Question

A long wire AB is placed on a table. Another wire PQ of mass 1.0 g and length 50 cm is set to slide on two rails PS and QR. A current of 50A is passed through the wires. At what distance above AB, will the wire PQ be in equilibrium

• A. 25 mm
• B. 50 mm
• C. 75 mm
• D. 100 mm

Answer 1

The correct option is B 50 mm

Suppose in equilibrium wire PQ lies at a distance r above the wire AB
Hence in equilibrium $mg=Bil\Rightarrow mg=\frac{{\mu }_0}{4\pi }\left(\frac{2i}{r}\right)\times il\Rightarrow {10}^{-3}\times 10=\times {10}^{-7}\times \frac{2\times (50{)}^2}{r}=0.5\Rightarrow r=50mm$