Question

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.

Answer 1

The wire starts sliding when magnetic force on the wire overcomes friction force.
`muN=F implies mumg=ilB`
`muxx.10xx10^-3xx10=6/20xx5xx10^-2xx0.8`
`mu=(6xx5xx10^-2xx0.8)/(20xx0.10xx10^-3xx10)=0.12`