Question
In a dynamo, a coil of area 0.2 m^{2} and having 100 turns rotates in a magnetic field of 0.1 Wb m^{–2} with an angular velocity of 100 rad s^{–1}. The output terminals are connected through a resistance of . Calculate the torque , as a function of time t, required to keep the coil rotating.

4 sin 100t

4 cos 100t

3 sin 50t

None of these
diffcult
Solution
4 sin 100t
In usual notations, the maximum value of the emf induced in the coil is given by
.
The maximum current in the circuit is
The instantaneous current in given by
.
Let l be the length and b the breadth of the coil (assumed to be rectangular), carrying current i in magnetic field B. The forces experienced by each longer arm, N i B l, from a couple of moment . The torque experienced by the rotating coil is thus given by
.
An opposite torque of magnitude 4 sin 100t newtonmeter is required is keep the coil rotating with uniform angular speed.
SIMILAR QUESTIONS
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