Question

Wires 1 and 2 carrying currents $\theta$ to each other. What is the force on a small element dl of wire 2 at a distance of r from 1 (as shown in figure) due to the magnetic field of wire 1

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Answer 2

Length of the component dl which is parallel to wire (1) is dl cos θ, so force on it

$F = \frac { \mu _ { 0 } } { 4 \pi } \cdot \frac { 2 i _ { 1 } i _ { 2 } } { r } ( d l \cos \theta ) = \frac { \mu _ { 0 } i _ { 1 } i _ { 2 } d l \cos \theta } { 2 \pi r }$.