Moving Charges and Magnetism · Question 20

In the product F = q ( v B ) = q v (B i + B j + B0 k ) For q = 1 and v = 2 i + 4 j + 6 k and F = 4 i - 20 j + 12 k What will be the complete expression for B?

1. 6 i + 6 j - 8 k
2. -8 i - 8 j - 6 k
3. -6 i - 6 j - 8 k
4. 8 i + 8 j - 6 k

A uniform conducting wire of length 12a and resistance 'R' is wound up as a current carrying coil in the shape of, (i) an equilateral triangle of side 'a' (ii) A square of side 'a' The magnetic dipole moments of the coil in each case respectively are :

1. 4Ia2 and 3Ia2
2. 3 Ia2 and 3Ia2
3. 3Ia2 and Ia2
4. 3Ia2 and 4Ia2

A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the centre of the solenoid is : ( 0 = 4 10-7 T m A-1)

1. 3.14 10-4 T
2. 6.28 10-5 T
3. 3.14 10-5 T
4. 6.28 10-4 T

A cylindrical conductor of radius R is carrying a constant current. The plot of the magnitude of the magnetic field B with the distance d from the centre of the conductor, is correctly represented by the figure :

1. [figure]
2. [figure]
3. [figure]
4. [figure]

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