Question

A straight wire of length $50cm$ carrying a current of $2.5A$ is suspended in mid-air by a uniform magnetic field of $0.5T$ (as shown in figure). The mass of the wire is $(g=10m/s^2)$

• A. $100gm$
• B. $125gm$
• C. $62.5gm$
• D. $250gm$

Answer 1

The correct option is C $62.5gm$

Given : $B=0.5T$ $L=0.5m$ $I=2.5A$

As the wire is suspended in air, weight of the wire is balanced by the force acting on the wire in upward direction.

$\therefore$ $mg=BIL$

Or $m\times 10=0.5\times 2.5\times 0.5$

$⟹$ $m=0.0625kg=62.5$ $gm$