Question

Two long parallel wires separated by a distance r have equal currents I flowing in each. Either wire experiences a magnetic force F N/m. If the distance r is increased to 3r and current in each wire is reduced to I/3, the force between them will now be –

• A. 3F N/m
• B. 9 F N/m
• C. (F/9) N/m
• D. (F/27) N/m

Answer 1

Answer: (D)

(F/27) N/m

Answer 2

F = $\frac { \mu _ { 0 } } { 2 \pi }$ $\frac { \mu _ { 0 } } { 2 \pi }$ =