Question

Two thin long parallel wires separated by a distance b are carrying a current i amp each. The magnitude of the force per unit length exerted by one wire on the other is

• A. $\frac { \mu _ { 0 } i ^ { 2 } } { b ^ { 2 } }$
• B. $\frac { \mu _ { 0 } i ^ { 2 } } { 2 \pi b }$
• C. $\frac { \mu _ { 0 } i } { 2 \pi b }$
• D. $\frac { \mu _ { 0 } i } { 2 \pi b ^ { 2 } }$

Answer 1

Answer: (B)

$\frac { \mu _ { 0 } i ^ { 2 } } { 2 \pi b }$

Answer 2

Force per unit length

$= \frac { \mu _ { 0 } } { 4 \pi } \cdot \frac { 2 i _ { 1 } i _ { 2 } } { r } = \frac { \mu _ { 0 } } { 2 \pi } \cdot \frac { i ^ { 2 } } { b }$