITIES ANDPHYSICAL QUANTITIES AND
MEASUREMENTMEASUREMENTMEASUREMENTMEASUREMENT
1.2 What is difference between base and derived quantities? Give 3 examples in each
case. [L.B. 2015,16,17]
Base Quantities:
“Base quantities are the quantities on the
basis of which other quantities are
expressed.”
Examples; Length, mass and time are base
quantities.
Derived Quantities:
“The quantities that are expressed in terms
of base quantities are called derived
quantities.”
Examples; Volume, speed and force are
derived quantities.
1.3 Pick out the base units in the following; joule, Newton, kilogram, hertz, mole,
ampere, meter, Kelvin, coulomb and watt.
Base Units: Kilogram, mole, ampere, meter and Kelvin.
Derived Units: Joule, Newton, hertz, coulomb and watt.
1.4 Find the base quantities involved in the following derived quantities:
a) speed b) volume c) Force d) work
a) Speed: Speed is derived from length and time.
b) Volume: Volume is derived from length.
c) Force: Speed is derived from mass, length and time.
d) Work: Speed is derived from mass, length and time.
1.5 Estimate your age in seconds. [L.B. 2014,15,17,18]
Age in Seconds: ˭˳ I˧˥ = ˳˥IJJ = 15 × 1 ˳˥IJJ
˭˳ I˧˥ = 15 × 365 ˤI˳J = 15 × 365 × 1 ˤI˳
˭˳ I˧˥ = 15 × 365 × 24 ℎJ˯JJ = 15 × 365 × 24 × 1 ℎJ˯J
˭˳ I˧˥ = 15 × 365 × 24 × 60 ˭˩J˯ˮ˥J = 15 × 365 × 24 × 60 × 1 ˭˩J˯ˮ˥J
˭˳ I˧˥ = 15 × 365 × 24 × 60 × 60 J˥IJJˤJ = 15 × 31536000 J
˭˳ I˧˥ = ˳˥IJJ = 473040000 J
U

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1.6 What role SI units have played in development of science? [L.B. 2016]
Importance of SI: System international has fulfilled the need of a commonly acceptable
worldwide system of units for science and technology.
1.7 What is meant by Vernier constant? [L.B. 2014,15,17**]
Vernier Constant: “The minimum measurement that can be taken by vernier callipers is
called least count of vernier callipers or vernier constant.”
Value: Vernier constant = 0.1 mm = 0.01 cm
1.8 What do you understand by zero error of a measuring instrument? [L.B. 2014]
Zero Error: “The extent of error in any measuring instrument is called zero error of that
instrument.”
Types: Zero error may be Positive or Negative.
1.9 Why is the use of zero error necessary in a measuring instrument?
Use of zero error: Use of zero error ensures the precision and accuracy of measurement
taken by the measuring instrument.
1.10 What is a stop watch? What is the least count of mechanical stop watch you have
used in laboratories?
Stop Watch: “A stop watch is used to measure time interval of an event.”
Least Count of Mechanical Stop Watch = 0.1 s
Least Count of Digital Stop Watch = 0.01 s
1.11 Why do you need to measure extremely small interval of times?
Measuring Interval of Time: Different physical quantities like displacement, velocity and
acceleration, power and momentum are related to time. So we need to measure extremely
small intervals of time to get more precise readings.
1.12 What is meant by significant figures of a measurement?
Significant Figures: “All the accurately known digits and first doubtful digit in an expression
are called significant figures.”
1.13 How is precision related to significant figures in a measuring quantity?
Precision & Sig. Figs.: Number of significant figures reflects the precision of a measured
value of a physical quantity.

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IMPORTANT SHORT QUESTIONS FROM BISE LAHORE
01010101 Define physics. [L.B. 2014,15]
Physics: “Physics is the branch of science in which we study matter, energy and their
interactions.”
Mechanics, optics, sound and electromagnetism are few branches of physics.
02020202 Define plasma physics, geo physics and nuclear physics. [L.B. 2016,17,18]
Plasma Physics: “Plasma physics is the study of production and properties of ionic state of
matter – fourth state of matter.”
Nuclear Physics: Nuclear Physics is the study of properties and behavior of nuclei and
particles within the nuclei.”
Geo Physics: “Geo physics is the study of internal structure of earth.”
00003333 How many divisions are present on vernier scale? [L.B. 2016]
No. of Divisions: 10 divisions are present on vernier scale of vernier callipers.
04040404 What is meant by prefixes? Give example. [L.B. 2016]
Prefixes: “Prefixes are the words or letters added before SI units. These are multiples of
10.”
Examples: Common examples of prefixes are kilo (k = 103
), milli (m = 10-3
), centi (c = 10-2
)
etc.
00005555 Write 2 rules to find significant figures in a measurement. [L.B. 2016]
Rules: 1. Digits other than zero are significant.
2. Zero between significant digits is also significant.
00006666 Write the names of 2 length measuring instruments. [L.B. 2017]
Instruments: Two common length measuring instruments are metre rule and measuring
tape.
07070707 What do you mean by scientific notation? Give one example. [L.B. 2018]
Scientific notation: “A way to express a given number as a number between 1 and 10
multiplied by 10 having an appropriate power is called scientific notation or standard form.”

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nit 02
KINEMATICSKINEMATICSKINEMATICSKINEMATICS
2.2 Explain translatory motion and give examples of various types of translator motion.
[L.B. 2016,17]
Translatory Motion: “In translational motion, a body moves along a line without any
rotation. The line may be straight or curved.”
Types: There are 3 types of translatory motion.
1. Linear motion: A car moving in a straight line and objects falling downward have linear
motion.
2. Circular motion: A bicycle moving on a circular track possesses circular motion. Motion of
moon around earth is circular motion.
3. Random motion: The motion of insects is random motion. The motion of dust particles in
air is also random motion.
2.3 Differentiate between the following;
(1) Rest and Motion
Rest: “A body is said to be at rest, if it does
not change its position with respect to its
surroundings.”
Motion: “A body is said to be in motion, if it
changes its position with respect to its
surroundings.”
Example: A passenger sitting inside a moving bus is at rest with respect to other passengers
but to another observer outside the bus passenger inside the bus is in motion.
(2) Circular motion and rotatory motion
Circular Motion: “The motion of an object in
circular path is called circular motion.”
Example: Motion of earth around sun.
Rotatory Motion: “The spinning motion of
an object about its axis is called its rotatory
motion.”
Example: Motion of earth about its own axis.
(3) Distance and displacement [L.B. 2016,17]
Distance: “Length of a path between two
points is called distance between those
points.”
Quantity: Distance is a scalar quantity.
Displacement: “Displacement is the shortest
distance between two points which has
magnitude and direction.”
Quantity: Displacement is a vector quantity.
U

(4) Speed and velocity
Speed: “The distance covered by an object in
unit time is called its speed.”
Quantity: Speed is a scalar quantity.
(5) Linear and random motion
Linear Motion: “Straight line
body is called linear motion.”
Example: A car moving in a straight line and
objects falling downward have linear
motion.
(6) Scalars and vectors
Scalars: “A scalar quantity is described
completely by its magnitude only
Example: Distance, time, speed
2.4 Define the terms speed, velocity and acceleration.
Speed: “The distance covered by an object in
Velocity: “The rate of displacement
Acceleration: “Acceleration is defined as the rate of change
2.5 Can a body moving at constant speed have acceleration?
Body with Constant Speed: Yes
have acceleration if it is moving in circular path
2.6 How riders in Ferris wheel possess
motion?
Motion of Riders: The motion of riders is;
Translatory because they move in circular path
Not rotatory because the axis of rotation is not passing through the wheel.
2.7 Sketch a distance-time graph for a body starting from rest. How will you determine the
speed of a body from this graph?
Graph: Distance-time graph is shown.
speed of object. Consider points A & B on the graph.
JJ˥˥ˤ J˦ JI˪˥Iˮ = JˬJJ˥ J˦
JJ˥˥ˤ J˦ JI˪˥Iˮ =
˖˩JˮIJI˥
ˮ˩˭˥
hamzaa
: “The distance covered by an object in
quantity.
Velocity: “The rate of displ
body is called velocity.”
Quantity: Velocity is a vector
Linear and random motion
motion of a
A car moving in a straight line and
objects falling downward have linear
Random Motion: “The disordered or
irregular motion of an object is called
random motion.”
Example: The motion of insects
motion. The motion of dust particles in air is
also random motion.
[L.B. 2014
described
magnitude only.”
Distance, time, speed etc.
Vectors: “A vector quantity is described
completely by it magnitude and direction
Example: Force, displacement, velocity
Define the terms speed, velocity and acceleration.
The distance covered by an object in unit time is called its speed.”
The rate of displacement of a body is called velocity.”
Acceleration is defined as the rate of change of velocity of a body.”
Can a body moving at constant speed have acceleration? [L.B. 2014
Yes! The body moving with constant speed may
moving in circular path.
wheel possess translator motion but not rotator
: The motion of riders is;
because they move in circular path without rotation.
time graph for a body starting from rest. How will you determine the
speed of a body from this graph?
time graph is shown. Its slope gives the
of object. Consider points A & B on the graph.
ˬ˩J˥ ˓˔
˖˩JˮIJI˥
ˮ˩˭˥
=
20 ˭
2 J
= 10 ˭J #
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[L.B. 2014,15]
: “The rate of displacement of a
vector quantity.
[L.B. 2014]
The disordered or
of an object is called
The motion of insects is random
motion. The motion of dust particles in air is
2014,15**,17**]
A vector quantity is described
magnitude and direction.”
: Force, displacement, velocity etc.
[L.B. 2015**,17]
unit time is called its speed.”
of velocity of a body.”
2014]
constant speed may
translator motion but not rotator
time graph for a body starting from rest. How will you determine the

