191.

A long solenoid of diameter 0.1 m has 2 × 104 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0 A from 4 A in 0.05 s. If the resistance of the coil is 10π2 Ω, the total charge flowing through the coil during this time is

• 32 πμC

• 16 μC

• 32 μC

• 32 μC

Current sensitivity of a moving coil galvanometer is 5 div/mA and its voltage sensitivity (angular deflection per unit voltage applied) is 20 div/V. The resistance of the galvanometer is

• 40 Ω

• 25 Ω

• 500 Ω

• 250 Ω

A metallic rod of mass per unit length 0.5 kg m^–1 is lying horizontally on a smooth inclined plane which makes an angle of 30° with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is

• 7.14 A

• 5.98 A

• 11.32 A

• 14.76 A

The turns of a solenoid, designed to provide a given magnetic flux density along its axis, are wound to fill the space between two concentric cylinders of fixed radii. How should the diameter d of the wire used be chosen so as to minimize the heat dissipated in the windings?

• Wire should be multiple of 5d

• Wire should be multiple of d/3

• the wire is independent of d

• Can't say

A long straight wire is carrying current I in the +z direction. The x-y plane contains a closed circular loop carrying current I₂ and not encircling the straight wire. The force on the loop will be

• $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_1{\mathrm{I}}_0}{2\mathrm{\pi }}$

• $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_1{\mathrm{I}}_0}{4\mathrm{\pi }}$

• zero

• Depends on the distance of the centre of the loop from the wire.

To reduce the range of voltmeter, its resistance needs to be reduced. A voltmeter has resistance Ro and ranges V. Which of the following resistances when connected in parallel will convert it into a voltmeter of range V/n?

• nR₀

• (n+1)R₀

• (n-1)R

• None of these

A charged particle is suspended equillibrium in a uniform vertical electric field of intensity 2000V/m. If mass of the particle is 9.6×10^-16 kg, the charge on it and excess number of electrons on the particle respectively are (g=10m/s²)

• 4.8×10^-19 C,3

• 5.8×10^-19 C,4

• 3.8×10^-19C, 2

• 2.8×10^-19 C, 1

A proton enters a magnetic field of intensity 1.5 Wb/m² with a velocity 2×10⁷ m/s in a direction at angle 30^o with the field. The force on the proton will be (charge on proton is 1.6×10^-19 C)

• 2.4×10^-12 N

• 4.8×10^-12 N

• 1.2×10^-12 N

• 7.2×10^-12 N

20 ampere current is flowing in a long straight wire. The intensity of magnetic field at a distance 10 cm from the wire will be

• 2×10^-5 Wb/m²

• 9×10^-5 Wb/m²

• 4×10^-5 Wb/m²

• 6×10^-5 Wb/m²

The resistance of a galvanometer is 50 Ω. When 0.01A current flows in it, full scale deflection is obtained in galvanometer, the resistance of shunt connected to convert galvanometer into an ammeter of range 5A, will be

• 0.1 Ω

• 0.2 Ω

• 0.3 Ω

• 0.4 Ω