Moving Charges & Magnetism | MCQs Quiz-01

A long straight wire of radius 'a' carries a steady current 'I'. The current is uniformly distributed across its area of cross-section. The ratio of magnitude of magnetic field B₁ at distance a/2 and B₂ at distance 2a from the axis of wire is-

Assertion- The deflecting torque acting on a current carrying loop is zero when its plane is perpendicular to the direction of magnetic field.
Reason- The deflecting torque acting on a loop of magnetic moment m in a magnetic field B is given by the dot product of m and B.

Two long parallel wires kept 2 m apart carry 3 A current each, in the same direction. The force per unit length on one wire due to the other is-

(A) 4.5 x 10^-7 Nm^-1 , attractive

(B) 4.5 x 10^-7 Nm^-1 , repulsive

(C) 9 x 10^-7 Nm^-1 , repulsive

(D) 9 x 10^-7 Nm^-1 , attractive