1. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES

2. By the end of lesson, you will able to:
 State what an electromagnet is.
 Draw the magnetic field pattern due to a
current in a:
a) straight wire
b) coil
c) solenoid
 Factors affecting the strength of magnetic
field of an electromagnet.
 Describe applications of electromagnets.

3.  An electromagnet is a temporary magnet
when current is passed through the wire
winding a soft iron core.

4.  The pattern of magnetic field depends on
shape of the conductor.
 The direction of magnetic field depends on
direction of the current.

5.  A magnetic field pattern can be represented by field
lines that show the shape of the field.
Current flow

6.  The right-hand grip rule

8.  At the centre of the
coil:
 The magnetic field is
the strongest
because magnetic
field lines are close
together
 The field patterns is
straight at right
angle

11. The direction of
magnetic field
inside the solenoid The pattern of the
is opposite to the magnetic field of a
direction outside solenoid is similar
solenoid. to that of a bar
magnet.

12.  The thumb points
towards north pole
of the magnetic
field.
 Other fingers
indicate the
direction of the
Right hand grip
current in the
rule for solenoid
solenoid.

13. Draw a magnetic field pattern and direction
N S

15. Electric bell Magnetic
relay
Telephone Circuit
earpiece breaker

18. Soft iron armature
Current flow attracted towards the
through magnetic iron core and Spring return the
solenoid 1 disconnects from the iron armature to its
when switch contact. original position
is pressed. 3 and circuit closed
6 again.
Soft iron core
in solenoid
become
2 Contact
5) Circuit is
electromagnet 5 open and no
.
current flows
and
electromagnet
lose it
magnetism.
4
Hammer hits the gong
very quickly to produce
sound.

19.  Use as a switch to
turn on high
voltage appliances
such as air
conditioner to
prevents direct
contact with
human.

20. Current flow through high The bottom of spring
voltage at 2nd circuit. contact is bent upwards
5 4
Spring contact
3
The iron armature
attracts towards
electromagnet .
2
The iron core magnetised to become
electromagnet.
1
When 1st switch is closed, current
flow in solenoid.

23. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES

24. By the end of lesson, you will able to:
 Describe what happens to a current-carrying conductor in a
magnetic field.
 Draw the pattern of the combined magnetic field due to a
current-carrying conductor in a magnetic field.
 Describe how a current-carrying conductor in a magnetic
field experiences a force.
 Explain the factors affecting magnitude of force.
 Describe how a current-carrying coil in a magnetic field
experiences a turning force.
 Describe how a direct current motor works.
 State factors affect the speed of rotation of an electric
motor.

25.  A magnetic force is produced when a current- carrying
conductor is in a magnetic field.

26.  The direction of
magnetic force, F
acting on the
wire can be
determine by
using Fleming’s
Left-hand Rule.

27. -
N +
S
By using Fleming’s Left-hand Rule, determine:
 Flow of current
 Direction of magnetic field
 Direction of magnetic force

28. N Direction of current
Direction of Force
S

29. N
Direction of Force Direction of current
S

30. S
Direction of current
Direction of Force
N

31. S
N
 The direction of magnetic field is parallel to the
direction of current.
 The short wire stays at rest.

32.  When current-carrying conductor is in a magnetic
field of permanent magnet, the interaction between
two magnetic field produce a force on the conductor.
 The direction of magnetic field, the direction of
current and direction of force are perpendicular to
each other.
Direction of force
Direction of
magnetic field
Direction of current

33. 1. Permanent 2. Current-carrying 3. The two field
magnet produced conductor interact to
a uniform, parallel produced a produced a
magnetic field. circular magnetic resultant
field. magnetic field.
N S N S

34.  The two field interact to produced a resultant magnetic
field known as Catapult Field.
Region of weaker
magnetic field
- 2 fields act in opposite
direction
Region of strong The interaction between
magnetic field two magnetic field
- 2 fields act in the produce a force on the
same direction. conductor

36. +
Magnetic Magnetic field
N S of Current-
field of
permanent carrying
magnet conductor
Region of
weaker
magnetic
field
Region of
strong
magnetic field

