Moving Charges and Magnetism

A current loop in a magnetic field

1. can be in equilibrium in two orientations, both the equilibrium states are unstable.
2. can be in equilibrium in two orientations, one stable while the other is unstable.
3. experiences a torque whether the field is uniform or non uniform in all orientations.
4. can be in equilibrium in one orientation.

A long straight wire carries a certain current and produces a magnetic field 2 10-4 Wb m-2 at a perpendicular distance of 5 cm from the wire. An electron situated at 5 cm from the wire moves with a velocity 107 m/s towards the wire along perpendicular to it. The force experienced by the electron will be (charge on electron 1.6 10-19 C)

1. 3.2 N
2. 3.2 10-16 N
3. 1.6 10-16 N
4. zero

A circular coil ABCD carrying a current 'i' is placed in a uniform magnetic field. If the magnetic force on the segment AB is F, the force on the remaining segment BCDA is [figure]

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

A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in uniform magnetic field. What should be the energy of an -particle to describe a circle of same radius in the same field?

1. 2 MeV
2. 1 MeV
3. 0.5 MeV
4. 4 MeV

Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2I, respectively. The resultant magnetic field induction at the centre will be

1. 5 0I2R
2. 5 0IR
3. 0I2R
4. 0IR

A millivoltmeter of 25 millivolt range is to be converted into an ammeter of 25 ampere range. The value (in ohm) of necessary shunt will be

1. 0.001
2. 0.01
3. 1
4. 0.05

An alternating electric field, of frequency , is applied across the dees (radius = R) of a cyclotron that is being used to accelerate protons (mass = m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by

1. B = m e and K = 2m 2 2R2
2. B = 2 e and K = m2 2
3. B = 2 e and K = 2m 2 2R2
4. B = m e and K = m2 2

A galvanometer of resistance, G, is shunted by a resistance S ohm. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is

1. G(S+G)
2. S2(S+G)
3. ( SGS+G )
4. G2(S+G)

Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the centre of the ring is

1. 0 qf2 R
2. 0 qf2R
3. 0 q2fR
4. 0 q2 fR

A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current I1 at a distance d from the conductor as shown in figure. The loop will experience [figure]

1. a net attractive force towards the conductor
2. a net repulsive force away from the conductor
3. a net torque acting upward perpendicular to the horizontal plane
4. a net torque acting downward normal to horizontal plane