Moving Charges and Magnetism

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

In Thomson mass spectrograph, if E B, then the velocity of electron beam will be

1. | E|| B|
2. E B
3. | B|| E|
4. E2 B2

The magnetic field at centre, P will be [figure]

1. 04
2. 0
3. 02
4. 4 0