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Electromagnetic Induction

Multiple Choice Questions

1.

Lenz's law is based on the principle of conservation of

• mass

• charge

• momentum

• energy

2.

Two similar coils are kept mutually perpendicular such that their centres coincide. At the centre, find the ratio of the magnetic field due to one coil and the resultant magnetic field through both coils, if the same current is flown.

• $1:\sqrt{2}$

• 1:3

• 1:2

• $\sqrt{3}:1$

3.

A circular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800 revolutions per minute in the earth's magnetic field (B=0.5 gauss), the emf induced in coil will be

• 1.158 V

• 0.58 V

• 0.29 V

• 5.8 V

4.

Figure shown is a distribution of charges. The flux of electric field due to these charges through the surface S is

• $\frac{3\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{2\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• zero

5.

ASsertion:- A larger dry cell has higher emf.

Reason:-  The emf of a dry cell is proportional to its size.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

6.

If electron is moving from A to B in wire AB, then current induced in the coil is

• anticlockwise

• clockwise

• arbitrary direction

• no current will be induced

7.

If the current 30A flowing in the primary coil is made zero in 0.1 sec, the emf induced in the secondary coil is 1.5 volt. The mutual inductance between the coils is

• 0.05 H

• 1.05 H

• 0.1 H

• 0.2 H

8.

If the flux associated with a coil varies at the rate of 1wb/min the induced emf is

• zero

• 6oV

• $\frac{1}{60}\mathrm{V}$

• 1V

9.

Two similar coils are kept mutually perpendicular such that their centres coincide. At the centre, find the ratio of the magnetic field due to one coil and the resultant magnetic field through both coils, if the same current is flown :

• 1 : $\sqrt{2}$

• 1 : 2

• 2 : 1

• $\sqrt{3}$ : 1

10.

Assertion:  We use a thick wire in the secondary of a step down transformer to reduce the production heat.

Reason:  When the plane of the armature is parallel to the line of force of magnetic field, the magnitude of induced e.m.f. is maximum.

• If both the assertion and reason are true and reason is a correct explanation of the assertion

• If both assertion and reason are true but assertion is not a correct explanation of the assertion.

• If the assertion is true but the reason is false.

• If both assertion and reason are false