A wire PQ of mass 10g is at rest on two parallel metal rails.The separation betweem the rails is 4.9 cm.A magnetic field if 0.80 T is applied perpendicular to the plane of the rails, directed downwads. The resisitance of the circuit is slowly decreased. When the resistance to bleow 10 `Omega` the wire PQ begins to slide on the rails .Calculate the coefficient of friction between the wire and the rails

Explanation

Wire PQ begins to slide when magnetic force is just equal to the force of friction, i.e.,
`mu mg=ilBsintheta(theta=90^(@))` Here, `i=E/R=6/20=0.3A`
`mu=(ilB)/(mg)=((0.3)(4.9xx10^(-2))(0.8))/((10xx10^(-3))(9.8))=0.12`