in these notes, you will learn the basic terminologies related to magnetism or magnetic effects. Magnetism is the most important branch in the phase of physics. I explained it properly in these notes

1. Compiled by: Talha Noor (B.S Physics)
Chapter # 15
“electromegnatism”
MCQ’s
1) Who discovered left hand rule?
(a) Fleming (b) Einstein (c) Newton (d) Faraday
2) According to faraday’s law, induced e.m.f is proportional to change in flux?
(a) Inversely (b) Directly (c) Equal d) Opposite
3) Who discovered the phenomenon of electromagnetic induction?
(a) Ohm (b) Faraday (c) Coulomb (d) None
4) Types of transformer are?
(a) 1 (b)3 (c) 2 (d) 4
5) Which thing work on the principle of the electromagnetic induction in hydroelectric power house?
(a) Motor (b) Generator (c) Galvanic cell (d) Voltaic cell
6) If the current in a wire which is placed perpendicular to a magnetic field increases the force on the
wire?
(a) Increases (b) Decreases (c) Same (d) Zero
7) Which statement is true about the magnetic field?
(a) A single pole does not exit (b) like poles attract each other
(c) Magnetic pole do not effect on each other (d) Un-like poles repel each other
8) The turn ratio of a transformer is 10, it means?
(a) 10
p
s
V
V 
(b) 10
s p
N N
 (c)
10
s
p
N
N
 (d) 10
s p
I
I 
9) The presence of magnetic field can be detected by a?
(a) Small mass (b) Stationary positive charge
(c) Magnetic compass (d) Stationary Negative charge
10) Michael faraday belonged to?
(a) K.S.A (b) Russia (c) American (d) British
11) Laws of electromagnetic induction and electrolysis were presented by?
(a) Simon Ohm, (b) Michael faraday (c) George Coulomb (d) None
12) Which port of the D.C motor reverses the direction of current through the coil every half cycle?
(a) Armature (b) Slip rings (c) Commutator (d) Brushes
13) The strength of magnetic field will be maximum in a loop when the area of loop_______ to
magnetic field?
(a) At right angle (b) Perpendicular (c) Normal (d) All
14) The strength of magnetic field will be minimum in a loop when the area of loop_______ to
magnetic field?
(a) At right angle (b) Perpendicular (c) parallel (d) Both a and b

2. Compiled by: Talha Noor (B.S Physics)
Short Questions
1) State the faraday laws of electromagnetic induction.
Ans. The value of induced emf is directly proportional to the change in number of magnetic field lines
passing through it. This is called the faraday law of magnetic induction.
2) What is transfer? Explain the working of transformer in connection with mutual induction?
Ans. Transformer: Transformer is an electric device which is used to
increase or decrease the value of alternating voltage.
Principle: When the primary coil is connected to a source of A.C voltage
the changing current creates a changing magnetic field which is carried
through the core to the secondary coil. In secondary coil, the changing
field induces a varying e.m.f. This effect is called mutual inductance.
3) What do you understand by the term mutual induction? Name and define SI unit of the mutual
inductance.
Ans. Mutual Induction: “The phenomenon of production of induced
current in one coil due to change in current in neighboring coil is called
mutual induction”
Unit: Unit of mutual induction is Henry.
Henry: The mutual induction of two coil is one Henry, if the current to
changing at, the rate of one ampere per second in primary coil produces on
e.m.f of 1 Volt in secondary coil.
4) What is DC motor or electric motor? Write its principle.
Ans. Electric Motor or DC motor: Electric Motor is a device that converts electric energy into rotational
kinetic energy.
Principle of D.C motor: If instead of a straight conductor, we place a current – carrying loop inside the
magnetic field, the loop will rotate due to the torque acting on the coil. This is also called principle of D.C
motor.
5) State an easy rule by which the polarity (direction) of current carrying solenoid can be found out?
Ans. Direction of magnetic field around the current carrying solenoid can be determined by Right hand rule.
Right Hand Rule: “Grasp a solenoid with your right hand such that your Thumb pointed in the direction of
the conventional (Positive) current then curling fingers of your hand will point in the direction of magnetic
field.”
6) Describe the direction of an induced e.m.f in a circuit? How does this phenomenon relate to
conservation of energy?
Ans. Lenz’s law: The induced e.m.f is always opposite to the cause which produced it.
Lenz’s law is in accordance of Law of conservation of energy:-
When we put the wire loop in a magnetic field, work is done against the magnetic field force attraction and
doing so we feed energy to the loop this energy is source of induced current thus electromagnetic
induction is according to the law of conservation of energy.
7) Define AC generator.
Ans. AC Generator: The device which converts mechanical energy into electrical energy is called AC
generator.
8) What is relay?
Ans. Relay: Relay is a electronic switch which is used to control a large current with the help of a small
current. Relay is open and close under the control of another electrical circuit.

