Electromagnetic Induction

Electromagnetic Induction Class 12 Physics MCQs

1. The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a short galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was
(a) moving towards the solenoid
(b) moving into the solenoid
(c) at rest inside the solenoid
(d) moving out of the solenoid

2. The magnetic flux linked with a coil of N turns of area of cross section A held with its plane parallel to the field B is

3. Faraday’s laws are consequence of the conservation of
(a) charge
(b) energy
(c) magnetic field
(d) both (b) and (c)

4. Two identical coaxial coils P and Q carrying equal amount of current in the same direction are brought nearer. The current in
(a) P increases while in Q decreases
(b) Q increases while in P decreases
(c) both P and Q increases
(d) both P and Q decreases

5. 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

6. Lenz’s law is a consequence of the law of conservation of
(a) charge
(b) energy
(c) induced emf
(d) induced current

7. A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, the current will
(a) increase
(b) decrease
(c) remain same
(d) first increase then decrease

8. Which of the following statements is not correct?
(a) Whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in circuit.
(b) The induced emf lasts so long as the change in magnetic flux continues.
(c) The direction of induced emf is given by Lenz’s law.
(d) Lenz’s law is a consequence of the law of conservation of momentum.

9. There is a uniform magnetic field directed perpendicular and into the plane of the paper. An irregular shaped conducting loop is slowly changing into a circular loop in the plane of the paper. Then
(a) current is induced in the loop in the anti-clockwise direction.
(b) current is induced in the loop in the clockwise direction.
(c) ac is induced in the loop.
(d) no current is induced in the loop.

10. In the given figure current from A to B in the straight wire is decreasing. The direction of induced current in the loop is A

(a) clockwise
(b) anticlockwise
(c) changing
(d) nothing can be said

11. The north pole of a bar magnet is rapidly introduced into a solenoid at one end (say A). Which of the following statements correctly depicts the phenomenon taking place?
(a) No induced emf is developed.
(b) The end A of the solenoid behaves like a south pole.
(c) The end A of the solenoid behaves like north pole.
(d) The end A of the solenoid acquires positive potential.

12. A metal plate can be heated by
(a) passing either a direct or alternating current through the plate.
(b) placing in a time varying magnetic field.
(c) placing in a space varying magnetic field, but does not vary with time.
(d) both (a) and (b) are correct.

13. Identify the wrong statement.
(a) Eddy currents are produced in a steady magnetic field.
(b) Eddy currents can be minimized by using laminated core.
(c) Induction furnace uses eddy current to produce heat.
(d) Eddy current can be used to produce braking force in moving trains.

14. Which of the following does not use the application of eddy current?
(a) Electric power meters
(b) Induction furnace
(c) LED lights
(d) Magnetic brakes in trains

15. If number of turns in primary and secondary coils is increased to two times each, the mutual inductance
(a) becomes 4 times
(b) becomes 2 times
(c) becomes A times
(d) remains unchanged 4

16. When the rate of change oic current is unity, the induced emf is equal to
(a) thickness of coil
(b) number of turns in coil
(c) coefficient of self inductance
(d) total flux linked with coil

17. Two inductors of inductance .L each are connected in series with opposite? magnetic fluxes. The resultant inductance is
(Ignore mutual inductance)
(a) zero
(b) L
(c) 2L
(d) 3L

Question 18.
The coupling co-efficient of the perfectly coupled coils is:
(a) Zero
(b) 1
(c) slightly more than 1
(d) infinite

Question 19.
1 henry is equal to :
(a) \(\frac{weber}{ampere}\)
(b) \(\frac{weber}{Volt}\)
(c) weber ampere
(d) None of these

Question 20.
The magnetic field is parallel to a surface, then the magnetic flux through the surface is :
(a) zero
(b) small but not zero
(c) infinite
(d) large but not infinite

Question 21.
In the expression e = –\(\frac{d∅}{dt}\), the -ve sign signifies:
(a) The induced emf is produced only when magnetic flux decreases
(b) The induced emf opposes the change in the magnetic flux
(c) The induced emf is opposite to the direction of the flux
(d) None of these

Question 22.
An e^– and a p^– are moving parallel to each other in a magnetic field. The magnetic force acting on the p⁺ is:
(a) 1840 times that on e^–
(b) less than that of e^–
(c) same as that of e^–
(d) slightly more than that of e^–

