The inductance of a coil in which a current of 0.1 A increasing at the rate of 0.5 As^-1 represents a power flow of $\frac{1}{2}$ W, is

• 2 H

• 8 H

• 20 H

• 10 H

A point source of electromagnetic radiation has an average power output of 1500 W. The maximum value of electric field at a distance of 3 m from this source in Vm^-1 is

• 500

• 100

• $\frac{500}{3}$

• $\frac{250}{3}$

Electromagnets are made of soft iron because soft iron has

• low susceptibility and low retentivity

• low susceptibility and high retentivity

• high permeability and low retentivity

• high permeability and high coercivity

24.

The flux linked with a circuit is given by $\mathrm{\varphi } = {\mathrm{t}}^3 + 3\mathrm{t} - 7$.The graph between time (x-axis) and induced emf (y-axis) will be a

• straight line through the origin

• straight line with positive intercept

• parabola not through the origin

• parabola through the origin

If the self-inductance of 500 tum coil is 125 mH, then the self inductance of similar coil of 800 turns is

• 48.8 mH

• 200 mH

• 187.5 mH

• 320 mH

A copper disc of radius 0.1 m is rotated about its centre with 20 rev/s in a uniform magnetic field of 0.1 T with its plane perpendicular to the field. The emf induced across the radius of the disc is

• $\frac{\mathrm{\pi }}{20} \mathrm{V}$

• $\frac{\mathrm{\pi }}{10} \mathrm{V}$

• $20 \mathrm{\pi } \mathrm{mV}$

• $10 \mathrm{\pi } \mathrm{mV}$

A varying magnetic flux linking a coil is given by $\mathrm{\varphi } - {\mathrm{Xt}}^2$. If at time t = 3 s, the emf induced is 9 V, then the value of X is

• 0.66 Wb s^-2

• 1.5 Wb s^-2

• − 0.66 Wb s^-2

• − 1.5 Wb s^-2

A short solenoid of length 4 cm, radius 2 cm and 100 turns is placed inside and on the axis of a long solenoid of length 80 cm and 1500 turns. A current of 3 A flows through the short solenoid. The mutual inductance of two solenoids is

• 2.96 × 10^-4 H

• 5.3 × 10^-5 H

• 3.52 × 10^-3 H

• 8.3 × 10^-5 H

A coil having an inductance of 0.5 H carries a current which is uniformly varying from 0 to 10 A in 2 s. The emf (in volts) generated in the coil is

• 10

• 5

• 2.5

• 1.25

If a coil of 40 turns and area 4.0 cm² is suddenly removed from a magnetic field, it is observed that a charge of 2.0 x 10^-4 C flows into the coil. If the resistance of the coil is 80 Ω, the magnetic flux density in Wb/m² is

• 0.5

• 1.0

• 1.5

• 2.0