2.8 What would be the shape of a velocity
moving with variable speed?
v-t Graph: Velocity-time graph of a body moving with variable speed
is shown.
2.9 Which of the following can be obtained from speed
graph of a body; (1) Initial speed (2) Final speed (3) Distance covered in time
Acceleration of motion.
Speed-Time Graph: All of the above quantities can be find by v
in straight line.
2.10 How can vector quantities be represented graphically?
Graphical Representation: To
Draw a straight line (length of line is
Put an arrowhead at on end (to
2.11 Why vector quantities cannot be added and subtracted like scalar quantities?
Vector Addition: Vectors cannot be added like scalars
addition, direction is also added.
2.12 How are vector quantities important to us in our daily life?
Importance: Vector quantities are
Locating exact position of objects.
Indicating direction of motion of object.
Drawing maps.
2.14 Sketch a velocity-time graph for the motion of the body. From the graph explaining
each step, calculate total distance covered by the body
Velocity-Time graph: (2nd
Equation of motion.)
00001111 Convert speed of 20 ms-1
˟J˥˥ˤ
˟J˥˥ˤ
hamzaa
What would be the shape of a velocity-time graph of a body
[L.B. 2014,15]
time graph of a body moving with variable speed
Which of the following can be obtained from speed-time
of a body; (1) Initial speed (2) Final speed (3) Distance covered in time
of the above quantities can be find by v-t graph if the body is moving
How can vector quantities be represented graphically?
To represent a vector graphically:
Draw a straight line (length of line is magnitude of vector).
at on end (to signify direction).
Why vector quantities cannot be added and subtracted like scalar quantities?
: Vectors cannot be added like scalars due to their direction
addition, direction is also added.
How are vector quantities important to us in our daily life?
: Vector quantities are important to us in
Locating exact position of objects.
Indicating direction of motion of object.
time graph for the motion of the body. From the graph explaining
each step, calculate total distance covered by the body.
Equation of motion.)
1
into kmh-1
.
˟J˥˥ˤ = 20 ˭J #
= 20 ×
3600 × 10%
10% × 3600
˭J #
=
20 × 3600
10%
×
10%
˭
3600 J
=
72000
1000
×
˫˭
ℎ
˟J˥˥ˤ = 72 Š #
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of a body; (1) Initial speed (2) Final speed (3) Distance covered in time t (4)
t graph if the body is moving
[L.B. 2014]
Why vector quantities cannot be added and subtracted like scalar quantities?
direction. During vector
[L.B. 2016]
time graph for the motion of the body. From the graph explaining
[L.B. 2016]

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02020202 Define uniform speed. [L.B. 2016]
Uniform Speed: “A body has uniform speed if it covers equal distance in equal intervals of
time however short the interval may be.”
03030303 What is meant by gravitational acceleration? [L.B. 2016]
Gravitational Acceleration: “The acceleration of freely falling objects is called gravitational
acceleration.”
Value: The value of gravitational acceleration g on the surface of earth is 10 ms-2
.
04040404 Define uniform acceleration. [L.B. 2016,17]
Uniform Acceleration: “A body has uniform acceleration if it has equal changes in velocity in
equal intervals of time however short the interval may be.”
05050505 Define vibratory motion. [L.B. 2017]
Vibratory Motion: “To and fro motion of a body about its mean position is called vibratory
motion.”
Example: Motion of pendulum and motion of child sitting on sea saw is vibratory motion.
06060606 Define acceleration and write its unit. [L.B. 2018]
Acceleration: “Acceleration is defined as the rate of change of velocity of a body.”
Unit: SI unit of acceleration is ms-2
.
nit 03
DYNAMICSDYNAMICSDYNAMICSDYNAMICS
3.2 Define the following terms;
(1) Inertia [L.B. 2015,16]
Inertia: “Inertia of a body is its property due to which it resists any change in its state of rest
or motion.”
Dependence: Inertia of a body depends upon its mass.
U

(2) Momentum
Momentum: “Momentum of a body is the
and velocity.”
Formula:
Unit: SI unit of moment is kgms
(3) Force
Force: “A force moves or tend
force can also change the direction of motion of a body.
Unit: Unit of force is Newton (
(4) Force of friction
Friction: “The force that opposes the motion
Friction depends upon nature
(5) Centripetal force.
Centripetal Force: “Centripetal force is a force that
Formula:
3.3 What is the difference between;
(1) Mass and weight
Mass: “Mass is the amount of matter
substance.”
Quantity: Mass is a scalar quantity
(2) Action and reaction
Action and Reaction: If “The force that
is referred as action.” Then “The upward force
referred as reaction.”
(3) Sliding and rolling friction.
Sliding Friction: “The force of
by a surface when it slides over other
Note: Rolling friction is 100 times
hamzaa
Momentum of a body is the quantity of motion it possesses due to its mass
˜zȎ = ˭˜zȎ
kgms-1
.
A force moves or tends to move, stops or tends to stop the motion of a body. The
force can also change the direction of motion of a body.”
: Unit of force is Newton (N).
opposes the motion of a moving object is called friction.”
nature of surface, contact area and pressing force.
[L.B.
Centripetal force is a force that keeps a body to move
ͨ͹ =
ͽY
΂
What is the difference between;
amount of matter in any
quantity.
Weight: “Weight is the force of gravitation
acting on an object.”
Quantity: Weight is a vector
force that book applies on the table downward
referred as action.” Then “The upward force by the table on book will be
.
e of friction faced
over other.”
Rolling Friction: “The force of
by a surface when it rolls over other
times less than sliding friction.
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[L.B. 2014,15]
it possesses due to its mass
[L.B. 2016]
to stop the motion of a body. The
of a moving object is called friction.”
[L.B. 2015,16,17]
a body to move in circle.”
[L.B. 2014,15**]
force of gravitation
vector quantity.
book applies on the table downward
by the table on book will be
The force of friction faced
over other.”

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3.4 What is the law of inertia? OR State Newton’s 1st
law of motion. [L.B. 2014,16,18]
Law of Inertia: Newton’s first law of motion is also called as law of inertia.
Statement: “A body continues its state of rest or uniform motion in a straight line provided
no net force acts on it.”
3.5 Why is it dangerous to travel on the roof of a bus?
Travel on the Roof: The passengers traveling on the roof of bus are always in a danger to
fall in front of bus.
Reason: When brakes are applied, the passengers continue their straight line motion due to
inertia.
3.6 Why does a passengers move outward when a bus takes a turn?
Passengers Move Outward: When a bus takes a sharp turn, passengers continue their
straight line motion due to inertia. So they feel moving outward from the bus.
3.7 How can you relate a force with the change of momentum of a body?
Force and Momentum: “When a force acts on a body, it produces acceleration in the body
and will be equal to the rate of change of momentum of the body.”
Mathematical Form: ͨ =
W W
Y
3.8 What will be the tension in the rope that is pulled from its ends by two opposite forces
100 N each?
Tension: The tension in the string is equal to the force acting on either side of string. So the
tension will be 100 N.
3.9 Action and reaction are always equal and opposite. Then how does a body move?
Action and Reaction: Action and reaction act on different bodies. Forces of action and
reaction produce acceleration in different bodies and cannot nullify the effect of each
other.
3.10 A horse pulls the cart. If action and reaction are equal and opposite the how does
the cart move?
Horse-Cart: Action and reaction act on different bodies. Forces of horse and cart produce
acceleration in different bodies and cannot nullify the effect of each other. Hence the cart
moves.

3.11 What is the law of conservation of momentum?
Law of Conservation of Momentum
than two interacting bodies remains constant
3.12 Why is the law of conservation of momentum important?
Importance: Law of conservation of momentum is important in order to understand
The movement of system of gun bullet
The rocket and jet engine.
Almost all isolated systems.
3.13 When a gun is fired, it recoils. Why?
Gun Recoils: The gun recoils to
gun and bullet are at rest, so the total momentum of system is zero. The bullet gets
momentum when fired, so the gun recoils in opposite direction.
3.14 Describe two conditions in which force of friction is needed.
Need of Friction: To walk or to run friction is needed to push the ground backward.
is highly desirable when climbing up a hill
3.15 How does oiling the parts of a machine lower
Oiling: Due to oiling parts of machine become
other becomes easy. Hence friction is lessened.
3.16 Describe ways to reduce friction.
Reducing Friction: The friction can be reduced by
Making sliding surfaces smooth
Making fast moving objects
Lubricating the sliding surfaces
Using ball bearings or roller bearings
3.17 Why rolling friction is less than sliding friction?
Rolling Friction: During rolling motion contact
minimum and rolling surface rolls without rupturing the
cold welds which makes rolling friction about
than sliding friction.
3.18 What do you know about the following;
hamzaa
What is the law of conservation of momentum?
Law of Conservation of Momentum: “The momentum of an isolated system of two or more
remains constant.”
Why is the law of conservation of momentum important?
Law of conservation of momentum is important in order to understand
system of gun bullet.
The rocket and jet engine.
When a gun is fired, it recoils. Why?
The gun recoils to conserve the momentum of system. Before firing, both the
momentum when fired, so the gun recoils in opposite direction.
Describe two conditions in which force of friction is needed.
or to run friction is needed to push the ground backward.
climbing up a hill.
ng the parts of a machine lower friction?
of machine become smooth the movement of one surface over
other becomes easy. Hence friction is lessened.
Describe ways to reduce friction.
: The friction can be reduced by
surfaces smooth
Making fast moving objects streamlined shape
the sliding surfaces
roller bearings.
Why rolling friction is less than sliding friction?
g motion contact area is
and rolling surface rolls without rupturing the
cold welds which makes rolling friction about 100 times less
What do you know about the following;
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system of two or more
Law of conservation of momentum is important in order to understand
[L.B. 2018]
Before firing, both the
[L.B. 2017]
or to run friction is needed to push the ground backward. Friction
the movement of one surface over
[L.B. 2014]
[L.B. 2014,18]

