Question

Two long straight parallel wires P and Q carrying currents of 10 A and 20 A respectively in the same direction are placed in air with a separation of 10 cm between them. Another long straight wire R carrying a current of 5 A in the opposite direction is placed between the wires P and Q and parallel to them at a distance of 5 cm from wire Q. Then the magnitude of the net force acting on wire R per unit length is

• A. $6\times10^{-4}Nm^{-1}$
• B. $2\times10^{-4}Nm^{-1}$
• C. $4\times10^{-4}Nm^{-1}$
• D. $8\times10^{-4}Nm^{-1}$ \bigskip

Hint:

Always determine the direction of magnetic forces first. Many mistakes occur by adding magnitudes before checking whether the forces are attractive or repulsive.

Answer 1

The Correct Option is C