37. Magnetic Magnetic field
field of
permanent
N S + of Current-
carrying
magnet conductor
Region of
Region of stronger
weaker magnetic
N S
magnetic field
field - 2 fields
- 2 fields act in the
act in same
opposite direction.
direction
Direction of force Catapult field

38.  Magnitude of current
• Current can be increased by increasing the e.m.f of power
supply // using thicker wire of same length// shorter wire.
• The larger the current in conductor, the larger the force
acting on it.
 Strength of magnetic field
• Stronger magnetic field can be produced by using more
powerful magnets or by placing the magnet closer to each
other to narrow the gap between the poles of the magnets.
• The stronger the strength of magnetic field, the larger the
force acting on it.

40.  If a current carrying coil is
placed in a magnetic field,
a pair of forces will be
produced on the coil.
 This is due to the
interaction of the
magnetic field of the
permanent magnet and
the magnetic field of the
current carrying coil.

41. carrying coil.

42.  Carbon brush:
To contact with the
commutator so the current
from the battery enters the
coil.
 Spring:
Push the brush so it will
always contact with the
commutator.
 Split ring commutator:
To ensure that the forces on
the coil turn the coil in one
direction only.

43.  The direct current motor uses the turning effect on a current-
carrying coil in a magnetic field.
 Electric motor converts electrical energy to kinetic energy.

44.  Magnitude of current
The higher the magnitude of current, the higher the
speed of rotation of electric motor.
 Number of turns of the coil
The higher the number of turns of coil, the higher the
speed of rotation of electric motor.
 Strength of the magnetic field
The higher the strength of magnetic field, the higher
the speed of rotation of electric motor.

45. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES

47. Electromagnetic induction is the production
of an electric current by a changing magnetic
field.
 Induced current only
produced when there is
relative motion between the
conductor and the magnetic
field lines.

48. o Moving a straight wire • Moving a permanent
quickly across a magnet towards one end
magnetic field of a solenoid.
between two
permanent magnets.

51. a)Direction of induced current in a straight wire can
be determine by using Fleming’s right hand rule.

52. Determine the direction of current.

53. a)Direction of induced current in a solenoid can be
determine by using Lenz’s law.
Lenz’s Law:
 States that the direction of the induced
current in a solenoid is such that its magnetic
effect always oppose the change producing
it.

56.  Lenz’s law is an example of the Principle of
Conservation of Energy.
 When the magnet or solenoid is moved
against the opposing force, work is done.
 Therefore mechanical energy is converted to
electrical energy.

58. The magnitude of the induced e.m.f is directly
proportional to the rate at which the conductor
cuts through the magnetic field lines.
The size of the induced e.m.f. and thus the induced
current can be increased by:
•moving the magnet or the solenoid at a higher speed.
• increasing the number of turns on the solenoid.
• increasing the strength of the magnetic field through
the use of a stronger magnet.

60.  A generator is essentially the opposite of a motor
which converts mechanical energy to electrical
energy.

62.  The two ends of the coil are connected to two slip rings which rotate
with the coil.

63.  Coil AB move downwards and coil CD
move upwards.
 Induced current flows from D to C and
from B to A.
 In external circuit, current flows from P
to Q.
 The galvanometer deflected to the
right.
 Side AB and CD are moving parallel
to the magnetic field and thus no
induced current is produced.
 The galvanometer returns to zero.

64.  Coil CD move downwards and coil AB
move upwards.
 Induced current flows from A to B and
from C to D.
 In external circuit, current flows from Q
to P.
 The galvanometer deflected to the left.
 Side AB and CD are moving parallel
to the magnetic field and thus no
induced current is produced.
 The galvanometer returns to zero.

65. Angle of rotation/ 0
900 1800 2700 3600

67. Direct current (d.c) Alternate current (a.c)
A direct current is a current that flows An alternating current is a current
in one direction only in a circuit. which flows to and fro in two
opposite directions in a circuit.
The magnitude of a direct current It changes its direction periodically.
may be:
(a) constant
(b) changes with time