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Figure shows a circuit having a coil of resistance R = 2.5 Omega and inductance L connected to a conducting rod of radius 10 cm with its center at P. Assume that friction and gravity are absent and a constant uniform magnatic field of 5 T exists as shown in figure. At t = 0, the circuit is switched on and simultaneously a time-varying external torque is applied on the rod so that it rotates about P with a constant angular velocity 40 rad s^(-1). Find the magnitude of this torque (in mNm) when current reaches half of its maximum value. Neglect the self inductance of the loop formed by the circuit. |
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Answer» MAXIMUM current: `i_(0) = (B omegal^(2))/(2R)` Torque about the hinge `P` is `tau = underset(0) overset(l) int i(dx)Bx rArr tau = (1)/(2) iBl^(2)` Putting `i= i_(0)//2`, we GET: `tau = (B^(2)Omega l^(4))/(8R) = 5mNm` |
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