EXPERIMENT 178. To find whether a current can be generated with an electromagnet and a hollow coil of wire.
433. Directions. (A) The hollow coil (No. 90) should be joined to the astatic galvanoscope, as shown in [Fig. 136]. Instead of the bar magnet in [Fig. 136], an electromagnet is to be used, and this should be joined in series with a cell and key, as shown in [Fig. 138]. The current from the cell will pass only when K is pressed.
(B) Note from the winding which way the current must pass around the coil when the circuit is closed at K, and determine whether the lower end of the long iron core, L I C (No. 96) should be N or S. With the compass test the poles of the core to be sure you are right.
(C) Quickly lower the end of L I C into the hollow coil (H, [Fig. 136]), the circuit being kept closed long enough to allow the needle to partially come to rest again. Withdraw L I C before you open the circuit. Explain action of needle.
(D) Reverse the direction of the current through the electromagnet, by changing the connections, and repeat (C). Does any induced current pass through A G when the core is held still in the coil H, even though a current passes through coil E?
EXPERIMENT 179. To find whether a current can be generated with an electromagnet and a coil of wire having an iron core.