Electric charges Current Potentialand its difference Circuits Heating effects Magnetic effects Magnetic Field Lines in straight and coiled conductors Electromagnets Electromagnetic Induction Motors and Generators

1. Topics covered
Electric Charge
Electric Current
Electric Potential
Electrical Resistance
Ohm’s Law
Series and parallel connection of resistors
Electric Power
Electric Energy & its commercial Unit
Heating Effects of Electric Current

2. STATIC ELECTRICITY

3. TYPES OF ELECTRIC CHARGES
There are two types of Electric Charges:
Positive Charges
Negative Charges
By Convention,
The charge acquired by a glass rod is called Positive Charge
The charge acquired by an ebonite rod is called Negative Charge
Opposite charges (or Unlike charges) attract each other.
Similar charges (or Like charges) repel each other.

4. SI UNITS OF CHARGE
SI Unit of Charge is Coulomb, denoted by C
One Coulomb is that quality of electric charge which exerts a force of
9 * 109 N on an equal charge placed at a distance of 1 metre from it.
Charge possessed by an electron is 1.6 * 10-19 Coulombs

5. Conductors & Insulators
Substances through which electricity can flow are called Conductors.
Ex: Silver, Copper and Aluminium, etc
Those Substances through which electric charges cannot flow, are called
Insulators.
Ex: Glass, Ebonite, Rubber, most plastics, Paper, Dry wood, Cotton,
Mica, Bakelite, Porcelain, and Dry Air

6. What makes Substances Conduct
Electricity?
The presence of Free Electrons in a substance makes it a conductor.
The electrons present in insulators are strongly held by the nuclei of their
atoms.
So no free electrons in an insulator which can move from one atom to
another, an insulator does not allow electric charges to flow through it.
Static Electricity ?

7. Electric Potential
What happens when a positive charge is placed in the electric field due to
another charge?

8. Electric Potential
Electric potential at a point in an electric field is defined as the work
done in moving a unit positive charge from infinity to that point.

9. Potential Difference
The difference between two points in an electric circuit is defined as the
amount of work done in moving a unit charge from one point to the other
point.
Potential difference = Work done / Quantity of Charge moved

10. Heating Effects of Electric Current
When an electric current is passed through a high
resistance wire, like nichrome wire, the resistance wire
becomes very hot and produces heat.
This is called as the Heating effects of Electric current

12. MAGNETIC EFFECTS OF
ELECTRIC CURRENT

13. Learning Objectives
Magnetic Field and Magnetic Field Lines
Magnetic Field of Earth
Electromagnetism
Magnetic field patterns produced by current carrying
Conductors of various shapes
Electromagnet
Difference between Bar Magnet & an Electromagnet
Magnetism in Human Body

14. Learning Objectives
Force on a current carrying conductor placed in a
magnetic field
Kicking Wire Experiment
Fleming’s Left Hand Rule
Principle and working of Electric Motor
Electromagnetic Induction
Fleming’s Right-Hand Rule
Electric Generator- AC & DC Generators
Domestic Electrical Wiring

15. Magnetic Effect of Electric Current
“An electric current flowing in a wire produces a magnetic
field around it”
Electric Current produces Magnetism

16. Magnet & Magnetic Field
A magnet is an object which attracts pieces of
iron, steel, nickel and cobalt
The space around a magnet in which magnetic
force is exerted, is called a magnetic field

18. Magnetic Field Lines
The lines drawn in a magnetic field along which a north
magnetic pole would move
The magnetic field lines are also known as magnetic lines
of force
The magnetic field lines always begin from the N-pole of
magnet and end on the S-pole of the magnet

20. DEMONSTRATION ON MAGNETIC
FIELD LINES

21. Properties of Magnetic Field Lines
The magnetic field lines originate from the North pole of a
magnet and end at its south pole
The magnetic field lines come closer to one another near
the poles of a magnet but they are widely separated at
other places
The magnetic field lines do not intersect one another

23. Magnetic Field of Earth
A freely suspended magnet always points in the north-south direction even
in the absence of any other magnetic field.
This suggests that the earth itself behaves as a magnet which causes a
freely suspended magnet to point always in a particular direction
The shape of the earths magnetic field resembles that of an bar magnet

25. The axis of Earth’s Magnetic Field is inclined at an angle of
about 150 with the geometrical axis

26. The Earth’s magnetic Field is due to the Magnetic Effect of
Current, which is flowing in the liquid core at the centre of
the earth
Thus, Earth is a huge electromagnet
Why Earth’s Magnetic Field

27. Questions
1. State any two properties of Magnetic Field lines.
2. (True/False) The axis of earth’s imaginary magnet and the geographical axis
coincide with each other
3. Where do the manufacturers use a magnetic strip in the refrigrator? Why is
this magnetic strip used?
4. Why does a compass needle get deflected when brought near a bar magnet?