(1) Tension in a string
Tension: “The force acting along a
(2) Limiting Force of Friction: “
between two static surfaces in contact with each other is referred as limiting force of
friction.”
(3) Braking Force: “A sufficient amount of friction must be generated between tyres of
vehicle and surface of track which
(4) Skidding of Vehicle: “If brakes are applied too strongly, the tyres of vehicle will lock up
(stop turning) and will slip on the track. This
(5) Seatbelts: Seatbelts secure
collision. When brakes are applied the person inside the vehicle continues his motion due to
inertia and may collide with windscreen or any other thing.
(6) Banking of Roads: “Banking of road means
Advantage: Banking causes a component of vehicle’s
provide necessary centripetal
of road prevents skidding of vehicle and thus make
(7) Cream separator: Cream separator is a high speed
control the fat contents of various products.
Principle of Working: Cream separator works on the same principle of
The high speed spinning bowl causes the heavier contents of m
bowl and lighter contents move in centre where it is collected through pipe.
3.19 What would happen if all friction suddenly disappears?
Friction Disappears: If all friction disappears we will not able to move on earth, it
difficult to stop any moving object, birds will not be able to fly etc.
3.20 Why the spinner of washing machine is made to spin at high speed?
Spinner: When spinner is rotated at high speed, the
forced out through holes of container due to
IMPORTANT SHORT QUESTIONS FROM BISE LAHOREIMPORTANT SHORT QUESTIONS FROM BISE LAHOREIMPORTANT SHORT QUESTIONS FROM BISE LAHOREIMPORTANT SHORT QUESTIONS FROM BISE LAHORE
01010101 What is meant by centrifugal force?
Centrifugal Force: “The opposite
Direction: The direction of centrifugal force is
hamzaa
acting along a stretched string is called as tension.”
: “The maximum amount of friction that can be generated
in contact with each other is referred as limiting force of
A sufficient amount of friction must be generated between tyres of
vehicle and surface of track which can stop the vehicle, this friction is called braking force.”
“If brakes are applied too strongly, the tyres of vehicle will lock up
on the track. This slipping is called skidding of vehicle.”
secure the person sitting in fast moving vehicle from harmful
inertia and may collide with windscreen or any other thing.
: “Banking of road means that outer edge of road is raised
Banking causes a component of vehicle’s weight to
centripetal force while taking a turn. Thus banking
of vehicle and thus makes the driving safe.
Cream separator is a high speed spinner used to
control the fat contents of various products.
: Cream separator works on the same principle of centrifuge
The high speed spinning bowl causes the heavier contents of milk to move outward in the
What would happen if all friction suddenly disappears?
: If all friction disappears we will not able to move on earth, it
difficult to stop any moving object, birds will not be able to fly etc.
Why the spinner of washing machine is made to spin at high speed?
When spinner is rotated at high speed, the water droplets from wet clothes are
ugh holes of container due to lack of centripetal force.
What is meant by centrifugal force? [L.B. 2014]
The opposite reaction of centripetal force is called centrifugal force.”
: The direction of centrifugal force is outward from the centre of circle.
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that can be generated
in contact with each other is referred as limiting force of
A sufficient amount of friction must be generated between tyres of
is called braking force.”
“If brakes are applied too strongly, the tyres of vehicle will lock up
is called skidding of vehicle.”
the person sitting in fast moving vehicle from harmful
raised.”
centrifuge machine.
ilk to move outward in the
: If all friction disappears we will not able to move on earth, it will be
Why the spinner of washing machine is made to spin at high speed?
droplets from wet clothes are
is called centrifugal force.”
from the centre of circle.

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02020202 The weight of a body is 147 N. What is its mass? [L.B. 2015]
˱˥˩˧ℎˮ = ˱ = ˭˧ = 147 ˚
∴ ˭IJJ = ͽ =
Y
X
=
147
10
˭IJJ = ˭ = 14.7 ˫˧
04040404 Define the SI unit of force. [L.B. 2017]
Unit of Force: SI unit of force is kgms-2
which is equal to Newton (N).
Newton: “One newton (1N) is the force that can produce an acceleration of 1 ms-2
in a body
of mass 1 kg.” 1 ˚ = 1 ˫˧ × 1 ˭J $
05050505 State Newton’s 3rd
law of motion. [L.B. 2017]
Newton’s 3rd
Law of Motion: “To every action there is an equal but opposite reaction.”
Example: When the fuel of rocket burns, hot gases escape out from tail with high speed. The
reaction of these gases on the rocket causes it to move opposite to gases rushing out
of its tail.
nit 04
TURNING EFFECT OF FORCETURNING EFFECT OF FORCETURNING EFFECT OF FORCETURNING EFFECT OF FORCE
4.2 Define the following;
(1) Resultant vector
Resultant Vector: “Such a vector, which shows the combined effect of two or more vectors
is called resultant vector.”
NOTE: Two or more vectors are added to find resultant vector by head to tail rule.
(2) Torque
Torque: “The turning effect of a force is called torque or moment of force.”
Dependence: Torque depends on force ∝ ͨ and Torque also depends on moment arm
∝ ͮ
Formula: = ͨ × ͮ
U

(3) Centre of mass
Centre of Mass: “Centre of mass of a system is such a
the system to move without rotation
(4) Centre of gravity.
Centre of Gravity: “A point where the
downward is called centre of gravity
4.3 Differentiate the following;
(1) Like and unlike forces
Like Parallel Forces: “Like parallel forces are
the forces that are parallel to each other and
have same direction.”
Example: Weights of apples in a bag are
vertically downward. These are like parallel
forces.
(2) Torque and couple
Torque: ““The turning effect of a force is
called torque or moment of force.”
Torque is produced by a single force or by a
combination of forces.
(3) Stable and neutral equilibrium.
Stable Equilibrium: “A body is said to be in
stable equilibrium if after a slight tilt it
returns to its previous position.”
Position of C.G.: In stable equilibrium centre
of gravity is at lowest position
4.4 How head to tail rule helps to find the resultant of forces?
Head to Tail Rule: Head to tail rule is graphical method to find resultant of 2 or more than 2
vectors.
Description: Consider any of the
and the other as 2nd
. Draw the vectors
that tail of the 2nd
vector coincides with the head of 1
Similarly draw the next vector (if any).
(resultant vector) such that its tail is at the tail of 1
last vector.
hamzaa
[L.B.
Centre of mass of a system is such a point where an applied
move without rotation.”
[L.B.
where the whole weight of the body appears to act vertically
downward is called centre of gravity of a body.”
Differentiate the following;
[L.B.
Like parallel forces are
to each other and
: Weights of apples in a bag are
vertically downward. These are like parallel
Unlike Parallel Forces: “Unlike parallel
forces are the forces that are
have opposite direction to each other.”
Example: Weight of apple,
string, and tension in string vertically upward
are unlike parallel forces.
of a force is
called torque or moment of force.”
Torque is produced by a single force or by a
Couple: “A couple is formed by
parallel forces of the same magnitude but
not along the same line.
Couple is a combination of unlike parallel
forces which produces torque.
Stable and neutral equilibrium.
A body is said to be in
stable equilibrium if after a slight tilt it
to its previous position.”
In stable equilibrium centre
lowest position.
Neutral Equilibrium: “A body is said to be in
neutral equilibrium if after a slight tilt it
remains in its new position
Position of C.G.: In neutral equilibrium
centre of gravity remains in the
position irrespective to its new position.
ail rule helps to find the resultant of forces?
Head to tail rule is graphical method to find resultant of 2 or more than 2
Consider any of the vectors zzȎ and zzȎ as 1st
vector
Draw the vectors zzȎ and zzȎ graphically such
vector coincides with the head of 1st
vector.
Similarly draw the next vector (if any). Now draw the vector ʼzzȎ
(resultant vector) such that its tail is at the tail of 1st
vector while its head is at the head of
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[L.B. 2014,15,17]
where an applied force causes
[L.B. 2014**,16**]
of the body appears to act vertically
[L.B. 2014,15**,17]
: “Unlike parallel
s are the forces that are parallel but
to each other.”
, suspended by
and tension in string vertically upward
[L.B. 2016]
A couple is formed by two unlike
of the same magnitude but
Couple is a combination of unlike parallel
forces which produces torque.
: “A body is said to be in
neutral equilibrium if after a slight tilt it
new position.”
In neutral equilibrium
centre of gravity remains in the same
irrespective to its new position.
Head to tail rule is graphical method to find resultant of 2 or more than 2
vector while its head is at the head of

