Moving Charges and Magnetism

A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a permanent magnet such that B is in plane of the coil. If due to a current i in the triangle a torque acts on it, the side l of the triangle is

1. 2 3 ( Bi )
2. 2 ( 3Bi )1/2
3. 2 3 ( Bi )1/2
4. 1 3 Bi

A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 10-4 ampere gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of

1. 2500 as a shunt
2. 2450 as a shunt
3. 2550 in series
4. 2450 in series

To convert a galvanometer into a voltmeter one should connect a

1. high resistance in series with galvanometer
2. low resistance in series with galvanometer
3. high resistance in parallel with galvanometer
4. low resistance in parallel with galvanometer

A charged particle moves through a magnetic field in a direction perpendicular to it. Then the

1. speed of the particle remains unchanged
2. direction of the particle remains unchanged
3. acceleration remains unchanged
4. velocity remains unchanged

A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is

1. B/2
2. B
3. 2B
4. 4B

To convert a galvanometer into a voltmeter one should connect a

1. high resistance in series with galvanometer
2. low resistance in series with galvanometer
3. high resistance in parallel with galvanometer
4. low resistance in parallel with galvanometer.

A charge q moves in a region where electric field and magnetic field both exist, then force on it is

1. q ( v B )
2. q E + q ( v B )
3. q E + q ( B v )
4. q B + q ( E v )

The magnetic field of given length of wire for single turn coil at its centre is B then its value for two turns coil for the same wire is

1. B/4
2. B/2
3. 4B
4. 2B

If number of turns, area and current through a coil is given by n, A and i respectively then its magnetic moment will be

1. niA
2. n2iA
3. niA2
4. ni A

An electron having mass m and kinetic energy E enters a uniform magnetic field B perpendicularly, then its frequency will be

1. eEqvB
2. 2 meB
3. eB2 m
4. 2meBE