29. ELECTROMAGNETISM
MAGNETIC EFFECTS OF CURRENT

30. ELECTROMAGNETISM
The magnetic effect of current was discovered by oersted in 1820
Oersted found that a wire carrying a current was able to deflect a compass
needle
Compass needle is a tiny magnet which can be deflected only by a magnetic
field
Since, a current carrying wire was able to deflect a compass needle, it was
concluded that a current flowing in a wire always gives rise to a magnetic
field around it

31. ELECTROMAGNETISM
The importance of magnetic effect of electric current lies in the fact that it
gives rise to mechanical forces
The Electric Motor,
Electric Generator,
Telephone and Radio
All the above devices utilise the magnetic effects of electric current
The magnetic effects of electric current is also called electromagnetism which
means electricity produces magnetism

33. MAGNETIC FIELD PATTERNS
By current-carrying conductors of various shapes

35. Magnetic Field due to straight current
carrying wire

36. Magnetic Field due to straight current
carrying wire
The magnetic field lines around a straight conductor
carrying current are concentric circles whose centres lie
on the wire
The magnitude of magnetic field produced by a straight current carrying
wire at a given point is:
Directly proportional to the current passing in the wire, and
Inversely proportional to the distance of that point from the wire

37. Important observations
Greater the current in the wire, stronger will be the
magnetic field produced
Greater the distance of a point from the wire current
carrying wire, weaker will be the magnetic field
produced at that point
As we move away from a current-carrying straight wire,
the concentric circles around it representing magnetic
field lines, becomes larger and larger indicating the
decreasing strength of the magnetic field

38. Right-Hand Thumb Rule
(Maxwell’s Right-Hand Thumb Rule)

39. Direction of Magnetic Field for a straight current
carrying conductor
Imagine that you are holding a current carrying conductor in your right hand so that
your thumb points in the direction of current, then the direction in which your
fingers encircle the wire will give the direction of magnetic field lines around the
wire
Maxwell’s Right-Hand thumb rule is also known as Maxwell’s corkscrew rule

40. Magnetic Field Pattern due to Circular Loop
(Circular Wire)

41. Important Observations
It has been found that the magnetic effect of current increases if instead of
using a straight wire, the wire is converted into a circular loop
Magnetic field lines are circular near the current carrying loop, as we move
away the concentric circles representing magnetic field lines become bigger
and bigger
At the centre of the circular loop, the magnetic field lines are straight
At the centre of the circular loop, all the magnetic field lines are in the same
direction and aid each other, due to which the strength of magnetic field
increases

42. Important Observations
The magnitude of magnetic field produced by a current-carrying circular loop
at its centre is:
Directly proportional to the current passing through the circular loop and
inversely proportional to the radius of circular loop

43. How to increase the strength of the magnetic field in
a circular coil ?
The strength of the magnetic field can be increased by taking a
circular coil consisting of a number of turns of insulated copper
wire closely wound together.
If there is a circular coil having n turns, the magnetic field
produced by this current-carrying circular wire will be n times as
large as that produced by a circular loop of a single turn of wire.

44. Important Observations
The strength of a magnetic field produced by a circular coil carrying current is directly
proportional to both, number of turns (n) and current (I); but inversely proportional to
its radius (r).
The Strength of the magnetic field produced by a current-carrying circular coil can be
increased:
by increasing the number of turns of wire in the coil,
by increasing the current flowing through the coil, and
by decreasing the radius of the coil

45. Clock Face Rule
A Current-carrying circular wire behave like a thin disc magnet
whose one face is a north pole and the other face is a south pole.

46. According to Clock face Rule
If the current in the circular wire is in the clockwise
direction, then that face of the circualar wire will be
South pole
If the current around the face of circular wire flows in the
anticlockwise direction, then that face of the circular
wire will be North pole

47. Magnetic Field due to a Solenoid
A solenoid is a coil containing a large number
of close turns of insulated copper wire

48. Magnetic Field due to a Solenoid
The magnetic Field produced by a current carrying
Solenoid is similar to the magnetic field produced by a bar
magnet

49. Important Observations
The lines of the magnetic field pass through the Solenoid and return to the
other end
The magnetic field inside the Solenoid are in the form of parallel straight
lines
This indicates that the strength of the magnetic field is same at all points inside
the solenoid
If the strength of the magnetic field is uniform just same in a region, it is said to
be uniform magnetic field
Thus, magnetic field is uniform inside a currnet carrying Solenoid

50. Important Observations
The strength of the magnetic field produced by a current
carrying Solenoid depends on:
The number of turns in the Solenoid. Larger the number of turns in the
Solenoid, greater will be the magnetism produced
The strength of current in the Solenoid. Larger the current passed through
the Solenoid, stronger will be the magnetic field produced
The nature of core material used in the Solenoid. The use of Soft Iron rod as
core in a Solenoid produces the strongest magnetism

51. Electromagnet
An electric current can be used for making temporary
magnets known as electromagnets.
An electromagnet works on the magnetic effect of current.

