JEE Advanced (Assertion-Reason Type): Electromagnetic Induction & Alternating Current | Chapter-wise Tests for JEE Main & Advanced PDF Download

Direction: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Q.1. Assertion: Eddy currents is produced in any metallic conductor when magnetic flux is changed around it.
Reason: Electric potential determines the flow of charge.[AIIMS 1995]
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
When a metallic conductor is moved in a magnetic field; magnetic flux is varied. It disturbs the free electrons of the metal and set up an induced emf in it. As there are no free ends of the metal i.e. it will be closed in itself so there will be induced current.

Q.2. Assertion: The quantity L/R possesses dimensions of time.
Reason: To reduce the rate of increases of current through a solenoid should increase the time constant (L/R).
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
The relation of induced emf is  and current i is given by  ⇒  In order to decreases the rate of increase of current through solenoid. We have to increase the time constant L/R.

Q.3. Assertion: Faradays laws are consequences of conservation of energy.
Reason: In a purely resistive ac circuit, the current lags behind the e.m.f. in phase.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
According to Faraday's laws, the conversion of mechanical energy into electrical energy. This is in accordance with the law of conservation of energy. It is also clearly known that in pure resistance, the emf is in phase with the current.

Q.4. Assertion: Only a change in magnetic flux will maintain an induced current the coil.
Reason: The presence of large magnetic flux through a coil maintains a current in the coil if the circuit is continuous.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
Presence of magnetic flux cannot produce current.

Q.5. Assertion: Magnetic flux can produce induced e.m.f.
Reason: Faraday established induced e.m.f. experimentally.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
E.M.F. induces, when there is change in magnetic flux. Faraday did experiment in which, there is relative motion between the coil and magnet, the flux linked with the coil changes and e.m.f. induces.

Q.6. Assertion: The induced e.m.f. and current will be same in two identical loops of copper and aluminium, when rotated with same speed in the same magnetic field.
Reason: Induced e.m.f. is proportional to rate of change of magnetic field while induced current depends on resistance of wire.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
Since both the loops are identical (same area and number of turns) and moving with a same speed in same magnetic field. Therefore same emf is induced in both the coils. But the induced current will be more in the copper loop as its resistance will be lesser as compared to that of the aluminium loop.

Q.7. Assertion: Inductance coil are made of copper.
Reason: Induced current is more in wire having less resistance.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
The inductance coils made of copper will have very small ohmic resistance. Due to change in magnetic flux a large induced current will be produced in such an inductance, which will offer appreciable opposition to the flow of current.

Q.8. Assertion: Self-inductance is called the inertia of electricity.
Reason: Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
Self-inductance of a coil is its property virtue of which the coil opposes any change in the current flowing through it.

Q.9. Assertion: When two coils are wound on each other, the mutual induction between the coils is maximum.
Reason: Mutual induction does not depend on the orientation of the coils.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
The manner in which the two coils are oriented, determines the coefficient of coupling between them.
M = K². L₁L₂ When the two coils are wound on each other, the coefficient of coupling is maximum and hence mutual inductance between the coil is maximum.

Q.10. Assertion: Acceleration of a magnet falling through a long solenoid decreases.
Reason: The induced current produced in a circuit always flow in such direction that it opposes the change or the cause the produced it.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
The induced current in the ring opposes the motion of falling magnet. Therefore, the acceleration of the falling magnet will be less than that due to gravity.

Q.11. Assertion: An aircraft flies along the meridian, the potential at the ends of its wings will be the same.
Reason: Whenever there is change in the magnetic flux e.m.f. induces.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
As the aircraft flies, magnetic flux changes through its wings due to the vertical component of the earths magnetic field. Due to this, induced emf is produced across the wings of the aircraft. Therefore, the wings of the aircraft will not be at the same potential.

Q.12. Assertion: A spark occur between the poles of a switch when the switch is opened.
Reason: Current flowing in the conductor produces magnetic field.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
According to Lenzs law, induced emf are in a direction such as to attempt to maintain the original magnetic flux when a change occurs. When the switch is opened, the sudden drop in the magnetic field in the circuit induces an emf in a direction that attempts to keep the original current flowing. This can cause a spark as the current bridges the air gap between the poles of the switch. (The spark is more likely in circuits with large inductance).

Q.13. Assertion: In the phenomenon of mutual induction, self induction of each of the coils persists.
Reason: Self induction arises when strength of current in same coil changes. In mutual induction, current is changing in both the individual coils.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
Mutual inductance is the phenomenon according to which an opposing e.m.f. produce flux in a coil as a result of change in current or magnetic flux linked with a neighboring coil. But when two coils are inductively coupled, in addition to induced e.m.f. produced due to mutual induction, also induced e.m.f. is produced in each of the two coils due to self-induction.

Q.14. Assertion: Lenzs law violates the principle of conservation of energy.
Reason: Induced e.m.f., opposes always the change in magnetic flux responsible for its production.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
Lenzs Law is based on conservation of energy and induced emf always opposes the cause of it i.e., change in magnetic flux.

Q.15. Assertion: The induced emf in a conducting loop of wire will be non zero when it rotates in a uniform magnetic field.
Reason: The emf is induced due to change in magnetic flux.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
As the coil rotates, the magnetic flux linked with the coil (being ) will change and emf will be induced in the loop.

Q.16. Assertion: An artificial satellite with a metal surface is moving above the earth in a circular orbit. A current will be induced in satellite if the plane of the orbit is inclined to the plane of the equator.
Reason: The current will be induced only when the speed of satellite is more than 8 km/sec.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
When the satellite moves in inclined plane with equatorial plane (including orbit around the poles), the value of magnetic field will change both in magnitude and direction. Due to this, the magnetic flux through the satellite will change and hence induced currents will be produced in the metal of the satellite. But no current will induced if satellite orbits in the equatorial plane because the magnetic flux does not change through the metal of the satellite in this plane.

Q.17. Assertion: A bar magnet is dropped into a long vertical copper tube. Even taking air resistance as negligible, the magnet attains a constant terminal velocity. If the tube is heated, the terminal velocity gets increased.
Reason: The terminal velocity depends on eddy current produced in bar magnet.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
When the tube is heated its resistance gets increased due to which eddy currents produced in copper tube becomes weak. Hence opposing force also gets reduced and the terminal velocity of magnet gets increased.

Q.18. Assertion: A metal piece and a non-metal (stone) piece are dropped from the same height near earth's surface. Both will reach the earth's surface simultaneously.
Reason: There is no effect of earth's magnetic field on freely falling body.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
When a metal piece falls from a certain height then eddy currents are produced in it due to earth's magnetic field. Eddy current oppose the motion of piece. Hence metal piece falls with a smaller acceleration (as compared to g). But no eddy current are produced in non-metal piece, hence it drops with acceleration due to gravity. Therefore non-metal piece will reach the earth's surface earlier.

Q.19. Assertion: A transformer cannot work on dc supply.
Reason: dc changes neither in magnitude nor in direction.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
Transformer works on ac only, ac changes in magnitude as well as in direction.

Q.20. Assertion: Soft iron is used as a core of transformer.
Reason: Area of hysteresis is loop for soft iron is small.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
Hysteresis loss in the core of transformer directly proportional to the hysteresis loop area of the core material. Since soft iron has narrow hysteresis loop area, that is why soft iron core is used in the transformer.