Question 23.
Which of the following is not equal to a henry?
(a) \(\frac{Volt second}{ampere}\)
(b) \(\frac{Volt second^2}{Coulomb}\)
(c) \(\frac{Volt^2 second}{Coulomb}\)
(d) \(\frac{Jole second}{Coulomb^2}\)

Question 24.
A transformer is used to light 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A. Then the efficiency of the transformer is:
(a) 11%
(b) 50%
(c) 80%
(d) 90%

Question 25.
The magnetic flux (∅) linked with a coil is related to the number of turns (N) ofthe coil as:
(a) f ∝ N
(b) f ∝ N^-1
(c) f ∝ N²
(d) f ∝ N^-2

Question 26.
The magnetic flux (∅) lined with a coil is related to its area (s) as:
(a) ∅ ∝ s
(b) ∅ ∝ s²
(c) ∅ ∝ s^1/2
(d) ∅ ∝ s^-1/2

Question 27.
If the magnetic flux linked with a coil through which a current off ampere is set up is ∅, then the coefficient of self-inductance of the coil is:
(a) \(\frac{l}{∅}\)
(b) \(\frac{∅}{l}\)
(c) ∅l
(d) None of these

Question 28.
In a uniform magnetic field B, a wire in the form of a semicircle of radius r rotated about the diameter of the circle with angular frequency ‘ω’. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R the mean power generated per period of rotation is :
(a) \(\frac{Bπr^2ω}{2R}\)
(b) \(\frac{(Bπr^2ω)^2}{8R}\)
(c) \(\frac{(Bπrω)^2}{2R}\)
(d) \(\frac{(Bπrω^2)^2}{8R}\)

Question 29.
The role of inductance is equivalent to:
(a) inertia
(b) force
(c) energy
(d) momentum

Question 30.
A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 rad s^-1 . If the horizontal component of earth’s magnetism is 2 × 10^-5 T, then e.m.f. developed between the two ends of the conductor is:
(a) 5 µV
(b) 50 µV
(c) 5 mV
(d) 50 mV

Question 31.
coil of L = 8.4 mH and R = 6 Ω is connected to a 12 V battery. The current in the coil is 1.0 A at approx’time of:
(a) 500 s
(b) 20 s
(c) 35 ms
(d) 1 ms

Question 32.
If I current is flowing inductance L, then the dimension of \(\frac{3}{2}\) LI² is equivalent to:
(a) charge
(b) force
(c) momentum
(d) energy

Question 33.
The phase difference between the flux linkage and the emf in a rotating coil in a uniform magnetic field is:
(a) zero
(b) \(\frac{π}{2}\)
(c) \(\frac{π}{4}\)
(d) π

Question 34.
A choke is used as a resistance in :
(a) dc circuits
(b) ac circuits
(c) both ac and dc circuits
(d) neither (a) nor (b)

Question 35.
The SI unit of magnetic flux is:
(a) T
(b) Tn^-2
(c) Wb
(d) Wb m^-2

Question 36.
For purely capacitive circuits, power factor is:
(a) 0
(b) -1
(c) 1
(d) infinity

Question 37.
The magnetic flux linked with a coil is inversely proportional to the?
(a) magnetic field
(b) area of cross section
(c) number of turns
(d) none of these

Question 38.
When the magnetic field is parallel to a surface, then the magnetic flux through the surface is:
(a) infinite
(b) zero
(c) small but not zero
(d) large but not infinite.

Question 39.
The energy stored in a 50 mH inductor carrying a current of 4 A is:
(a) 0.1 J
(b) 0.4 J
(c) 0.04 J
(d) 0.01 J

Question 40.
The flux linked with a coif at any instant t is given by ∅ = 10t² – 50t + 250. The induced emf at t = 35 is:
(a) 10 V
(b) 190 V
(c) -190 V
(d) -10 V

Question 41.
Two coils of self inductance 2 mil and 8 mil are placed so close together that the effective flux in one coil is completely linked with other. The mutual inductance between these coils is :
(a) 4 mH
(b) 16 mH
(c) 10 mH
(d) 6 mH

Question 42.
The core of a transformer is laminated because:
(a) rusting of core may be prevented
(b) ratio of voltage in primary and secondary may be increased.
(c) energy losses due to eddy current may be minimised
(d) The weight of transformer may be reduced