12 physics EMI test

 Physics Test  class -12 Electromagnetic induction 

1) Lenz’s law is consequence of the law of conservation of-

A) charge             B) mass 

C) momentum.           D) energy 

2) 1 Henry is equal to- 

A) 1 weber/ Ampere.         B) 1 weber/ volt

C) 1 weber-Ampere.           D) 1 weber- volt

3) In a circular conducting coil, when current increases from 2A  to 18 A  in 0.05 second, then induced EMF is 20 V. The self inductance of coil is- 

A) 6.25 mH.            B) 62.5 mH

C) 50 mH.             D) None. 

4) A coil has 2000 turns and area of 70 cm². The magnetic field perpendicular to the plane of the coil is 0.3 Webber per metre square and takes 0.1s to rotate through 180°. The value of the induced EMF will be- 

A) 8.4 V.          B) 84V 

C) 42 V.             D) 4.2 V 

5) A 2 m long wire is moving in a magnetic field of 0.5 Weber per metre square in a perpendicular manner with a velocity of 1 m/s. The induced EMF will be- 

A) 0.5V.         B) 0.1 V  

  C) 1 V              D) 2V 

6) The self inductance of a coil is L. Keeping the length and area constant, the number of turns is increased by four times. The self inductance of the coil will be- 

A) 1/ 4L.        B) L 

C) 4L.             D) 16L 

7) Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area equal to 10 cm² and length equal to 20 cm. If one of the solenoid has 300 turns and the other 400 turns, their mutual inductance is- 

A) 2.4 π x 10^-4 H.         B) 2.4 πx 10^-5H 

C) 4.8 π x 10^-4H.          D) 4.8 π x10^-5 H 

8) At 10 m long copper wire while remaining in the east west horizontal direction is falling down with a speed of 5 m/s. If the horizontal component of earth’s magnetic field equal to 0.3×10 to the power -4 Weber per metre square, than the EMF developed between the ends of the wire is- 

A) 0.15 V.        B) 1.5 V 

C) 0.15 mV.       D) 1.5 mV 

9) A circular coil of 500 turns has in area of 0.1 m². It is kept perpendicular to a magnetic field of 0.2 T. The coil is rotated about the diameter by 180° for 0.1 second. If the coil is connected to the galvanometer, then how much charge will flow through it, the resistance of the circuit is 50 Ohm. 

A) 0.2 C.        B) 0.4C.       C) 2C.       D) 4C 

10) There are two coils A and B as shown in figure. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counter clockwise. B is kept stationary when A moves. We can infer that

a) there is a constant current in the clockwise direction in A.
(b) there is a varying current in A.
(c) there is no current in A.
(d) there is a constant current in the counter clockwise direction in A.

11) A metal plate is getting heated. It can be because

a) a direct current is passing through the plate
(b) it is placed in a time varying magnetic field
(c) it is placed in a space varying magnetic field, but does not vary with time 
(d) a current (either direct or alternating) is passing through the plate

12) Assertion- If a straight wire is moved in a magnetic field, no emf will be induced across its two ends as the circuit is not closed. 

Reason- since circuit is not closed, there will be non-zero current in it. 

13) Assertion : Lenz’s law violates the 

principle of conservation of energy. 

Reason : Induced e.m.f., opposes 
always the change in magnetic flux 
responsible for its production. 

14) Assertion :Inductance coil are 
made of copper

Reason :Induced current is more in 
wire having less resistance. 

15) A square of side L metres lies in the x-y plane in a region, where the magnetic field is given by B = B0{li + 3j + 4k) T, where Bo is constant. The magnitude of flux passing through the square is 

A) a) 2BoL² Wb.

(b) 3BoL² Wb.
(c) 4BoL² Wb.
(d) √29 BoL² Wb.

16 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)  B π r² w/ 2R 
(b) ( B π r² w)² /8R

(c)  ( B π r w² )² / 8R 

(d)  ( B π r w) ² /2R(𝐵π𝑟ω2)28𝑅

17 Two coils are placed close to each other. The mutual inductance of pair of coils depends upon -

A) Rate at which current change in two coils

B)  Relative position and orientation of the two coils 

C) the material of the wires of the coil

D) the currents in two coils.

18  Assertion: The presence of large magnetic flux through a coil maintains a current in the coil if the circuit is continuous.

Reason: magnetic flux is essential to maintain an induced emf