Question

A long straight wire carrying current of 30 A rests on a table. Another wire AB of length 1 m, mass 3 g carries the same current but in the opposite direction, the wire AB is free to slide up and down, The height upto which AB will rise is

• A. 0.6 cm
• B. 0.7 cm
• C. 0.4 cm
• D. 0.5 cm

Answer 1

The correct option is A 0.6 cm

Here,

$I_1=I_2=30A,m=3g=3\times {10}^{-3}kg,l=1m$

In equilibrium position,
$mg=\frac{{\mu }_{0}2I_1{I}_{2}l}{4\pi h};$ h = $\frac{{\mu }_{0}2I_1{I}_{2}l}{4\pi mg}$

$h=\frac{{10}^{-7}\times 2\times 30\times 30\times 1}{3\times {10}^{-3}}=0.6$cm