A matel wire PQ of mass 10g lies at rest on two horizontal metal rails separated by 4.90 cm . 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.

Explanation

`muR = F`
rArr` mu xx m xx g = iLB `
` mu xx 0.10 xx 10 ^(-3) xx 9.8 `
` = (6)/(20) xx 4.9 xx 10^(-2) xx 0.8 `
` mu = (6 xx 4.9 xx 10^(-2) xx 0.8) /(20 xx 0.10 xx 10^(-2) xx 9.8 ) `
` mu = 0.12 ` .