Moving Charges and Magnetism · Question 31

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

A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be

1. 1.5 MeV
2. 1 MeV
3. 4 MeV
4. 0.5 MeV

A rectangular coil of length 0.12 m and width 0.1 m having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0.2 weber/m2. The coil carries a current of 2 A. If the plane of the coil is inclined at an angle of 30 with the direction of the field, the torque required to keep the coil in stable equilibrium will be

1. 0.24 Nm
2. 0.12 Nm
3. 0.15 Nm
4. 0.20 Nm

An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude

1. 0 n2 er
2. 0 n e2r
3. 0 n e2 r
4. Zero

A wire carrying current I has the shape shown in adjoining figure. [figure] Linear parts of the wire are very long and parallel to X-axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point O is

1. B = - 0 I4 R ( i + 2 k )
2. B = 0 I4 R ( i - 2 k )
3. B = 0 I4 R ( i + 2 k )
4. B = - 0 I4 R ( i - 2 k )

In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G, the resistance of ammeter will be

1. 1499 G
2. 499500 G
3. 1500 G
4. 500499 G

Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I1 and I2 currents, respectively. Point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be

1. 02 d ( I1I2 )
2. 02 d (I1 + I2 )
3. 02 d (I12 - I22 )
4. 02 d (I12 + I22 )1/2

When a proton is released from rest in a room, it starts with an initial acceleration a0 towards west. When it is projected towards north with a speed v0 it moves with an initial acceleration 3a0 towards west. The electric and magnetic fields in the room are

1. ma0e east, 3ma0ev0 up
2. ma0e east, 3ma0ev0 down
3. ma0e west, 2ma0ev0 up
4. ma0e west, 2ma0ev0 down