Moving Charges And Magnetism

A particle of mass M and charge Q moving with velocity $\overrightarrow{\mathrm{v}}$ describes a circular path of radius R when subjected to a uniform transverse magnetic field of induction B. The work done by the field when the particle completes one full circle is.

• $\left(\frac{{\mathrm{Mv}}^2}{\mathrm{R}}\right)2\mathrm{\pi R}$

• zero

• BQ 2$\mathrm{\pi }$R

• BQv 2$\mathrm{\pi }$R

The sensitiveness of a moving coil galvanometer can be increased by decreasing the

• number of turns in the coils

• area of the coil

• magnetic field

• couple per unit twist of the suspension

The earth's magnetic induction at a certain point is 7 x 10^-5 Wb/m². This is to be annuled by the magnetic induction at the centre of a circular conducting loop of radius 5 cm. The required current in the loop is

• 0.56 A

• 5.6 A

• 0.28 A

• 2.8 A

Susceptibility of a magnetic field is

• $\mathrm{{\rm X}} = \frac{\mathrm{l}}{\mathrm{H}}$

• $\mathrm{{\rm X}} = \frac{\mathrm{B}}{\mathrm{H}}$

• $\mathrm{{\rm X}} = \frac{\mathrm{M}}{\mathrm{V}}$

• $\mathrm{{\rm X}} = \frac{\mathrm{M}}{\mathrm{H}}$

An electron is moving with velocity v in the direction of magnetic field B, then force acting on electron is

• zero

• e (v x B)

• e (B x v)

• 200 J

A wire carrying current i and other carrying is in the same direction produce a magnetic  field B at the midpoint. What will be the field when 2i current is switched off ?

• B/2

• 2B

• B

• 4B

Two particles A and B of masses m and 2m have charges q and 2q respectively. Both  particles moving with velocities v₁ and v₂ respectively in the same direction and enter the same magnetic field B acting normally to their direction of motion. If the two forces F_A and F_B acting on them are in the ratio of 1 : 2, the ratio of their velocities is

• 2 : 1

• 3 : 2

• 2 : 3

• 1 : 1

A narrow beam of protons and deuterons, each having the same momentum, enters a  region of uniform magnetic field directed perpendicular to their direction of momentum. The ratio of the radii of the circular paths described by them is

• 2 : 5

• 3 : 2

• 2 : 3

• 1 : 1

A horizontal overhead power line carries a current of 90 A in east to west direction. The magnitude and direction of the magnetic field due to the current 1.5 m below the line is

• 2.5 x 10^-5 T towards north

• 3 x 10^-5 T towards east

• 1.2 x 10^-5 T towards south

• 1 x 10^-5 T towards west

A galvanometer has a resistance of 30 Q. It gives full scale deflection with a current of 2mA. Calculate, the value of the resistance needed to convert it into an ammeter of range 0 − 0.3 A. The value of the resistance needed to convert galvanometer into ammeter

• 0.2 Ω

• 0.3 Ω

• 0.4 Ω

• 0.52 Ω