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4.6 When a body is said to be in equilibrium? [L.B. 2015,16]
According to 1st
condition: “A body is said to be in equilibrium if resultant of all forces
acting on it is zero.”
According to 2nd
condition: “A body is said to be in equilibrium if resultant of all torques
acting on it is zero.”
So, a body is in equilibrium if it satisfies either both or any one condition for equilibrium.
4.7 Explain the first condition for equilibrium.
First Condition: “A body is said to satisfy 1st
condition for equilibrium if resultant of all
forces acting on it is zero.” ͨ =
Example: A book lying on the table or a picture hanging on the wall satisfy the 1st
condition
for equilibrium.
4.8 Why there is a need of second condition for equilibrium if a body satisfies first
condition for equilibrium?
Need of 2nd
Condition: Only the 1st
condition for equilibrium does not ensure that a body is
in equilibrium as in the figure (a) resultant of F1 and F2 is zero (1st
condition is satisfied).
When location of F1 and F2 is shifted as in figure (b), the body has tendency to rotate. So
body is not in equilibrium.
4.9 What is second condition for equilibrium? [L.B. 2016,18]
Second Condition: “A body is said to satisfy 2nd
condition for equilibrium if resultant of all
torques acting on it is zero.” =
Example: A ladder leaning at a wall satisfies the 2nd
condition for equilibrium.
4.10 Give an example of a moving body which is in equilibrium.
Example: Any object moving in straight line with uniform velocity is in equilibrium. A
paratrooper coming down with terminal velocity (constant velocity) also satisfies 1st
condition for equilibrium.
4.11 Think of a body which is at rest but not in equilibrium. [L.B. 2016]
Body at Rest: In ideal situation, two forces act on a body thrown vertically upward. One is
the applied force vertically upward and other is weight vertically downward. At peak point,
body is at rest and applied force is zero but weight acts on body. Hence body is not in
equilibrium in presence of single force.
F1
F2
F1
F2

4.12 Why a body cannot be in equilibrium due to single force acting on it?
Single Force: Because single force cannot make resultant force to be zero.
not in equilibrium.
4.13 Why the height of vehicles is kept as low as possible?
Height of Vehicles: The height of vehicles is kept low to
possible which makes the equilibrium of vehicle
4.13 Explain what is meant by stable, unstable and neutral
in each case.
Stable Equilibrium: “A body is said to be in stable equilibrium if after a slight tilt it
returns to its previous position.”
Example: When we slightly tilt a book lying on table by lifting it from opposite side
it returns to previous position. This state of book is stable equilibrium.
Unstable Equilibrium: “A body is said to be in unstable equilibrium if after a
slight tilt it does not return to its previous position.”
Example: A pencil balanced on its tip is i
Neutral Equilibrium: “A body is said to be in
tilt it remains in its new position
Example: A ball is in neutral equilibrium because it always remains in new displaced
position.
IMPORTANTIMPORTANTIMPORTANTIMPORTANT
00001111 Define perpendicular components
Perpendicular Components: “
to each other are called perpendicular components.”
00002222 In a right angled triangle length of base is 4 cm and its perpendicular is 3 cm. Find
length of hypotenuse.
˔IJ˥ = 4 I˭
By Pythagorean Theorem {
{H˳J
hamzaa
Why a body cannot be in equilibrium due to single force acting on it?
Because single force cannot make resultant force to be zero.
vehicles is kept as low as possible?
: The height of vehicles is kept low to make centre of gravity
possible which makes the equilibrium of vehicle more stable.
what is meant by stable, unstable and neutral equilibrium. Give an example
: “A body is said to be in stable equilibrium if after a slight tilt it
When we slightly tilt a book lying on table by lifting it from opposite side
it returns to previous position. This state of book is stable equilibrium.
: “A body is said to be in unstable equilibrium if after a
on its tip is in unstable equilibrium.
: “A body is said to be in neutral equilibrium if after a slight
position.”
A ball is in neutral equilibrium because it always remains in new displaced
IMPORTANTIMPORTANTIMPORTANTIMPORTANT SHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORE
perpendicular components.
: “The components of a force which are mutually perpendicular
are called perpendicular components.”
In a right angled triangle length of base is 4 cm and its perpendicular is 3 cm. Find
I˭ ˜˥JJ˥Jˤ˩I˯ˬIJ = 3 I˭ H˳JJˮ˩J˯J˥ =
{H˳J. {$
= {˔IJ˥{$
- {˜˥JJ. {$
{H˳J. {$
= {4{$
- {3. {$
= 16 - %
{H˳J. {$ = 25 = 5
H˳JJˮ˩J˯J˥ = 5 I˭
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Why a body cannot be in equilibrium due to single force acting on it? [L.B. 2015]
Because single force cannot make resultant force to be zero. Hence the body is
f gravity as lower as
equilibrium. Give an example
: “A body is said to be in stable equilibrium if after a slight tilt it
When we slightly tilt a book lying on table by lifting it from opposite side,
: “A body is said to be in unstable equilibrium if after a
equilibrium if after a slight
A ball is in neutral equilibrium because it always remains in new displaced
SHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORESHORT QUESTIONS FROM BISE LAHORE
[L.B. 2014]
The components of a force which are mutually perpendicular
In a right angled triangle length of base is 4 cm and its perpendicular is 3 cm. Find
[L.B. 2014]

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00003333 Define moment arm, rigid body and axis of rotation? [L.B. 2014,15,16,17]
Moment Arm: “The perpendicular distance between axis of rotation and the line of action
of force is called moment arm.”
Rigid Body: “If the distance between particles of a body remains unchanged, the body will
be called as rigid body.”
04040404 Write the mathematical form of conditions of equilibrium. [L.B. 2017]
1st
Condition for Equilibrium: ͨ =
2nd
Condition for Equilibrium: =
00005555 What is meant by resolution of forces? [L.B. 2017**]
Resolution of Force: “Splitting up of a force in 2 mutually perpendicular components is
called resolution of force.”
06060606 Define resolution of forces. [L.B. 2018]
Resolution of Forces: “Splitting up of a force into perpendicular components is called
resolution of forces.”
The perpendicular components are ͨY = ͨFˍG , ͨY = ͨ ΃X;
nit 05
GRAVITATIONGRAVITATIONGRAVITATIONGRAVITATION
5.2 What is meant by the force of gravitation? [L.B. 2015**,16**,17]
Force of Gravitation: “The force due to which every body of the universe attracts every
other body.”
Formula: ˙JI˰˩ˮIˮ˩JIJˬ ˘JJI˥ ∝ JJJˤ˯Iˮ J˦ ˭IJJ˥J & ˙JI˰˩ˮIˮ˩JJIˬ ˘JJI˥ ∝
#
˙JI˰˩ˮIˮ˩JJIˬ ˘JJI˥ = ͨ =
ͩ ͽ ͽ
X
U

P a g e | 17
5.3 Do you attract the earth or the earth attracts you? Which one is attracting with a
larger force? You or the earth.
By Gravitation Law: “Everybody in the universe attracts every other body with a force which
is directly proportional to the product of their masses and inversely proportional to the
square of distance between their centres.”
Thus, we and earth all attract each other with a mutual (same) force.
5.4 What is a field force? [L.B. 2018]
Field Force: “Field force is such a force which one body can apply on other weather the
body is in contact with it or not.”
Example: Gravitational force is an example of field force.
5.5 Why earlier scientists could not guess about gravitational force? [L.B. 2017]
Guess about Gravitational Force: Due to very small value of G, the gravitational force of
attraction between objects around us is very small. That is why earlier scientists could not
guess it.
5.6 How can you say that gravitational force is a field force?
Gravitational Field Force: The velocity of a body, thrown up, goes on decreasing while on
returns its velocity goes on increasing. The earth’s gravitational force produces acceleration
in the body weather the body is in contact with earth or not. So earth’s gravitational force is
a field force.
5.7 Explain, what is meant by gravitational field strength? [L.B. 2014,15,18]
Gravitational Field Strength: “In the gravitational field of earth, the gravitational force per
unit mass is called the gravitational field strength of the earth.”
Value: On the surface of earth value of gravitational field strength is 10 N kg-1
.
5.8 Why is law of gravitation important to us?
Importance: Gravitation law is important for us because we can use it;
To calculate gravitational force of attraction between objects
To calculate the mass of Earth and other solar planets
To understand the orbital motion of natural and artificial satellites.

P a g e | 18
5.9 Explain the law of gravitation. [L.B. 2014,17**,18]
Gravitation Law: “Everybody in the universe attracts every other body with a force which is
directly proportional to the product of their masses and inversely proportional to the square
of distance between their centres.”
Mathematical Form: ˙JI˰˩ˮIˮ˩JJIˬ ˘JJI˥ = ͨ =
ͩ ͽ ͽ
X
5.10 How can the mass of earth be determined?
Mass of Earth: Mass of earth can be calculated by gravitation law.
ͯX =
XW
ͩ
= 6.0 × 10$&
˫˧
Here, ͯX = ˭IJJ J˦ ˗IJˮℎ, X = ˧JI˰˩ˮIˮ˩JJIˬ III˥ˬ˥JIˮ˩JJ, W = JIˤ˩˯J J˦ ˗IJˮℎ, ͩ = ˙JI˰˩ˮIˮ˩JJ IJJJˮIJˮ
5.11 Can you determine the mass of moon? If yes then what do you need to know?
Mass of Moon: Yes! Mass of moon can be determined by the following formula;
ͯͽ =
Xͽ{Wͽ{
ͩ
= 7.35 × 10$$
˫˧
Here, ͯX = ˭IJJ J˦ ˭JJJ, X = ˧JI˰˩ˮIˮ˩JJIˬ III˥ˬ˥JIˮ˩JJ ˦JJ ˭JJJ,
Wͽ = JIˤ˩˯J J˦ ˭JJJ, ͩ = ˙JI˰˩ˮIˮ˩JJ IJJJˮIJˮ
5.12 Why does the value of g vary from place to place? [L.B. 2016]
Value of g: As by formula, X =
{ {
X ∝
#
{ {
∴ gh is inversely proportional to
{˞ - ℎ{$
So value of gh varies with height and is different on different places.
5.13 Explain how value of g varies with altitude?
Value of g: As by formula, X = { {
X ∝
#
{ {
∴ gh is inversely proportional to {˞ - ℎ{$
At a height equal to one earth radius above earth surface g becomes one fourth of its value
and so on.

