Question

A straight wire of mass $300 \,g$ and length $ 2.5\,m $ carries a current of $ 3.5\,A $ . It is suspended in mid-air by a uniform horizontal magnetic field $B$. What is the magnitude of the magnetic field?

• A. $ 0.654\,T $
• B. $ 0.336\,T $
• C. $ 1.576\,T $
• D. $ 0.939\,T $

Answer 1

Answer: (B)

Here weight of the wire is balanced by the extene magnetic force.
So, $ Bil=mg $
$ B=\frac{mg}{il} $
$ =\frac{300\times {{10}^{-3}}\times 10}{35\times 2.5}=0.34\,T $