52. Electromagnet
An Electromagnet is a magnet consisting of a long coil of insulated
copper wire wrapped around a soft iron core that is magnetised
only when electric current is passed through the coil
The core of the Electromagnet should be Soft iron because soft
iron loses all of its magnetism when current in the coil is switched
off

53. Bar magnet vs Electromagnet
Bar magnet is a permanent magnet
A permanent magnet produces a
comparatively weak force of
attraction
The strength of a permanent magnet
cannot be changed
The polarity of a permanent magnet
is fixed and cannot be changed
An electromagnet is a temporary magnet.
Its magnetism is only for the duration of
current passing through it
An Electromagnet can produce very strong
magnetic force
The strength of the electromagnet can be
changed by altering the current
The polarity of an electromagnet can be
changed by changing the direction of
current in its coil

54. Permanent magnets are usually made of alloys such as:
Carbon steel, Chromium Steel, Cobalt Steel, Tungsten Steel
and Alnico
Alnico is an alloy of aluminium, nickel, cobalt and iron
Permanent Magnets

55. Magnetic Fields in Human Body
Extremely weak electric currents are produced in the human body
by the movement of charged particles called ions. These are called
ionic currents.
These create temporary magnetism in the human body. The
magnetism produced in the human body is very very weak
compared to the earth’s magnetic field.

56. Magnetism in Human Body
The two main organs of the human body where the
magnetic field produced is quite significant are the heart
and the brain
This magnetism forms the basis of a technique called
Magnetic Resonance Imaging (MRI) which is used to
obtain internal parts of our body.

57. Force on current carrying conductor
placed in a Magnetic Field

58. Observations from Oersted’s
Experiment
A current-carrying wire exerts a force on a compass needle and deflects it
from its usual north-south position
A current-carrying wire exerts a mechanical force on a magnet, and if the
magnet is free to move, this force can produce a motion in the magnet
A magnet exerts a mechanical force on a current-carrying wire, and if the
wire is free to move, this force can produce a motion in the wire
This can be obtained by applying Newton’s Third Law

59. Why Force being acted upon a Current
carrying wire in a magnetic field ?

60. Faraday’s Observation in 1821
When a current-carrying conductor is placed in a magnetic
field, a mechanical force is exerted on the conductor which
can make the conductor move
This is the Working Principle of a Motor

63. Important Observations
● When a current-carrying conductor is placed in a magnetic field, a
mechanical force is exerted on the conductor which makes it move
● The direction of force acting on a current-carrying conductor placed in a
magnetic field is:
i. Perpendicular to the direction of current
ii. Perpendicular to the direction of magnetic field
Important point:
● Maximum force is exerted on a current-carrying wire only
when it is perpendicular to the direction of magnetic field.
● No force acts on the current-carrying wire when it is parallel to
the magnetic field

65. Important Observations
The direction of force on a current-carrying conductor placed in a magnetic
field can be reversed by reversing the direction of current flowing in the
conductor
If the direction of current in a conductor and the
direction of magnetic field(in which it is placed), are
known, then the direction of force acting on the
current-carrying conductor can be found out by using
Fleming’s left-hand rule.

66. Fleming’s Left Hand Rule

67. Statement
Hold the forefinger, the centre finger and the thumb of your
left hand at right angles to one another.
Adjust your hand in such a way that the forefinger points in
the direction of magnetic field and the centre finger points
in the direction of current in the conductor, then the
direction in which the thumb points gives the direction of
motion of the conductor

68. ELECTRIC CURRENT
ALTERNATING CURRENT (AC)DIRECT CURRENT (DC)

69. Sources of DC & AC
DC
Batteries
Thermocouples
Solar Cells
Dynamo
Direct current is also known as
Galvanic Current
All the electronic devices work
on Direct Current only
AC
AC Generators
All Electrical devices work on
AC Supply
We receive AC supply

70. Alternating Current can be transmitted
over long distances without much loss
of electrical energy
ADVANTAGES OF AC OVER DC

71. The Electric Motor
Principle, Construction, Working & Applications

72. THE ELECTRIC MOTOR
A Motor is a device which converts Electrical
energy into Mechanical energy

73. Principle of a DC Motor

74. Principle of a Motor
An electric motor utilises the magnetic effect of current.
A motor works on the principle that when a rectangular coil
is placed in a magnetic field and current is passed through
it, a force acts on the coil which rotates it continuously.
When the coil rotates, the shaft attached to it also rotates.
In this way the electrical energy supplied to the motor is
converted into the mechanical energy of rotation

