Moving Charges and Magnetism

A galvanometer has a coil of resistance 100 ohm and gives a full scale deflection for 30 mA current. If it is to work as a voltmeter of 30 volt range, the resistance required to be added will be

1. 900
2. 1800
3. 500
4. 1000

A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is F, the net force on the remaining three arms of the loop is

1. 3 F
2. - F
3. -3 F
4. F

A beam of cathode rays is subjected to crossed electric (E) and magnetic fields (B). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by (Where V is the potential difference between cathode and anode)

1. B22VE2
2. 2VB2E2
3. 2VE2B2
4. E22VB2

A galvanometer having a coil resistance of 60 shows full scale deflection when a current of 1.0 amp passes through it. It can be converted into an ammeter to read currents up to 5.0 amp by

1. putting in series a resistance of 15
2. putting in series a resistance of 240
3. putting in parallel a resistance of 15
4. putting in parallel a resistance of 240

The magnetic force acting on a charged particle of charge -2 C in a magnetic field of 2 T acting in y direction, when the particle velocity is (2 i + 3 j) 106 m s-1, is

1. 4 N in z direction
2. 8 N in y direction
3. 8 N in z direction
4. 8 N in -z direction

Under the influence of a uniform magnetic field, a charged particle moves with constant speed v in a circle of radius R. The time period of rotation of the particle

1. depends on R and not on v
2. is independent of both v and R
3. depends on both v and R
4. depends on v and not on R

A particle of mass m, charge Q and kinetic energy T enters a transverse uniform magnetic field of induction B. After 3 seconds the kinetic energy of the particle will be

1. T
2. 4 T
3. 3 T
4. 2 T

A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F1, F2 and F3 respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is [figure]

1. (F3 - F1)2 - F22
2. F3 - F1 + F2
3. F3 - F1 - F2
4. (F3 - F1)2 + F22

A galvanometer of resistance 50 is connected to a battery of 3 V along with a resistance of 2950 in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be

1. 6050
2. 4450
3. 5050
4. 5550

Under the influence of a uniform magnetic field, a charged particle moves with constant speed v in a circle of radius R. The time period of rotation of the particle

1. depends on R and not on v
2. is independent of both v and R
3. depends on both v and R
4. depends on v and not on R

The resistance of an ammeter is 13 and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt-resistance is

1. 2
2. 0.2
3. 2 k
4. 20

A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment is given by

1. qvR2
2. qvR2/2
3. qvR
4. qvR/2

A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move

1. in a circular orbit
2. along a parabolic path
3. along a straight line
4. in an elliptical orbit

In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant, the ratio ( charge on the ionmass of the ion ) will be proportional to

1. 1/R2
2. R2
3. R
4. 1/R

When a charged particle moving with velocity v is subjected to a magnetic field of induction B, the force on it is non-zero. This implies that

1. angle between v and B is either zero or 180
2. angle between v and B is necessarily 90
3. angle between v and B can have any value other than 90
4. angle between v and B can have any value other than zero and 180

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 )

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