5.14 What are artificial satellites?
Artificial Satellites: “Scientists have sent many
revolve around earth. These are called artificial satellites.”
Use: Most of the artificial satellites orbiting the earth are used for
5.15 How Newton’s law of gravitation helps in understanding the motion of satellites?
Understanding the Motion of Satellites
move around the earth. The gravitational force of attraction between earth and satellite
provides the necessary centripetal force. So Newton’s law of gravitation is important to
understand the motion of satellites.
5.16 On what factors the orbital speed of a satellite depends?
Factors: By formula;
Here, ͲͿ = JJI˩ˮIˬ ˰˥ˬJI˩ˮ˳, X
΂Ϳ = JIˤ˩˯J J˦ JJI˩ˮ
So, orbital speed of satellite depends on
΂Ϳ{JIˤ˩˯J J˦ JJI˩ˮ = ˞Iˤ˩˯J J˦
5.17 Why communication satellites are stationed at
geostationary orbits?
Satellites in Geostationary Orbits
stationed at geostationary orbits so that signal transmission
could face no problem.
Explanation: Communication satellites take
around earth. As earth also completes its one rotation about its own axis in
they appear to be stationary. Hence they face no problem in signal transmission.
IMPORTANT SHORIMPORTANT SHORIMPORTANT SHORIMPORTANT SHOR
01010101 Describe navigation system.
Navigation System: GPS (Global Positioning System) is a satellite navigation system. It helps
us to find exact position of object anywhere on land, on sea and in air.
GPS consists of 24 satellites revolving at speed of
hamzaa
What are artificial satellites?
Scientists have sent many objects into space. Some of these objects
. These are called artificial satellites.”
: Most of the artificial satellites orbiting the earth are used for communication
How Newton’s law of gravitation helps in understanding the motion of satellites?
otion of Satellites: A satellite requires centripetal fo
The gravitational force of attraction between earth and satellite
understand the motion of satellites.
the orbital speed of a satellite depends?
ˢ = ˧ × ”
XX = ˧JI˰˩ˮIˮ˩JJIˬ III˥ˬ˥JIˮ˩JJ JJ ℎ˥˩˧ℎˮ X,
So, orbital speed of satellite depends on ˧ (˧JI˰˩ˮIˮ˩JJIˬ III˥ˬ˥JIˮ˩JJ JJ
J˦ ˥IJˮℎ - ˓ˬˮ˩ˮ˯ˤ˥).
communication satellites are stationed at
Satellites in Geostationary Orbits: Communication satellites are
stationed at geostationary orbits so that signal transmission
Communication satellites take 24 hours to complete their one
. As earth also completes its one rotation about its own axis in
be stationary. Hence they face no problem in signal transmission.
IMPORTANT SHORIMPORTANT SHORIMPORTANT SHORIMPORTANT SHORT QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORE
Describe navigation system. [L.B. 2014]
(Global Positioning System) is a satellite navigation system. It helps
of object anywhere on land, on sea and in air.
revolving at speed of 3.87 kms-1
around the earth.
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into space. Some of these objects
communication purposes.
How Newton’s law of gravitation helps in understanding the motion of satellites?
rce keeps it to
The gravitational force of attraction between earth and satellite
[L.B. 2016]
,
JJ ℎ˥˩˧ℎˮ X) and
to complete their one revolution
. As earth also completes its one rotation about its own axis in 24 hours so
be stationary. Hence they face no problem in signal transmission.
T QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORET QUESTIONS FROM BISE LAHORE
(Global Positioning System) is a satellite navigation system. It helps
around the earth.

P a g e | 20
02020202 What is the height and speed of geostationary satellite with respect to earth?[L.B. 2014]
Height of Geostationary Satellite: The height of geostationary satellite from centre of earth
is 42300 km and 35900 km from surface of the earth.
Speed of Geostationary Satellite: The speed of geostationary satellite with respect to earth
is zero.
03030303 How the equation ˧ = { {
changes when R is doubled? [L.B. 2015]
Change in gh: As by formula, X = { {
X ∝
#
{ {
∴ gh is inversely proportional to
{˞ - ℎ{$
At a height equal to one earth radius above earth surface, g becomes one fourth of its value
and so on.
04040404 What is the orbital speed of lower orbiting satellite? [L.B. 2016]
Orbital Speed: The orbital speed of lower orbiting satellite is 8000 m/s and can be calculated
by following formula ˢ = ˧ × ” .
05050505 Write the definition of satellite and give example. [L.B. 2017]
Satellite: “An object that revolves around a planet is called a satellite.”
Example: Moon revolves around earth. So moon is a natural satellite of earth.
06060606 What is meant by geostationary satellite? [L.B. 2017]
Geostationary Satellite: “The satellite which remains stationary with respect to earth is
called geostationary satellite.”
These satellites take 24 hours to complete their one revolution around the earth. The earth
also completes its one rotation about its axis in 24 hours. So these satellites appear to be
stationary with respect to earth.
07070707 Why we cannot feel gravitational force around us? [L.B. 2018]
Feeling Gravitational Force: Due to small value of G, the gravitational force of attraction
between objects around us is very small and we do not feel it.

P a g e | 21
nit 06
WORK AND ENERGYWORK AND ENERGYWORK AND ENERGYWORK AND ENERGY
6.2 Define work. What is its SI unit? [L.B. 2014,15,17]
Work: “Work is done when force acting on a body displaces it in the direction of the force.”
Unit: The SI unit of work is Joule (J).
Definition of Joule: “The amount of work done is one joule when a force of one newton
displaces a body through one metre in the direction of force.”
6.3 When does a force do work? Explain.
Work by Force: Work is said to be done when a force acts on a body and moves it in
direction of force. ͳ = ͨ × W
This work done depends on the force acting, displacement covered by body and the angle
between force and displacement.
6.4 Why do we need energy?
Need of Energy: As “Energy is the ability of a body to do work”
So, we need energy to do some useful work in daily life.
6.5 Define energy give two types of mechanical energy.
Energy: “A body possesses energy if it is capable to do work.”
Types: Two types of mechanical energy are 1) Kinetic Energy 2) Potential Energy.
6.6 Define K.E. and derive its relation. [L.B. 2014,15**]
Kinetic Energy: “The energy possessed by a body due to its motion is called its kinetic
energy.”
Formula: H. ˗. =
#
$
˭˰$
6.7 Define potential energy and derive its relation.
Potential Energy: “The energy possessed by a body due to its position is called its potential
energy.”
Formula: ˙JI˰˩ˮIˮ˩JJIˬ ˜Jˮ˥Jˮ˩Iˬ ˗J˥J˧˳ = ˭˧ℎ
U
H. ˗. = ˫˩J˥ˮ˩I ˥J˥J˧˳
˭ = ˭IJJ J˦ IJˤ˳
˰ = ˰˥ˬJI˩ˮ˳ J˦ IJˤ˳
˭ = ˭IJJ J˦ IJˤ˳
˧ = ˧JI˰˩ˮIˮ˩JJIˬ III˥ˬ˥JIˮ˩JJ
ℎ = ℎ˥˩˧ℎˮ

6.8 Why are fossil fuel called non
Fossil Fuels: Current supply of fossil fuels will soon be exhausted and f
millions of years for their format
sources of energy.
6.9 Which form of energy is
Preferred Energy Form: Electric energy
widely used because it is easy to convert in
6.10 How is energy converted from one form to another? Explain.
Energy Conversion: Energy can be converted from one form to another
doing work.
Explanation: For example, rub
warm. You have used your muscular energy in rubbing your hands. By the
process of rubbing mechanical energy can be converted into heat.
6.11 Name any five devices that convert electrical en
energy.
Devices: Following are the devices that convert electrical energy to mechanical energy.
1) Electric Fan 2) Electric Drill
6.12 Name a device that convert
Device: Electric Generator converts mechanical energy to electric energy.
6.13 What is meant by the efficiency of a system?
Efficiency of System: “Efficiency of a system is the
from the system as output to
˗˦˦˩I˩˥JI˳
˜˥JI˥JˮI˧˥ ˗˦˦˩I˩˥JI˳
Mechanical
Energy
hamzaa
Why are fossil fuel called non-renewable form of energy?
Current supply of fossil fuels will soon be exhausted and fossil fuels took
millions of years for their formation. That is why fossil fuels are called as non
Which form of energy is preferred and why?
Electric energy is preferred over other forms of energy and is
widely used because it is easy to convert in forms and easy to supply to any desired place.
How is energy converted from one form to another? Explain.
: Energy can be converted from one form to another by
rub your hands together quickly. You will feel them
process of rubbing mechanical energy can be converted into heat.
Name any five devices that convert electrical energy into mechanical
: Following are the devices that convert electrical energy to mechanical energy.
Electric Drill 3) Electric Motor 4) Washing Machine 5)
Name a device that converts mechanical energy to electrical energy.
converts mechanical energy to electric energy.
What is meant by the efficiency of a system?
Efficiency of a system is the ratio of required form of energy obtained
the total energy given to it as input.”
˗˦˦˩I˩˥JI˳ =
J˥J˯˩J˥ˤ ˦JJ˭ J˦ J˯ˮJ˯ˮ
ˮJˮIˬ ˩JJ˯ˮ ˥J˥J˧˳
˗˦˦˩I˩˥JI˳ =
J˥J˯˩J˥ˤ ˦JJ˭ J˦ J˯ˮJ˯ˮ
ˮJˮIˬ ˩JJ˯ˮ ˥J˥J˧˳
× 100
Electric
Generator
Electric Energy
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ossil fuels took
That is why fossil fuels are called as non-renewable
s of energy and is
forms and easy to supply to any desired place.
[L.B. 2014]
by
together quickly. You will feel them
ergy into mechanical
: Following are the devices that convert electrical energy to mechanical energy.
5) Sinner
mechanical energy to electrical energy. [L.B. 2016]
[L.B. 2014]
of required form of energy obtained
100
Electric Energy

