41.

An electric bulb marked 40 W and 200 V, is used in a circuit of supply voltage 100 V. Now its power is

• 100 W

• 20 W

• 40 W

• 10 W

The magnetic needle of a tangent galvanometer is deflected at an angle 30° due to a magnet. The horizontal component of earth's magnetic field 0.34 x 10^-4 T is along the plane of the coil. The magnetic intensity is

• 1.96 × 10^-4 T

• 1.96 × 10⁴ T

• 1.96 × 10^-5 T

• 1.96 × 10⁵ T

The coefficient of mutual inductance, when magnetic flux changes by 2 x 10^-2 Wb and current changes by 0.01 A is

• 2 H

• 4 H

• 3 H

• 8 H

Velocity of light is equal to

• $\sqrt{{\mathrm{\epsilon }}_{\mathrm{o}} {\mathrm{\mu }}_{\mathrm{o}}}$

• $\sqrt{\raisebox{1ex}{${\mathrm{\epsilon }}_{\mathrm{o}}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{\mu }}_{\mathrm{o}}$}\right.}$

• ε_o/ μ_o

• $\sqrt{\frac{1}{{\mathrm{\epsilon }}_{\mathrm{o}} {\mathrm{\mu }}_{\mathrm{o}}}}$

When a wire is stretched and its radius becomes r/2, then its resistance will be

• 16 R

• 2R

• 4R

• 0

Assertion: The quantity L/R  possesses dimension of time. 

Reason: To reduce the rate of increase of current through a solenoid, we should increase the time constant  ( L/R ).

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

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

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

• If both assertion and reason are false.

Assertion: In a simple battery circuit, the point of the lowest potential is positive terminal of the battery. 

Reason:  The current flows towards the point of the higher potential, as it does in such a circuit from the negative to the positive terminal.

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

• If both the assertion and reason are true and reason 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.

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

Assertion:  We cannot think of a magnetic field configuration with three poles. 

Reason:  A bar magnet does exert a torque on itself due to its own field.

• 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

Assertion:  Faraday's laws are consequences of conservation of energy. 

Reason: In a purely resistive A.C. circuit, the current lags behind the e.m.f. in phase.

• 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.