EXPERIMENT 190. Rotary motion with an electromagnet and a permanent magnet.
454. Directions. (A) Arrange as in [Fig. 149]. Place the compass a short distance from the end of the core of the coil H (No. 89). Close the circuit, and as soon as the needle gets part way around open it again, closing it at the proper time to give the needle a new impulse. The speed can be regulated, somewhat, by changing its distance from the core. A key may be used in place of a reverser.
(B) Reverse the direction of rotation.
455. Discussion of Exps. 189–190. We have, in these experiments, the key to the action of electric motors. By properly opening and closing the circuit, the rotary motion can be kept up as long as current is supplied. If a small pulley were attached to the top of the compass-needle in [Exp. 190], a tiny belt could be attached, and we should have a machine that could do, perhaps, a fly-power of work. (See Electric Motors.)