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

A, B

Explanation

`F=f_(L)`
`N=mg`
`BiL=mu mg`
`mu=(BIL)/(mg)=(0.8xx6/20xx4.9xx10^(-2))/(10xx10^(-3)xx9.8)=0.12`