Question

Two long straight wires $P$ and $Q$ carrying equal current $10\, A$ each were kept parallel to each other at $5 \, cm$ distance Magnitude of magnetic force experienced by $10 \, cm$ length of wire $P$ is $F_1$ If distance between wires is halved and currents on them are doubled, force $F_2$ on $10 \, cm$ length of wire $P$ will be:

• A. $10 F _1$
• B. $8 F _1$
• C. $\frac{F_1}{8}$
• D. $\frac{F_1}{10}$

Answer 1

Answer: (B)

$8 F _1$

Answer 2

Force per unit length between two parallel straight
wires =2πdμ0​i1​i2​​

F2​F1​​=2π(25cm​)μ0​(20)2​2π(5cm)μ0​(10)2​​=81​

⇒F2​=8F1​