# Case Study Chapter 6 Electromagnetic Induction Class 12 Physics

Please refer to below Case Study Chapter 6 Electromagnetic Induction Class 12 Physics. These Case Study Questions Class 12 Physics will be coming in your examinations. Students should go through the Chapter 6 Electromagnetic Induction Case Study based questions in their Class 12 Physics CBSE, NCERT, KVS book as this will help them to secure more marks in upcoming exams.

## Case Study Based Questions Physics Class 12 – Chapter 6 Electromagnetic Induction

Motional emf from Lorentz Force. The emf induced across the ends of a conductor due to its motion in a magnetic field is called motional emf. It is produced due to the magnetic Lorentz force acting on the free electrons of the conductor. For a circuit shown in figure, if a conductor of length l moves with velocity V in a magnetic field B perpendicular to both its length and the direction of the magnetic filed, then all the induced parameters are possible in the circuit.

Question. Direction of current induced in a wire moving in a magnetic field is found using
(a) Fleming’s left hand rule
(b) Fleming’s right hand rule
(c) Ampere’s rule
(d) Right hand clasp rule

B

Question. A conducting road of length l is moving in a transverse magnetic field of strength B with velocity V. The resistance of the rod is R. The current in the rod is

A

Question. A 0.1 m long conductor carrying a current of 50A is held perpendicular to a magnetic field of 1.25 mT. The mechanical power required to move the conductor with a speed of 1 m s-1 is
(a) 62.5 mW
(b) 625 mW
(c) 6.25 mW
(d) 12.5 mW

C

Question. A bicycle generator creates 1.5 V at 15 km/hr. The emf generated at 10 km/hr is
(a) 1.5 volts
(b) 2 volts
(c) 0.5 volts
(d) 1 volt

D

Question. The dimensional formula for emf ε in MKS system will be
(a) ML2T–3A-1
(b) [ML2T-1A]
(c) ML2A
(d) [MLT-2A-2]

A

Lenz’s law states that direction of induced current in a circuit is such that it opposes the change which produces it. Thus, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that a magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flows in such a direction so as to create a magnetic flux in the direction of the original flux.

Question. Which of the following statement is correct?
(a) The induced emf is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces it.
(b) The relative motion between the coil and magnet produces change in magnetic flux.
(c) Emf is induced only if the magnet is moved towards coil.
(d) Emf is induced only if the coil is moved towards magnet.

B

Question. The polarity of induced emf is given by
(a) Ampere’s circuital law
(b) Biot-Savart law
(c) Lenz’s law
(d) Fleming’s right hand rule

C

Question. Lenz’s law is a consequence of the law of conservation of
(a) charge
(b) mass
(c) momentum
(d) energy

D

Question. Near a circular loop of conducting wire as shown in the figure, an electron moves along a straight line. The direction of the induced current if any in the loop is
(a) variable
(b) clockwise
(c) anticlockwise
(d) zero

B

Question. Two identical coils A and B are kept in a horizontal tube side without touching each other. If the current in the coil A increases with time, in response, the coil B
(a) is attracted by A
(b) remains stationary
(c) is repelled
(d) rotates

C

Mutual inductance. Mutual inductance is the phenomenon of inducing emf in a coil, due to a change of current in the neighbouring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of two coils, their geometry and relative separation between them. Mutual inductance between the two coils increase μr times if the coils are wound over an iron core of relative permeability μr.

Question. A short solenoid of radius a, number of turns per unit length n1, and length L is kept coaxially inside a very long solenoid of radius b, number of turns per unit length n2. What is the mutual inductance of the system?
(a) μ0πb2n1n2L
(b) μ0πa2n1n2L2
(c) μ0πa2n1n2L
(d) μ0πb2n1n2L2

C

Question. If a change in current of 0.01 A in one coil produces a change in magnetic flux of 2 × 10-2 weber in another coil, then the mutual inductance between coils is
(a) 0
(b) 0.5 H
(c) 2 H
(d) 3 H

D

Question. Mutual inductance of two coils can be increased by
(a) decreasing the number of turns in the coils
(b) increasing the number of turns in the coils
(c) winding the coils on wooden cores
(d) none of these.

B

Question. When a sheet of iron is placed in between the two co-axial, then the mutual inductance between the coils will
(a) increase
(b) decrease
(c) remains same
(d) cannot be predicted

A

Question. The SI unit of mutual inductance is
(a) ohm
(b) mho
(c) henry
(d) none of these

C

Eddy Current and their effects. Currents can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such current flow in the form of irregularly shaped loops throughout the body of the metal. These current look like eddies or whirlpools in water so they are known as eddy current. Eddy current have both undesirable effects and practically useful application. For example it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers.

Question. The working of speedometers of trains is based on
(a) wattless currents
(b) eddy currents
(c) alternating currents
(d) pulsating currents

B

Question. Identify the wrong statement.
(a) Eddy current are produced in a steady magnetic field.
(b) Induction furnace uses eddy currents to produce heat.
(c) Eddy currents can be used to produce braking force in moving trains.
(d) Power meters work on the principle of eddy currents.

A

Question. Which of the following is the best method to reduce eddy currents?
(a) Laminating core
(b) Using thick wires
(c) By reducing hysteresis loss
(d) None of these

A

Question. The direction of eddy currents is given by
(a) Fleming’s left hand rule
(b) Biot-Savart law
(c) Lenz’s law
(d) Ampere-circuital law

C

Question. Eddy current can be used to heat localised tissues of the human body. This branch of medical therapy is called
(a) Hyperthermia
(b) Diathermy
(c) Inductothermy
(d) None of these

B

Self Induction. When a current I flows through a coil, flux linked with it is φ = LI, where L is a constant known as self inductance of the coil.

Any charge in current sets up an induced emf in the coil. Thus, self inductance of a coil is the induced emf set up in it when the current passing through it changes at the unit rate. It is a measure of the opposition to the growth or the decay of current flowing through the coil. Also, value of self inductance depends on the number of turns in the solenoid, its area of cross-section and the permeability of its core material

Question. The inductance in a coil plays the same role as
(a) inertia in mechanics (b) energy in mechanics
(c) momentum in mechanics
(d) force in mechanics

A

Question. A current of 2.5 A flows through a coil of inductance 5 H. The magnetic flux linked with the coil is
(a) 0.5 Wb
(b) 12.5 Wb
(c) zero
(d) 2 Wb

B

Question. The inductance L of a solenoid depends upon its radius R as
(a) L ∝ R
(b) L ∝ 1/R
(c) L ∝ R2
(d) L ∝ R3

C

Question. The unit of self-inductance is
(a) Weber ampere
(b) Weber-1 ampere
(c) Ohm second