View latest educational results 2026 of class 9th, 10th / Matric / SSC, Intermediate / HSSC / FA / FSc / Inter, 5th / Primary, 8th / Middle, DAE, DBA, D.COM, BA / BBA / BCom / BSc / B.Ed, MA / MSc / MBA / MIT / MCS, MBBA / M.Ed, LLB, Engineering, M.Phil, PhD from all BISE / boards and Universities by roll number & by name and check old result 2025 online.

Home
eLearn
12th Class
12th Class Punjab
Physics
Physics Short Question
Electromagnetic Induction Short Questions Preparation

Chapter 15 Electromagnetic Induction Physics 12th Class Punjab Short Questions

Question No. 1 - Define mutual inductance and write at least two factors at which it depends.

Answer No. 1 - The ratio of average emf induced in the secondary to the time rate of changing current in the primary is called mutual inductance.
It depends upon numbers of turn of the coil, area of cross section of the coil closeness of coil and nature of the core materials.

Question No. 2 - What is electromagnet?Mention two practical example of electromagnet.

Answer No. 2 - When a specimen of iron is placed inside a current carrying solenoid, it becomes and electromagnet. Examples are:
1. Transformers
2. Motors

Question No. 3 - What is DC motor? Write its principle.

Answer No. 3 - A DC motor is a device which converts D.C electrical energy into mechanical energy. The basic principle of electric motor is that a current carrying coil placed in magnetic field experiences a torque which is given by t=NIAB cos theta.

Question No. 4 - Define induced emf and induced current.

Answer No. 4 - If a conductor moves through a magnetic field then due to change in magnetic flux, an emf is induced across the ends of the conductor which is known as back emf. If the circuit is close it will cause an electric current which is called as induced current.

Question No. 5 - What is mean by commutator in D.C generator?

Answer No. 5 - Commutator consists of two split rings or two halves of a single ring. Each half of split ring is connected to each end of the rotating coil. It helps to maintain the output in the same direction by inverting lower halves if sine curve.

Question No. 6 - When the primary of a transformer is connected to A.C mains, the current it is very small if the secondary circuit is open. Explain.

Answer No. 6 - If the secondary circuit is open then output power will be zero. Because output power is always slightly smaller than the input power, therefore a very small value of current is being drawn by a primary coil of transformer from AC units.

Question No. 7 - When the primary of a transformer is connected to AC mains the current in it increase when secondary circuit is closed. Explain why?

Answer No. 7 - When the secondary circuit is closed the output power increase. To produce the power, transformer will draw large current from the A.C mains to increase its primary power.

Question No. 8 - Define self induction and also write its SI units.

Answer No. 8 - The phenomena in which the changing current in a coil induce an emf in itself is called the self-induction. Its SI unit is VsA-1. It is also called as HenryH.

Question No. 9 - Define the SI unit of mutual inductance.

Answer No. 9 - If current is changing at the rate of one ampere per second and the emf induced across the ends of the coil is one volt then inductance is called one Henry. Its SI units are VsA-1.

Question No. 10 - Differentiate between motor and generator.

Answer No. 10 - Motor: A motor is a device which converts electrical energy into mechanical energy.

Question No. 11 - Define self induction and mutual induction.

Answer No. 11 - The phenomena in which changing current in a coil induced a emf in itself is called self-induction.
The phenomena in which changing current in one coil induces an emf in another coil is called mutual induction.

Question No. 12 - What is back emf in motors?

Answer No. 12 - When to coil motor rotates across the magnetic field by the applied potential difference V, an emf is induced in it. The induced emf is in such a direction that opposes the emf running motor. Due to this reasons, the induced emf is called back emf of the motor. The magnitude of the back emf increase with the speed of motor.

Question No. 13 - What is back motor effect in generators?

Answer No. 13 - Back motor effect is the opposing torque produced due to the induced emf in the coil. When coil rotated a current is drawn through the coil.The magnetic field exerts two equal and opposite forces on left and right side of the current carrying coil. These forces are such that they produce a counter torque that oppose the rotational motion of the coil. This effect is known as back motor effect in generators.

Question No. 14 - Name the factor upon which the self inductance depends.

Answer No. 14 - It depends upon induced emf and time rate of change of current in the coil. It also depend upon the number of turns of the coil, its area of cross section and the core material.

Question No. 15 - A glass rod of "L" Length is moving perpendicular to the applied magnetic field P with velocity V. Explain briefly about the induced emf in it.

Answer No. 15 - Induced emf is zero as glass rod is insulator and there are no free electrons to be shifted from one extreme to the other. Therefore there will be no effect of perpendicular magnetic field. The induced emf is only produced by moving a conductor across the magnetic field.