P a g e | 23
6.14 How can you find the efficiency of a system?
Efficiency: Efficiency of a system can be calculated by dividing J˥J˯˩J˥ˤ ˦JJ˭ J˦ J˯ˮJ˯ˮ
on ˮJˮIˬ ˩JJ˯ˮ ˥J˥J˧˳. ˗˦˦˩I˩˥JI˳ =
6.15 What is meant by the term power? [L.B. 2014,15,16,17,18]
Power: “Power is defined as the rate of doing work.”
Formula: ˜ =
6.16 Define watt. [L.B. 2014,16]
Watt: “The power of a body is one watt if it does work at the rate of one joule per second.”
1 ˣ =
1 H
1 J
IMPORTANT SHORT QUESTIONS FROMIMPORTANT SHORT QUESTIONS FROMIMPORTANT SHORT QUESTIONS FROMIMPORTANT SHORT QUESTIONS FROM BISE LAHOREBISE LAHOREBISE LAHOREBISE LAHORE
01010101 Write Einstein’s equation and value of c. [L.B. 2014,15]
Einstein’s Equation: Einstein’s equation ͧ = ͽ͹ shows the relation between mass and
energy.
Here, ͹ = JJ˥˥ˤ J˦ ˬ˩˧ℎˮ = 3 × 10 ˭J #
02020202 What is difference between sound energy and mechanical energy? [L.B. 2014,15]
Sound Energy: “Sound energy is produced
by a vibrating surface.”
Mechanical Energy: “The energy possessed
by a body due to its motion or position is
called mechanical energy.”
03030303 Differentiate between chemical and mechanical energy. [L.B. 2015]
Chemical Energy: “The energy stored in
form of chemical bond in a substance is
called chemical energy.”
Mechanical Energy: “The energy possessed
by a body due to its motion or position is
called mechanical energy.”
04040404 Define mechanical energy and give example. [L.B. 2017]
Mechanical Energy: “The energy possessed by a body due to its motion or position is called
mechanical energy.”
Example: The energy possessed by running water or energy stored in stretched bow.
05050505 Write 2 major disadvantages of fossil fuels. [L.B. 2017]
Disadvantages of Fossil Fuels: 1) Fossil fuels causes air pollution. 2) Fossil Fuels are
nonrenewable sources of energy.

P a g e | 24
06060606 A body of mass 50 kg is raised to a height of 3 m. What is its potential energy? [L.B.
2018]
Potential Energy: ˭IJJ = 50 ˫˧, ℎ˥˩˧ℎˮ = 3 ˭, ˜. ˗. =
By definition, W. ͧ. = ͽXX
Substituting values, ˜. ˗. = {50{{10{{3{
˜. ˗. = 1500 H
07070707 What is meant by nuclear energy? [L.B. 2018]
Nuclear Energy: “Nuclear energy is the energy released in the form of nuclear radiations
during nuclear reactions such as fission and fusion reaction.”
Benefit: Heat energy released in nuclear reactors can be converted into electrical energy.
nit 07
PROPERTIES OF MATTERPROPERTIES OF MATTERPROPERTIES OF MATTERPROPERTIES OF MATTER
7.2 How is kinetic molecular model of matter helpful in differentiating various states of
matter? [L.B. 2014,16]
Kinetic Molecular Model: Kinetic molecular model of matter is helpful in differentiating
various states of matter as it describes all states as follows:
All states of matter are made up of particles called molecules.
The molecules remain in continuous motion.
Molecules attract each other.
7.3 Does there exist a fourth state of matter? What is that? [L.B. 2017]
Fourth State of Matter: Yes! Plasma is called fourth state of matter. At very high
temperature, the collisions between atoms and molecules tears off their electrons. Atoms
become positive ions. This ionic state of matter is called plasma.
7.4 What is meant by density? What is its SI unit? [L.B. 2017]
Density: “Density of a substance is defined as its mass per unit volume.”
Unit: The SI unit of density is kilogram per cubic metre (kgm-3
).
U

7.5 Can we use a hydrometer to measure the density of milk?
Hydrometer: Yes! A hydrometer can be used to measure the density of milk. The
hydrometer must be calibrated as
7.6 Define the term pressure.
Pressure: “The force acting normally
pressure.”
Formula:
7.7 Show that atmosphere exerts pressure.
Atmosphere Exerts Pressure:
water, over flame. Wait till water begins to boil and steam expels
the air out of the can. Now place the can
water, with closed cap. The steam in can condenses
water and changes into water leaving an empty space be
This lowers the pressure inside the can
outside will cause the can to collapse from all directions. This
shows that atmosphere exerts pressure.
7.8 It is easy to remove air from balloon but it is very difficult to remove air from
bottle. Why?
Air Removal: Balloon is filled with compressed gas or air. The pressure of air inside the
balloon is higher than outside. That is why air
pressure of air inside the bottle is same as outside.
bottle.
7.9 What is a barometer?
Barometer: “The instrument that
called barometer.”
Mercury barometer is a simple barometer that consist
filled with mercury and closed at one end
7.10 Why is water not suitable to be used in barometer?
Water in Barometer: The height of
times greater than that of mercury column i.e.
to greater density of water. Thus a glass tube more than
required to make a water barometer
barometer.
hamzaa
Can we use a hydrometer to measure the density of milk?
! A hydrometer can be used to measure the density of milk. The
hydrometer must be calibrated as lactometer to measure density of milk.
Define the term pressure. [L.B.
acting normally per unit area on the surface of a body is called
W΂X΃΃Y΂X =
ͨͿ΂͹X
V΂Xͷ
Show that atmosphere exerts pressure.
: Place a tin can, half filled with
water, over flame. Wait till water begins to boil and steam expels
the air out of the can. Now place the can, over chilled running
The steam in can condenses by running
water and changes into water leaving an empty space behind it.
This lowers the pressure inside the can and atmospheric pressure
outside will cause the can to collapse from all directions. This
shows that atmosphere exerts pressure.
It is easy to remove air from balloon but it is very difficult to remove air from
Balloon is filled with compressed gas or air. The pressure of air inside the
balloon is higher than outside. That is why air rushes out from balloon easily
pressure of air inside the bottle is same as outside. Hence it is difficult to remove air from
that measures the atmospheric pressure is
a simple barometer that consist 1 m long glass tube
and closed at one end.
Why is water not suitable to be used in barometer? [L.B. 2014
The height of water column at sea level will be 13.6
times greater than that of mercury column i.e. 0.76 m x 13.6 = 10.34 m due
. Thus a glass tube more than 10 m long is
required to make a water barometer. That is why water is not suitable to be used in
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! A hydrometer can be used to measure the density of milk. The
[L.B. 2015,16**,18]
on the surface of a body is called
It is easy to remove air from balloon but it is very difficult to remove air from a glass
Balloon is filled with compressed gas or air. The pressure of air inside the
rushes out from balloon easily while the
Hence it is difficult to remove air from
[L.B. 2018]
1 m long glass tube
2014]
due
be used in

7.11 What makes a sucker pressed on a smooth wall sticks to it?
Sucker: The air between sucker and wall expels out on pressing it hence
outside atmospheric pressure
makes the sucker pressed on the wall.
7.12 Why does atmospheric pressure vary with height?
Atmospheric Pressure Variation
of air changes with height hence
7.13 What does it mean when the atmospheric pressure at a place fall suddenly?
Atmospheric Pressure Fall Suddenly
and showery condition in the nearby region.
7.14 What changes are expected in weather if the barometer reading shows a sudden
increase?
Changes in Weather: A sudden increase in reading shows
with a decline later on predicting an
7.15 State Pascal’s law.
Pascal’s Law: “Pressure applied
container, is transmitted without loss
Applications: Pascal’s law finds its numerous applications in
automobiles, hydraulic brake system, hydraulic jack and hydraulic
press etc.
7.17 What is meant by elasticity?
Elasticity: “The property of a body to
ceases to act is called elasticity.
7.18 State Archimedes principle.
Archimedes Principle: “When an object is totally or partially immersed in a liquid, an
upthrust acts on it equal to the
7.19 What is upthrust? Explain the principle of floatation.
Upthrust: “Upthrust on a body immersed in liquid
displaced.”
Principle of Floatation: “A floating object displaces a fluid having weight equal to the weight
of the object.”
hamzaa
What makes a sucker pressed on a smooth wall sticks to it?
The air between sucker and wall expels out on pressing it hence
atmospheric pressure becomes higher than inside pressure and
makes the sucker pressed on the wall.
Why does atmospheric pressure vary with height?
Atmospheric Pressure Variation: Atmospheric pressure depends on density
of air changes with height hence atmospheric pressure varies with height.
What does it mean when the atmospheric pressure at a place fall suddenly?
Atmospheric Pressure Fall Suddenly: Rapid fall in atmospheric pressure indicates a
condition in the nearby region.
What changes are expected in weather if the barometer reading shows a sudden
A sudden increase in reading shows increase in atmospheric pressure
with a decline later on predicting an intense weather condition.
[L.B. 2015**,17]
applied at any point of a liquid enclosed in a
without loss to all other parts of the liquid.”
law finds its numerous applications in
automobiles, hydraulic brake system, hydraulic jack and hydraulic
What is meant by elasticity?
The property of a body to restore its original size and shape as deforming force
ceases to act is called elasticity.”
State Archimedes principle.
When an object is totally or partially immersed in a liquid, an
to the weight of the liquid it displaces.
thrust? Explain the principle of floatation.
Upthrust on a body immersed in liquid is equal to the weight of the liquid
A floating object displaces a fluid having weight equal to the weight
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density of air. Density
What does it mean when the atmospheric pressure at a place fall suddenly?
Rapid fall in atmospheric pressure indicates a windy
What changes are expected in weather if the barometer reading shows a sudden
in atmospheric pressure
[L.B. 2016,17**]
as deforming force
[L.B. 2016]
When an object is totally or partially immersed in a liquid, an
ual to the weight of the liquid
A floating object displaces a fluid having weight equal to the weight

