Question

Two long and parallel straight wires A and B are carrying currents of 4 A and 7 A in the same direction are separated by a distance of 5 cm. The force acting on a 8 cm section of wire A is

• A. 3 × 10-6 N
• B. 6 × 10-6 N
• C. 9 × 10-6 N
• D. 12 × 10-6 N

Answer 1

Answer: (C)

9 × 10-6 N

Answer 2

Here, $\mathrm { I } _ { 1 } = 4 \mathrm {~A} , \mathrm { I } _ { 2 } = 7 \mathrm {~A}$

$\therefore \mathrm { F } = \frac { \mu _ { 0 } } { 4 \pi } \frac { 2 \mathrm { I } _ { 1 } \mathrm { I } _ { 2 } \mathrm { I } } { \mathrm { d } } = \frac { 10 ^ { - 7 } \times 2 \times 4 \times 7 } { 5 \times 10 ^ { - 2 } } \times 8 \times 10 ^ { - 2 }$

$= 89.6 \times 10 ^ { - 7 } \mathrm {~N} = 9 \times 10 ^ { - 6 } \mathrm {~N}$