71.

The coil in a tangent galvanometer is 16 cm in radius. If a current of 20 mA is to produce a deflection of 45°, then the number of turns wound on it, is (Take horizontal component of earth's magnetic field = 0.36 x 10^-4 T  and µ₀ = 4π x 10^-7 WbA^-1 m^-1 )

• 229

• 458

• 689

• 916

A frog can be levitated in magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as

• paramagnetic

• diamagnetic

• ferromagnetic

• anti-ferromagnetic

The magnetic susceptibility of a material of a rod is 499. The absolute permeability of vacuum is 4$\mathrm{\pi }$ x 10^-7 Hm^-1 .  The absolute permeability of the material of rod is

• $\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $2\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $3\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $4\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

A small piece of metal wire is dragged across the gap between the poles of a magnet in 0.4 s. If change in magnetic flux in the wire is 8 x 10^-4 Wb, then emf induced in the wire is

• 8 × 10^-3 V

• 6 × 10^-3 V

• 4 × 10^-3 V

• 2 × 10^-3 V

The magnetic flux linked with a coil at any instant t is given by the equation : $\mathrm{\varphi }$ = 5t³ − 100t + 300. The magnitude of emf induced in the coil after 3 s is

• 10 V

• 20 V

• 35 V

• 70 V

In 0.1 s, the current in a coil increases from 1 A to 1.5 A. If inductance of coil is 60 mH, then induced current in external resistance of 3Ω will be

• 1 A

• 0.5 A

• 0.2 A

• 0.1 A

The impedence of a circuit, when a resistance R and an inductor of inductance L are connected in series in an AC circuit of frequency f, is

• $\sqrt{\mathrm{R} + 2{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{\mathrm{R} + 4{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{{\mathrm{R}}^2 + 4{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{{\mathrm{R}}^2 + 2{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

In a series LCR circuit, resistance R = 10 Ω and the impedance Z = 10 Ω. The phase difference between the current and the voltage is

• 0°

• 30°

• 45°

• 60°

A circuit consists of an inductance of 0.5 mH and a capacitor of 20 µF. The frequency of the LC oscillations is approximately

• 400 Hz

• 88 Hz

• 1600 Hz

• 2400 Hz

Which of the following electromagnetic waves have the smallest wavelength ?

• γ-rays

• X-rays

• UV waves

• infrared rays