Question No. 16 - Why is split ring is used in DC generators in place of slips rings?

Answer No. 16 - The split rings are two halves of a ring that acts as commutator. When the current in the coil is zero and is about to change direction, the split ring also changes the contacts with the carbon brushes. Therefore the output remains the same direction although the current is not constant magnitude.

Question No. 17 - A suspended magnet is oscillating freely in the horizontal plane. The oscillation are strongly damped when a metal plate is placed under the magnet. Explain why its occurs.

Answer No. 17 - The oscillating magnet produces change of magnetic flux close to it. The metal plate placed below it experiences the change the magnetic flux. As the result eddy currents are produced inside the metal. According to Lenzs law these eddy currents oppose the cause which produce it. So the oscillation of magnet are strongly damped.

Question No. 18 - What is meant by back emf? Write its SI units.

Answer No. 18 - The emf induced across the ends of a coil due to the changing current in the same coil is called self induced emf or back emf. Its SI unit is Volt V.

Question No. 19 - In a certain region the earths magnetic field points vertically down. When a plane flies due north, which wing tip is positively charged?

Answer No. 19 - When the plane flies due north in the earth magnetic field directed vertical downward, then electron will experience force in east direction. Thus west wingtip of the plane is positively charged.

Question No. 20 - What is the working principle of transformer? Explain.

Answer No. 20 - The transformer work on the principle of mutual induction between two coils. The transformer consists of two coils of copper electrically insulated from each other wound on the same iron core. The coil to which AC power is supplied is called primary and that from which power is delivered to the circuit is called secondary.

Question No. 21 - Name four methods to produce induce emf.

Answer No. 21 - An induce emf is produced in the loop if the magnetic flux through it changes.The methods to produce induced emf are:
1. A bar magnet is moved towards the coil.
2. By changing the area of the coil in a constant magnetic
field.
3. A coil of constant area is rotated in a constant
magnetic field.
4. The coil is placed in the magnetic field of an
electromagnet.

Question No. 22 - Can step up transformer increase the power level?

Answer No. 22 - No,a step up transformer can not increase the power level in actual transformer due of dissipation of energy in the coil the output power is always less than input power. Therefore a step up transformer cant increase power level.

Question No. 23 - What happen to the current of a circuit if a load resistance of the circuit is much less than the power transferred?

Answer No. 23 - The greater the load the larger the current is supplied by the generator. When the load resistance of the circuit is much less, small current is supplied by the generator.

Question No. 24 - How the power is lost due to eddy current in a transformer and how this loss can be minimized?

Answer No. 24 - The induced currents that are set up in the core of transformer in the direction perpendicular to the flux are known as eddy currents. It results in power dissipation and heating of the coral material. The insulation between lamination sheets should be perfect so as to stop the flow of eddy currents.

Question No. 25 - Distinguished between AC generator and transformer.

Answer No. 25 - AC generator: AC generator is a device which produce AC voltage by converting mechanical energy into electrical energy.

Question No. 26 - Can an electron at rest be set in motion with magnet? Explain

Answer No. 26 - No an electron at rest can not be set in motion with a magnet because at rest electrons only have electric field which can not interfere with magnetic field to cause any force which can produce motion in electrons.

Question No. 27 - How can the power losses be minimized in a transformer?

Answer No. 27 - The power can be minimized in transformer by implementing following considerations.
1. Core should be assembled from the laminated sheet of a
material whose hysteresis loop are is very small.
2. The insulation between lamination sheets should be
perfect so as to stop the flow of eddy current.
3. The resistance of the primary and secondary coils should
be kept minimum.

Question No. 28 - If area of the loop and magnetic field both are changing and still have no induced emf. Explain why?

Answer No. 28 - If the plane of the loop is kept parallel to the direction of the magnetic field, magnetic field through the coil will be zero, no emf will be induced in the loop either by changing its are or by changing the magnetic field.

Question No. 29 - What changes are required to turn the D.C motor into D.C generators?

Answer No. 29 - 1. In order to convert DC motor into DC generator the
magnetic field must be supplied by the permanent magnet
and not by electromagnet.
2. An arrangement to rotate the coil armature should be
provided and battery must be removed.

Question No. 30 - How does Lenzs law explain law of conservation of energy phenomena of electromagnetism induction?

Answer No. 30 - When a rod is moving in the magnetic field towards right, an induced current flows through the loop in anticlockwise direction. Since current carrying rod experience a magnetic force opposite to that velocity. An external force equal in magnitude and opposite in direction must be applied to keep the rod moving with constant velocity. This dragging force provides the energy for the induced current to flow. This energy is the source of induced current. Thus electromagnetic induction is exactly according to law of conservation of energy.

