Question

A horizontal wire of length $0.05m$ carries a current of $5A$. If the mass of the wire is $10mg$, the minimum magnetic field required to support the weight of the wire is : $(g=10m/s^2)$

• A. $4\times {10}^{-4}T$
• B. $25\times {10}^{-4}T$
• C. $4\times {10}^{-1}T$
• D. $25\times {10}^{-1}T$

Answer 1

The correct option is C $4\times {10}^{-1}T$

Magnetic force balances the weight of the wire,
$Bil=mg$
$B\times 5\times 0.05=10\times {10}^{-3}\times 10$
$B=4\times {10}^{-1}T$