Moving Charges and Magnetism · Question 24

Ionized hydrogen atoms and α-particles with same momenta enter perpendicular to a constant magnetic field, B. The ratio of their radii of their paths rH : r will be :

1. 1 : 2
2. 4 : 1
3. 1 : 4
4. 2 : 1

A metallic rod of mass per unit length 0.5 kg m-1 is lying horizontally on a smooth inclined plane which makes an angle of 30 with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is

1. 7.14 A
2. 5.98 A
3. 14.76 A
4. 11.32 A

Current sensitivity of a moving coil galvanometer is 5 div/mA and its voltage sensitivity (angular deflection per unit voltage applied) is 20 div/V. The resistance of the galvanometer is

1. 40
2. 25
3. 250
4. 500

An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current 'I' along the same direction as shown in figure. Magnitude of force per unit length on the middle wire 'B' is given by [figure]

1. 2 0 I2 d
2. 2 0 I2 d
3. 0 I2 2 d
4. 0 I22 d

A 250-turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180 against the torque is

1. 4.55
2. 2.3
3. 1.15
4. 9.1

A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distance a2 and 2a respectively, from the axis of the wire is

1. 1
2. 4
3. 14
4. 12

A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be [figure]

1. 2 0 IiL3
2. 0 IiL2
3. 2 0 Ii3
4. 0 Ii2

A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be

1. nB
2. n2B
3. 2nB
4. 2n2B

An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 10-2 T. If the value of e/m is 1.76 1011 C kg-1, the frequency of revolution of the electron is

1. 1 GHz
2. 100 MHz
3. 62.8 MHz
4. 6.28 MHz

A circuit contains an ammeter, a battery of 30 V and a resistance 40.8 ohm all connected in series. If the ammeter has a coil of resistance 480 ohm and a shunt of 20 ohm, the reading in the ammeter will be

1. 2 A
2. 1 A
3. 0.5 A
4. 0.25 A