75. Construction of a DC Motor

77. Construction of a Motor
1. An electric motor consists of a rectangular coil ABCD of insulated copper wire, which is mounted between
the curved poles of a horseshoe type permanent magnet M in such a way that it can rotate freely between the
poles N and S on the shaft.
2. The coils AB and CD of the coil are kept perpendicular to the
direction of magnetic field between the poles of the magnet.
3. A device which reverses the direction of current through a
circuit is called a commutator (or split ring).
4. The two ends of the coil are soldered permanently to the
two half rings X and Y of a commutator.
5. A commutator is a copper ring split into two parts X and Y,
these two parts are insulated from one another and mounted
on the shaft of the motor.
6. The commutator rings are mountedon the shaft of the
coil and they also rotate when the coil rotates
7. The function of commutator rings is to reverse the
direction of current flowing through the coil after
every half rotation of the coil.

78. 8. To pass in electric current to the coil, we use two carbon strips P and Q known
as brushes.
9. The battery to supply current to the coil is connected to the two carbon brushes
P and Q through a switch.
10. The function of carbon brushes is to make contact with the rotating rings of the
commutator and through them to supply current to the coil.
Construction of a Motor

80. Working of a DC Motor
1. When an electric current is passed into the rectangular coil, this current produces a
magnetic field around the coil.
2. The magnetic field of the horseshoe-type magnet then interacts with the magnetic
field of the current-carrying coil and causes the coil to rotate continuously.

81. APPLICATIONS OF ELECTRIC MOTOR
Every motor has a shaft or spindle which rotates
continuously when current is passed into it.(Into current
carrying conductors)
Electric Motor is used in:
Electric Fans
Washing Machines
Refrigerators
Mixer and Grinder
Electric Cars & many other applications

82. Lets Test Our Memory
1. What happens when a current-carrying conductor is placed in a magnetic field?
2. When is the force experienced by a current-carrying conductor placed in a magnetic
field largest?
3. In the statement of Fleming’s Left Hand Rule, what do the following represent?
i. Direction of centre finger
ii. Direction of forefinger
iii. Direction of thumb
4. Name the device which converts electrical energy into mechanical energy?
5. What is the role of split rings in an electric motor?
6. What is the function of commutator in an electric motor?

83. ELECTROMAGNETIC INDUCTION
Electricity from Magnetism

84. ELECTROMAGNETIC INDUCTION
The production of Electricity from Magnetism is called
Electromagnetic Induction

85. How?

86. Notes
➢The current produced by moving a straight wire in a magnetic field is
called Induced Current
➢The phenomenon of Electromagnetic Induction was discovered by a British
scientist Michael Faraday and an American scientist Joseph Henry
independently in the year 1831
➢The process of Electromagnetic Induction led to the construction of
generators for producing electricity at power stations
➢A Galvanometer is an instrument which can detect the presence of electric
current in a circuit
When an electric current passes through the Galvanometer, then its
pointer deflects either to the left side of zero mark or to the right side of the
zero mark, depending on the direction of current.

87. Observations of Faraday & Henry about EMI
➢A current is induced in a coil when it is moved relative to a fixed magnet
➢A current is also induced in a fixed coil when it is moved relative to the fixed coil
➢No current is induced in a coil when the coil and magnet both are stationary relative
to one another
➢When the direction of motion of coil is reversed, the direction of current induced in
the coil also gets reversed
➢The magnitude of current induced in the coil can be increased :
○ by winding the coil on a shaft iron core
○ by increasing the number of turns in the coil
○ by increasing the strength of magnet, and
○ by increasing the speed of rotation of coil (or magnet)

88. Fleming’s Right-Hand Rule
For the direction of Induced Current

89. Fleming’s Right-Hand Rule

90. Statement
Hold the thumb, the forefinger and the centre finger of your
right-hand at right angles to one another.
Adjust your hand in such a way that forefinger points in the
direction of magnetic field, and thumb points in the
direction of motion of conductor, then the direction in
which centre finger points, gives the direction of induced
current in the conductor

91. The electrical generator is a machine for producing electric
current or electricity.
This electric generator converts mechanical energy into electrical
energy
Example
Electric Generator
Dynamo

92. Principle of Electric Generator
Electric Generator is an application of EMI

93. GENERATORS
AC GENERATORDC GENERATOR
The difference between DC & AC Generators is in their
construction

95. Domestic Electric Circuits
Domestic Wiring

96. At the end of Sources of Energy