Question No. 31 - What changes are required to turn the D.C motors into a D.C generators?

Answer No. 31 - 1. In order to convert to convert DC motor into SC
generator, the magnetic field must be supplied by the
permanent magnet and not by electromagnet.
2. An arrangement to rotate the coil armature should be
provided and battery must be removed.

Question No. 32 - Define motional emf and write its formula.

Answer No. 32 - If a conductor moves through a magnetic field then due to change in magnet flux, an emf is induced across the ends of the conductor which is known as motional emf.
e=vBL sin theta.

Question No. 33 - Does the induced emf always act to decrease the magnetic flux through a circuit?

Answer No. 33 - Number the induced emf always oppose the cause that produce it. If the magnetic flux through the circuit is increasing then induced emf acts to decrease the magnetic flux. Its the magnetic flux through the circuit is decreasing, then induced emf acts to increase the magnetic flux.

Question No. 34 - Define electromagnetic induction.

Answer No. 34 - When a conductor is moved through a magnetic field, the electric current flow through the circuit. The emf produced in the conductor is called induced emf and the current generated is called induced current. This phenomena is known as electromagnetic induction.

Question No. 35 - Can a transformer be used with D.C? Explain.

Answer No. 35 - No As transformer works on the principle of electromagnetic induction, which is produced by A.C and not by D.C, To induced a voltage in the secondary coil it is necessary to have magnetic flux change.

Question No. 36 - Does the induced current depend on the resistance of the circuit?

Answer No. 36 - Yes the induced current depend upon the resistance of the circuit.
By ohms law
I=e/R
Thus the induced current depends on the resistance of the circuit.

Question No. 37 - Write down any one method used for the production of induced emf.

Answer No. 37 - Induced emf can be induced by electromagnetic induction. When a conductor is moved through a magnetic field the electric current flow through the circuit. The emf produced in the conductor is called induced emf and the current generated is called induced current.

Question No. 38 - Can an electric motor be used to derive and electric generator with output from the generator being used to operate the motor?

Answer No. 38 - No,it is not possible.Because if it possible, it will be a self operating system without getting energy from some external source and this is against the law of conservation of energy.

Question No. 39 - Define mutual induction.

Answer No. 39 - The phenomena in which the changing current in one coil induces an emf in another coil is called the mutual induction.

Question No. 40 - Write two similarities and two difference between motor and generator.

Answer No. 40 - Similarities:
1. Construction of a motor is similar to a generator.
2. In both,magnetic field is provided by an electromagnet.
Differences:
1. Generators convert mechanical energy into electrical
energy while motor converts electrical energy into
mechanical energy.
2. In generator,the armature coil is rotated in the
magnetic field and the current is the output. While in
motor, armature is connected to battery, which rotated
the armature.

Question No. 41 - Can DC motor be turned into DC generator? What changes are required to be done?

Answer No. 41 - Yes, a D.C motor can be converted into D.C generator. For this armature of the motor is to be coupled with some rotating body. Due to rotation, magnetic flux through the coil changes so and emf will be induced at the output. Hence the motor acts as a generator.

Question No. 42 - State the Lenzs law and define Henry.

Answer No. 42 - Lenzs Law: It states that the direction of induced current is always so as to opposite the change which cause the current.
Henry: If the current in the primary is changing at the rate of one ampere per second and the emf induced across the ends of the secondary coil is one volt then the mutual inductance is called one Henry.

Question No. 43 - State Faradays law of electromagnetic induction.

Answer No. 43 - It states that "The average emf induced in a conducting coil of N loops is equal to the negative of the rate at which the magnetic flux through the coil is changing with time".

Question No. 44 - What is D.C motor? Write down part of D.C motor.

Answer No. 44 - D.C motor is a device which converts electrical energy into mechanical energy. Main part of D.C motor are commutator, armature and permanent magnet or electromagnet.

Question No. 45 - Is it possible to change both the area of the loop and magnetic field passing through the loop and still have to induced emf in the loop? Explain briefly.

Answer No. 45 - Yes, it the plane of the loop is kept parallel to the direction of the magnetic field magnetic flux through the coil will be zero. No emf will induced in the loop either by changing its area or by changing the magnetic field.

Question No. 46 - In a transformer there is no transfer of charge from the primary to the secondary. How is then the power transferred?

Answer No. 46 - The power will be transferred because the two coils of transformer are magnetically linked i.e, the change of flux through one coil is linked with the other coil.

Previous Question

1-46

Next Question