Question

A metal wire PQ of mass 10 g lies at rest on two horizontal metal rails separated by 4.90 cm (figure 34 - E9). A vertically downward magnetic field of magnitude 0.800 T exists in the space. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below 20.0 $\Omega$, the wire PQ starts sliding on the rails. Find the coefficient of friction.

Answer 1

$\mu R=F$

$\Rightarrow \mu \times m\times g=ilB$

$\mu \times 0.10\times {10}^{-3}\times 9.8$

$=\frac{6}{20}\times 4.9\times {10}^{-2}\times 0.8$

$\mu =\frac{6\times 4.9\times {10}^{-2}\times 0.8}{20\times 0.10\times {10}^{-3}\times 9.8}$

$\mu =0.12$