A circular wire loop of radius R, mass m carrying current I lies on a rough surface (as shown in Fig. 1.86). There is a horizontal magnetic field `vec B.` How large can the current I be before one edge of the loop will lift off the surface?

Explanation

The loop will start to lift off when the magnetic torque equals the gravitational torque as shown in Fig.
The magnetic torque acting on the loop,
`tau_m=MB=IpiR^2B`.
The gravitational torque exerted on the loop, `tau_g=mgR`.
So, `IpiR^2B=mgR implies I=(mg)/(piRB)`
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