A coil of 150 turns, each of area 0.003 m², carries 1.2 A in a field of 0.2 T…

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Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A coil of $150$ turns, each of area $0.003\ \text{m}^2$ , carries $1.2\ \text{A}$ in a field of $0.2\ \text{T}$ . Its turning effect is $\tau = NBIA\cos\alpha$ , where $\alpha$ is the angle between the plane of the coil and the field. Find $\tau$ when the coil lies along the field ( $\alpha = 0^\circ$ ), when $\alpha = 60^\circ$ , and when $\alpha = 90^\circ$ .

Need a reminder? The key ideaShow

In a motor, the two sides of a coil feel opposite forces, so the coil turns. The split ring (commutator) reverses the current every half turn, so it keeps turning one way. The largest turning effect is $\tau = NBIA$ ; at an angle $\alpha$ between the coil's plane and the field it is $NBIA\cos\alpha$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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