Laboratory manual in physics . ftermaking a half turn, but, on account of its inertia, itspoles move past the unlike poles of the horseshoemagnet. Then the coil is stopped and brought backby the magnetic force and the twisting force of theribbon by which the coil is suspended. If we coulddo away with the twisting force of the suspendingribbon could we produce a continual motion of rota-tion by reversing the current each half turn? Explain. Discussion.— The moving coil of an electric motoris mounted on a shaft so that continual motion ofrotation is possible. The current is brought into this 60
Laboratory manual in physics . ftermaking a half turn, but, on account of its inertia, itspoles move past the unlike poles of the horseshoemagnet. Then the coil is stopped and brought backby the magnetic force and the twisting force of theribbon by which the coil is suspended. If we coulddo away with the twisting force of the suspendingribbon could we produce a continual motion of rota-tion by reversing the current each half turn? Explain. Discussion.— The moving coil of an electric motoris mounted on a shaft so that continual motion ofrotation is possible. The current is brought into this 60 Laboratory Manual in Physics by means of an arrangement which changes thedirection of the current every half turn. Examinea toy motor and apply the principles learned in thisexperiment. EXPERIMENT No. 32 Question.— In electro-plating with copper, howlong will it take one ampere of current to deposit onegram of copper? Apparatus.— Copper plating bath with two lossplates and one gain plate; ammeter; rheostat; Directions.—Arrange the apparatus as shown in thediagram. {Caution.—Do not pass any current throughthe apparatus until the instructor has seen the con- Electricity and Magnetism 61 nections). The rheostat is a coil of resistance wire forregulating the amount of current and keeping itconstant. In electro-plating, the metal is alwaysdeposited on the negative pole. Pass the currentthrough the apparatus in such a direction that copperwill be deposited on the middle or gain the middle plate, rinse in w^ater, dry over agas flame, and weigh carefully to thousandths of agram. Return the coil to the solution, turn on thecurrent, and note the time and the reading of theammeter. Keep the reading of the ammeter con-stant by means of the rheostat. Let run for an evennumber of minutes, say 20; then remove the gainplate, rinse and dry it very carefully so as not toremove any of the copper, and again weigh. From data obtained calculate how long it would
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