NCERT Class 12 MCQ Quiz Hub

1. The coupling co-efficient of the perfectly coupled coils is:
Zero
1
slightly more than 1
infinite

2. The magnetic field is parallel to a surface, then the magnetic flux through the surface is :
zero
small but not zero
infinite
large but not infinite

3. An e– and a p– are moving parallel to each other in a magnetic field. The magnetic force acting on the p+ is:
1840 times that on e–
less than that of e–
same as that of e–
slightly more than that of e–

4. 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:
11%
50%
80%
90%

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

6. The magnetic flux (∅) lined with a coil is related to its area (s) as:
∅ ∝ s
∅ ∝ s²
∅ ∝ s1/2
∅ ∝ s-1/2

7. 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:
l/∅
∅/l
∅l
None of the above

8. The role of inductance is equivalent to:
inertia
force
energy
momentum

9. 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:
5 µV
50 µV
5 mV
50 mV

10. 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:
500 s
20 s
35 ms
1 ms

11. If I current is flowing inductance L, then the dimension of 32 LI² is equivalent to:
charge
force
momentum
energy

12. The phase difference between the flux linkage and the emf in a rotating coil in a uniform magnetic field is:
zero
π/2
π/4
π

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

14. The SI unit of magnetic flux is:
T
Tn-2
Wb
Wb m-2

15. For purely capacitive circuits, power factor is:
0
-1
1
infinity

16. The magnetic flux linked with a coil is inversely proportional to the?
magnetic field
area of cross section
number of turns
None of the above

17. When the magnetic field is parallel to a surface, then the magnetic flux through the surface is:
infinite
zero
small but not zero
large but not infinite.

18. The energy stored in a 50 mH inductor carrying a current of 4 A is:
0.1 J
0.4 J
0.04 J
0.01 J

19. The flux linked with a coif at any instant t is given by ∅ = 10t² – 50t + 250. The induced emf at t = 35 is:
10 V
190 V
-190
-10 V

20. 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 :
4 mH
16 mH
10 mH
6 mH

21. The core of a transformer is laminated because:
rusting of core may be prevented
ratio of voltage in primary and secondary may be increased.
energy losses due to eddy current may be minimised
The weight of transformer may be reduced