﻿ Two concentric coils each of radius equal to 2 π 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 | Electromagnetic Induction

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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 be5 × 10-5 12 × 10-5 7 × 10-5 10-5

A.

5 × 10-5

Given,  I1 = 3 A

I2 = 4 A

R = 2 $\mathrm{\pi }$ cm = 2$\mathrm{\pi }$ × 10-2 m

We know that, magnetic field of a coil,

Similarly,

Now, net magnetic field at centre of a coil,

42.

Two coils have a mutual inductance 0.005 H. The current changes in the first coil according to the equation I = im sin ωt, where im = 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

• ${\mathrm{\omega BL}}^{2}$

• NωBL2

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

45.

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