First slide

Magnetic force

Question

A metal wire $P Q$ of mass $10 gm$ lies at rest on two horizontal metal rails separated by 5 cm. A vertically downward magnetic field of magnitude $0.800 T$ exists in the pace. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below $20 Ω$ , the wire $P Q$ starts sliding on the rails . Find the coefficient of friction.

Moderate

A

0.12
B

0.21
C

0.14
D

0.13

Solution

The wire starts sliding when magnetic force on the wire overcomes frictional force
$F = μ N \Rightarrow Bil= μ mg \Rightarrow μ = \frac{B \frac{E}{R} l}{m g} = \frac{0.8 \times 6 \times 0.05}{0.01 \times 10 \times 20} = 0.12$

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