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

A metal wire PQ of mass 10g lies at rest on two horizontal metal rails separated by 5cm as shown in Fig. A vertically downward magnetic field of magnitude 0.80T exist in the space. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below `20.0Omega` the wire PQ starts sliding on the rails. The coefficient of friction between wires and rails is found. The coefficient of friction between wires and rails is found to be `n//25`. find n