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A metal wire PQ of mass 10 g lies at rest on two horizontal metal rails separated by 5 cm as shown in fig. A vertically downward magnetic field of magnitude 0.80 T exists in the space. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below 20.0Ω, the wire PQ starts sliding on the rails. Find the coefficient of friction.
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For equilibrium, the magnetic force is equal to the friction force.
BIl=μmg where μ is the coefficient of friction and current I=V/R=6/20A
⇒μ=BIlmg=0.80×(6/20)×(5/100)(10/1000)(10)=0.12=3/25
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