3. Compiled by: Talha Noor (B.S Physics)
9) Which is the principle to finding the direction of magnetic field? State it.
Ans. The direction of the force on a current carrying wire in a magnetic field can be found by using
Fleming’s Left hand rule.
Fleming’s Left Hand Rule: “Stretch the thumb, forefinger and the middle finger of the left hand mutually
perpendicular to each other. If the forefinger points in the direction of the magnetic field the middle finger in
the direction of the current, then the thumb would indicate the direction of the force acting on the
conductor.”
10) What is meant by intensity (Strength) of magnetic field? Under what condition it will be maximum
and minimum?
Ans. Intensity or Strength of magnetic field: The number of magnetic field lines passing through a unit
area is called intensity or strength of magnetic field.
Maximum: The strength of magnetic field will be maximum in a loop when the area of loop perpendicular
to magnetic field.
Minimum: The strength of magnetic field will be maximum in a loop when the area of loop parallel to
magnetic field.
11) What is the working principle of AC generator?
Ans. If a coil is rotated in a magnetic field, a current will be induced in the coil. The strength of induced
current depends upon the number of magnetic field lines passing through the coil, it will be maximum when
area of loop perpendicular to the magnetic field lines and minimum when area is parallel. Its mean the
induced current changes from minimum to maximum, maximum to minimum and vise versa.
This is the principle of AC generator.
12) State that a current – carrying coil in a magnetic field experience a torque?
Ans. If instead of a straight conductor, we place a current – carrying loop inside the magnetic field, the loop
will rotate due to torque acting on the coil. The two forces which are equal in magnitude but opposite in
direction from a couple and due to couple coil experience a torque.
13) What is the difference between a generator and a motor?
Ans.
Generator D.C Motor
 A generator is a device which is used to
convert chemical energy into electrical
energy.
 Slip rings in generator are complete. i.e. not
split into two halves.
 Coil in generator rotates completely.
 Carbon brushes are not changed.
 D.C motor is a device which is used to
convert electrical energy into mechanical
energy.
 Slip rings in D.C motor split into two halves.
They maintained the direction of current.
 Direction of current does not change.
 Carbon brushes change their place.
14) What is the difference between step up and step down transformer?
Ans.
Step-up Step-down
 It is a type of transformer which is used to
increase voltage.
 In step up transformer, the number of turns
on the secondary is greater than the number
of turns on the primary coil.
s p
N
N 
 In step up transformer, the voltage of the
 It is a type of transformer which is used to
decrease voltage.
 In step down transformer, the number of
turns on the primary is greater than the
number of turns on the secondary coil.
p s
N
N 
 In step down transformer, the voltage of the

4. Compiled by: Talha Noor (B.S Physics)
secondary is greater that the voltage of the
primary coil.
s p
V V

primary is greater that the voltage of the
secondary coil.
p s
V V

Long Questions
Q#1: Write a note on AC generator? (V. Imp)
Q#2: What is Transformer, Explain its type? (V. Imp)
Q#3: Define electromagnetic induction. And explain it with examples? (Imp)s
Q#4: State and explain mutual induction? (V. Imp)
Q#5: Write a note on DC motor? (V. Imp)
Numerical
Numerical: (All) “(15.1, 15.2, 15.3, 15.5) V. imp”
Example: 15.1