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)

$0.336\,T$

Answer 2

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