Moving Charges and Magnetism

Two circular coils 1 and 2 are made from the same wire but the radius of the 1st coil is twice that of the 2nd coil. What ratio of potential difference in volts should be applied across them so that the magnetic field at their centres is the same?

1. 2
2. 3
3. 4
4. 6

A very long straight wire carries a current I. At the instant when a charge +Q at point P has velocity v, as shown, the force on the charge is [figure]

1. along Oy
2. opposite to Oy
3. along Ox
4. opposite to Ox

An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to

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

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 )