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41.

Two concentric coils each of radius equal to 2 $\mathrm{\pi}$ cm are placed at right angles to each other. If 3A and 4A are the currents flowing through the two coils respectively. The magnetic induction (in Wb m^{-2}) at the centre of the coils will be

5 × 10

^{-5}12 × 10

^{-5}7 × 10

^{-5}10

^{-5}

42.

Two coils have a mutual inductance 0.005 H. The current changes in the first coil according to the equation I = i_{m} sin ωt, where i_{m} = 10 A and ω = 100 rad s^{-1}. The maximum value of the emf induced in the second coil is

$\mathrm{\pi}$

$2\mathrm{\pi}$

$4\mathrm{\pi}$

$5\mathrm{\pi}$

43.

A wheel with 10 spokes each of length L m is rotated with a uniform angular velocity ω in a plane normal to the magnetic field B. The emf induced between the axle and the rim of the wheel is

$\frac{1}{2}{\mathrm{N\omega BL}}^{2}$

$\frac{1}{2}{\mathrm{\omega BL}}^{2}$

${\mathrm{\omega BL}}^{2}$

NωBL

^{2}

44.

When 100 V DC is applied across a coil, a current of 1 A flows through it. When 100 V AC of50 Hz is applied to the same coil only 0.5 A flows. The inductance of the coil is

5.5 mH

0.55 mH

55 mH

0.55 H

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An aluminium ring B faces an electromagnet A. The current I through A can be altered. Then which of the following statements is correct ?

If I decreases, A will repel B

Whether I increases or decreases, B will not experience any force

If I increases, A will repel B

If I increases, A will attract B

C.

If I increases, A will repel B

If I increases then magnetic field in coil will be increases and $\overrightarrow{\mathrm{B}}$ will acts as shown in ring B, I will induce in such away that will opposes the increases of I in electromagnet. Hence in B direction of $\overrightarrow{\mathrm{B}}$ will be as shown. Hence repel B.

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