7.20 Explain how a submarine floats on the water surface
and dives down in water?
Submarine Floats: Submarine floats over water when
weight of water equal to its volume is greater than its
weight.
Submarine Dives: Submarine dives into water when its
tanks are filled with seawater and its weight increases than upthrust.
7.21 Why does a piece of stone sink in water but a ship with a huge weight floats?
Piece of Stone: Piece of stone sinks in water because the weight of displaced water is less
than its own weight.
Ship Floats: Ship floats over water because the weight of displaced
own weight.
7.22 What is Hook’s law? What is meant by elastic limit?
Hook’s Law: “The strain produced in a body by the stress applied to it is directly
proportional to the stress within the elastic limit of the body.”
7.23 Take a rubber band. Construct a balance of your
accuracy by weighing various objects.
00001111 The mass of 200 cm3
of stone is 500 g. Find its density.
Density: ˭IJJ =
By definition,
Substituting values,
02020202 Define stress.
Stress: “The force acting on unit area
Unit: In SI the unit of stress is newton per square metre (
hamzaa
Explain how a submarine floats on the water surface
Submarine floats over water when
weight of water equal to its volume is greater than its
: Submarine dives into water when its
tanks are filled with seawater and its weight increases than upthrust.
stone sink in water but a ship with a huge weight floats?
: Piece of stone sinks in water because the weight of displaced water is less
: Ship floats over water because the weight of displaced water is greater than its
What is Hook’s law? What is meant by elastic limit?
The strain produced in a body by the stress applied to it is directly
within the elastic limit of the body.”
΃Y΂X΃΃
΃Y΂ͷX;
= ͹Ϳ;΃Yͷ;Y
Take a rubber band. Construct a balance of your own using rubber band. Check its
accuracy by weighing various objects.
of stone is 500 g. Find its density.
= 500 ˧, ˰Jˬ˯˭˥ = 200 I˭%
, ˖˥JJ˩ˮ˳
ͦX;΃XYY =
ͽͷ΃΃
ͲͿͼYͽX
˖˥JJ˩ˮ˳ =
'""
$""
˖˥JJ˩ˮ˳ = 2.5 ˧ I˭ %
unit area at the surface of a body is called stress.”
: In SI the unit of stress is newton per square metre ( W ͽ ).
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stone sink in water but a ship with a huge weight floats? [L.B. 2014,15]
: Piece of stone sinks in water because the weight of displaced water is less
water is greater than its
[L.B. 2017]
The strain produced in a body by the stress applied to it is directly
own using rubber band. Check its
[L.B. 2014,18]
˖˥JJ˩ˮ˳ =
[L.B. 2016]
at the surface of a body is called stress.”

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nit 08
THERMAL PROPERTIES OF MATTERTHERMAL PROPERTIES OF MATTERTHERMAL PROPERTIES OF MATTERTHERMAL PROPERTIES OF MATTER
8.2 Why does heat flows from hot body to cold body?
Heat Flow: When two bodies of different temperature come into contact with each other,
the temperature of the hot body falls and it loses energy. This energy enters the cold body
due to which its temperature rises. The transfer of energy continues till both bodies have
the same temperature.
8.3 Define the terms heat and temperature. [L.B. 2014**,16**]
Heat: “Heat is the energy that is transferred from one body to the other in thermal contact
with each other as a result of the difference of temperature between them.”
Unit: Unit of Heat energy is joule (J).
Temperature: “Temperature of the body is the degree of hotness or coldness of the body.”
Unit: SI unit of temperature is Kelvin (K).
8.4 What is meant by internal energy of a body? [L.B. 2014]
Internal Energy: “The sum of kinetic energy and potential energy associated with the atoms,
molecules and particles of a body is called its internal energy.”
HJˮ˥JJIˬ ˗J˥J˧˳ = ͭ. ͧ. -W. ͧ.
8.5 How does heating affect the motion of molecules of a gas? [L.B. 2015]
Effect of Heat: Gas molecules move randomly and when heat energy is given to these
molecules their kinetic energy increases due to which their velocity is increased.
8.6 What is thermometer? Why mercury is preferred as a thermometric substance?
Thermometer: “A device which is used to measure the temperature of a body is called
thermometer.”
Mercury as Thermometric Material: Mercury is preferred as thermometric material
because it has all the thermometric properties like low freezing point i.e. -39o
C, high boiling
point i.e. 357o
C and small specific heat capacity.
U

P a g e | 29
8.7 Explain the volumetric thermal expansion.
Volumetric Thermal Expansion: “The volume of a solid changes with the change in
temperature and is called as volumetric thermal expansion.”
˕ℎIJ˧˥ ˩J ˰Jˬ˯˭˥ = ˢ − ˢ = ˢ ∆ˠ
8.8 Define specific heat. How would you find the specific heat of solid?[L.B. 2014,15,17,18]
Specific Heat: “Specific heat of the substance is the amount of heat required to raise the
temperature of 1 kg mass of that substance through 1 K.”
Formula: ˟J˥I˩˦˩I H˥Iˮ = ͹ =
∆W
ͽ∆Ͱ
8.9 Define and explain latent heat of fusion. [L.B. 2016]
Latent Heat of Fusion: “Heat energy required to change unit mass of a substance from solid
to liquid state at its melting point without any change in its temperature is called its latent
heat of fusion.”
Formula: HIˮ˥Jˮ H˥Iˮ J˦ ˘˯J˩JJ = ͪX =
∆WX
ͽ
8.10 Define and explain latent heat of vaporizations.
Latent Heat of Vaporization: “Heat energy required to change unit mass of a liquid
completely into gas at its boiling point without any change in its temperature is called its
latent heat of vaporization.”
Formula: HIˮ˥Jˮ H˥Iˮ J˦ ˢIJJJ˩˴Iˮ˩JJ = ͪY =
∆WY
ͽ
8.11 What is meant by evaporation? On what factors the evaporation of a liquid
depends? Explain how cooling is produced by evaporation? [L.B. 2015]
Evaporation: “Evaporation is the changing of a liquid into vapours from the surface of liquid
without heating it.”
Factors: Evaporation of a liquid depends on temperature, surface area, wind and nature of
liquid.
Evaporation Causes Cooling: During evaporation, fast moving molecules escape from the
surface of liquid leaving lower K.E. molecules behind. This lowers the average kinetic energy
of liquid molecules and temperature of liquid. Hence evaporation causes cooling.

P a g e | 30
01010101 What will be the temperature on Kelvin scale when it is 20 C° on Celsius scale? [L.B. 2014]
Temperature: ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { = 20 C°, ˠ˥˭J˥JIˮ˯J˥ = ˠ{H{ =
By Formula, ˠ˥˭J˥JIˮ˯J˥ = Ͱ{ͭ{ = Ͱ{VͿ{ -
Substituting values, ˠ˥˭J˥JIˮ˯J˥ = ˠ{H{ = 20 - 273 H
ˠ˥˭J˥JIˮ˯J˥ = ˠ{H{ = 2%3 H
02020202 Define coefficient of linear thermal expansion. [L.B. 2014]
Coefficient of Linear Thermal Expansion: “Coefficient of linear thermal expansion of a
substance is defined as the fractional increase in its length per Kelvin rise in temperature.”
C‘‡ˆ ‹…‹‡– ‘ˆ l‹‡a” –Š‡”al ‡xpas‹‘ = =
∆ͮ
ͮͿ∆Ͱ
03030303 Convert 100 F° into temperature on Celsius scale. [L.B. 2014,18]
Temperature: ˠ˥˭J˥JIˮ˯J˥ = ˠ{˘{ = 100 F°, ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { =
By Formula, ˠ˥˭J˥JIˮ˯J˥ = Ͱ{VͿ{ =
Ͱ{ͨͿ{
.
Substituting values, ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { =
#"" %$
#.
=
#.
ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { = 37.8 ˕
04040404 What is meant by thermal equilibrium? [L.B. 2015]
Thermal Equilibrium: “The property of a system when all parts of the system have the same
temperature along with its surrounding.”
05050505 Write 2 uses of bimetallic strip. [L.B. 2015]
Uses: Following are uses of bimetallic strip; 1) Bimetallic strips are used in thermostats. 2)
Bimetal thermometer is used to measure temperature in furnaces and oven.
06060606 What is meant by upper and lower fixed points of thermometer? [L.B. 2015]
Upper Fixed Point: “The upper fixed point is the mark that shows the position of mercury in
the thermometer when it is placed in steam from boiling water at standard pressure.”
Lower Fixed Point: “The lower fixed point is the mark that shows the position of mercury in
the thermometer when it is placed in ice”

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07070707 Convert 300 K into temperature on Celsius scale. [L.B. 2014]
Temperature: ˠ˥˭J˥JIˮ˯J˥ = ˠ{H{ = 300 K, ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { =
By Formula, ˠ˥˭J˥JIˮ˯J˥ = Ͱ{VͿ{ = Ͱ{ͭ{ −
Substituting values, ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { = 300 − 273 ˕
ˠ˥˭J˥JIˮ˯J˥ = ˠ{˕ { = 27 ˕
08080808 Write the names of types of latent heat. [L.B. 2015]
Types of Latent Heat: Two types of latent heat are 1) Latent Heat of Fusion and 2) Latent
Heat of vaporization.
09090909 Write two applications of thermal expansion. [L.B. 2016]
Applications: 1) Thermal expansion is used in thermometer for temperature
measurements. 2) Fixation of iron rims on wooden wheels. 3) Use of bimetallic strip
10101010 Define thermal expansion. [L.B. 2016]
Thermal Expansion: “Most of the substances expand on heating, this phenomenon is called
thermal expansion.”
Types: Its 2 types are linear thermal expansion and volumetric thermal expansion.
11111111 Which scales are used to measure temperature? [L.B. 2017]
Scales: Three scales are used to measure temperature. 1) Celsius Scale or Centigrade Scale
2) Fahrenheit Scale 3) Kelvin Scale.
12121212 What is meant by melting point and freezing point? [L.B. 2017]
Melting Point: “The temperature at which a solid starts melting is called its melting point.”
Freezing Point: “The temperature at which a substance changes from liquid to solid is called
its freezing point.”
13131313 Gaps are left in railway tracks. Why? [L.B. 2017]
Railway Track Gaps: Gaps are left in railway tracks to compensate thermal expansion during
hot season.

nit 09
9.2 Why are metals good conductors of heat?
Metals: Metals have free electrons
motion and can transfer heat
part to cold part. So metals are conductors due to free electrons.
9.3 Explain why:
a. A metal feels colder to touch than wood kept in a cold place?
Metal Feels Colder: Metal is good conductor
heat energy from your hand on touching
b. Land breeze blows from land to sea?
Land Breeze: At night, the land cools faster than the sea.
Therefore, air above the sea is warmer, ris
air from the land begins to move towards the sea. It is called
land breeze.
c. Double walled glass vessel is used in thermos flask?
Double Walled Glass Vessel: Double walled glass vessel is used
Vacuum between Double walled glass vessel
Outer glass vessel is silvered from inner side and the other from outside which
reduces heat transfer by radiation.
d. Deserts soon get hot during the day and soon get cold after sunset?
Deserts: Deserts soon get hot during the day and soon get cold after sunset
specific heat capacity of sand i.e.
9.4 Why conduction of heat does not take place in gases?
Conduction in Gases: Conduction can take place
or due to free electrons. Gases do not have closely packed molecules or free electrons. That
is why gases are not good conductors of heat.
U
hamzaa
TRANSFER OF HEATTRANSFER OF HEATTRANSFER OF HEATTRANSFER OF HEAT
Why are metals good conductors of heat?
free electrons which remain in continuous
motion and can transfer heat energy at a very fast rate from hot
So metals are conductors due to free electrons.
A metal feels colder to touch than wood kept in a cold place?
good conductor while wood is insulator. Metal
heat energy from your hand on touching, due to which it feels colder.
Land breeze blows from land to sea?
t night, the land cools faster than the sea.
Therefore, air above the sea is warmer, rises up and the cold
air from the land begins to move towards the sea. It is called
Double walled glass vessel is used in thermos flask?
: Double walled glass vessel is used to reduce heat transfer
Double walled glass vessels reduces conduction of heat.
reduces heat transfer by radiation.
Deserts soon get hot during the day and soon get cold after sunset?
s soon get hot during the day and soon get cold after sunset
capacity of sand i.e. 835.0 J kg-1
K-1
.
Why conduction of heat does not take place in gases?
Conduction can take place due to vibrations of molecules packed close
is why gases are not good conductors of heat.
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while wood is insulator. Metal transfers the
reduce heat transfer as;
reduces conduction of heat.
Deserts soon get hot during the day and soon get cold after sunset?
s soon get hot during the day and soon get cold after sunset due to less
due to vibrations of molecules packed close

9.5 What measures do you suggest to conserve energy in houses?
Conserve Energy in Houses: Following measures may be taken to conserve energy;
Hot water tanks are insulated by plastic or foam lagging.
Wall cavities are filled with plastic foam or wool.
9.6 Why does transfer of heat in fluids
Transfer of Heat in Fluids: Molecules of fluids are far apart due to weak intermolecular
forces. On heating these molecules move from hotter place to colder place and hence
transfer heat by convection.
9.7 What is meant by conve
Convection Current: “On heating,
which is called convection current.”
Example: Rise of smoke from chimneys
9.9 How does the heat reach us from the sun?
Heat from Sun: The heat energy reaches us neither by conduction nor by convection,
because the space between Sun and
that heat reaches us from the sun.
9.11 What is greenhouse effect?
Greenhouse Effect: “Layer of
vapours traps infrared radiations emitting out from earth
surface and does not allow them to escape
like greenhouse. This phenomenon is called greenhouse
effect.”
Greenhouse effect causes rise
called global warming.
9.12 Explain the impact of greenhouse effect in global warming?
Impact: During the recent years, the percentage of
This has caused an increase in average
This has serious implications for the global climate.
hamzaa
What measures do you suggest to conserve energy in houses?
Following measures may be taken to conserve energy;
Hot water tanks are insulated by plastic or foam lagging.
Wall cavities are filled with plastic foam or wool.
Why does transfer of heat in fluids take place by convection?
Molecules of fluids are far apart due to weak intermolecular
hese molecules move from hotter place to colder place and hence
is meant by convection current?
On heating, molecules of fluid start flow from hot part to cold
which is called convection current.”
Rise of smoke from chimneys is an example of convection current.
How does the heat reach us from the sun?
The heat energy reaches us neither by conduction nor by convection,
un and Earth’s atmosphere is empty. It is through
that heat reaches us from the sun.
house effect?
“Layer of carbon dioxide and water
infrared radiations emitting out from earth
surface and does not allow them to escape, hence behaves
like greenhouse. This phenomenon is called greenhouse
rise in average earth temperature
Explain the impact of greenhouse effect in global warming?
During the recent years, the percentage of CO2 has been increased
in average temperature of earth which is called global warming.
This has serious implications for the global climate.
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[L.B. 2016**]
Following measures may be taken to conserve energy;
Molecules of fluids are far apart due to weak intermolecular
hese molecules move from hotter place to colder place and hence
[L.B. 2018]
from hot part to cold part
is an example of convection current.
[L.B. 2016]
The heat energy reaches us neither by conduction nor by convection,
It is through radiation
[L.B. 2015,17**]
increased considerably.
which is called global warming.

IMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONS
00001111 Write the names of modes of transfer of heat.
Modes of Heat Transfer: 1) Conduc
transfer.
00002222 Why dark colored clothes are prohibited to wear in summer?
Dark Colored Clothes: Dark colored clothes being
cause us to feel hot. That is why dark colored clothes
03030303 Differentiate between land breeze and sea breeze.
Land Breeze: “Land breeze blows
to sea during night.”
04040404 Define thermal conductivity.
Thermal Conductivity: “The rate of flow of heat across the opposite faces of a
of a substance maintained at a temperature difference of
conductivity of that substance.”
05050505 Describe the effect of length on thermal conductivity.
Effect of Length: Thermal conductivity is a material property and is independent of change
in length, but rate of heat flow
.
hamzaa
IMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONSIMPORTANT SHORT QUESTIONS FROM BISE LAHOREFROM BISE LAHOREFROM BISE LAHOREFROM BISE LAHORE
Write the names of modes of transfer of heat.
Conduction 2) Convection 3) Radiation, are three modes of heat
clothes are prohibited to wear in summer?
Dark colored clothes being good absorber of heat radiations
That is why dark colored clothes are prohibited to wear in sum
Differentiate between land breeze and sea breeze.
blows from land Sea Breeze: “Sea breeze blows
land during day time.”
Define thermal conductivity.
The rate of flow of heat across the opposite faces of a
of a substance maintained at a temperature difference of one kelvin is called the thermal
conductivity of that substance.”
ͻ =
W
Y
×
V{Ͱ − Ͱ {
Describe the effect of length on thermal conductivity.
Thermal conductivity is a material property and is independent of change
rate of heat flow through a sample changes inversely with length
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FROM BISE LAHOREFROM BISE LAHOREFROM BISE LAHOREFROM BISE LAHORE
[L.B. 2014]
are three modes of heat
[L.B. 2014,17]
radiations can
are prohibited to wear in summer.
[L.B. 2014]
blows from sea to
[L.B. 2014]
The rate of flow of heat across the opposite faces of a metre cube
is called the thermal
[L.B. 2015**]
Thermal conductivity is a material property and is independent of change
with length

P a g e | 35
06060606 On which factors radiations depend? [L.B. 2015]
Radiations Dependence: The rate of emission of radiation depends on 1) Colour & Texture
of surface 2) Surface Temperature 3) Surface Area
07070707 Define convection. [L.B. 2016**,17]
Convection: “Transfer of heat by actual movement of molecules from hot place to a cold
place is known as convection.”
08080808 Describe the effect of cross sectional area on thermal conductivity. [L.B. 2017]
Effect of Area: Thermal conductivity is a material property and is independent of change in
cross sectional area, but rate of heat flow through a sample changes directly with cross
sectional area.
09090909 What causes a glider to remain in air? [L.B. 2017]
Glider: “Gliders ride over thermals (upward moving hot air currents due to convection). The
upward movement of air currents in thermals helps them to stay in air for a long period.
10101010 Write two names of expert thermal climbers. [L.B. 2018]
Expert Thermal Climbers: Eagles, hawks and vultures are expert thermal climbers.

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