EXPERIMENTS 158–163. To study straight electromagnets.
Apparatus. A good dry cell or other source of a fairly strong current; coil with soft iron core; key; wires with connectors, etc.; small nails; iron-filings; compass; large wire nail; tin box (No. 94) to act as a base for the electromagnets.
EXPERIMENT 158. Lifting power.
398. Directions. (A) Join the cell, key, and coil, as explained in [Exp. 154], so that the current will pass only when the key is pressed. Place the core inside of the coil([Fig. 125]). Two good cells in series can be used to advantage.
(B) Hold the coil in a vertical position near small nails, iron filings, tin boxes, etc.; then press the key and raise coil; carry the clinging iron to another place, break the circuit at the key, and explain the result. Why do nails cling more strongly to the core than filings after the circuit is broken?
EXPERIMENT 159. Residual magnetism of core.
399. Directions. (A) After the current has passed through the coil with the core in place, remove the core and test it for magnetism with the compass. Will the small end of the core attract both poles of the compass-needle, or is it slightly magnetized?
(B) If there is any residual magnetism, strike the core with a hammer and test again.
(C) Use a soft steel wire nail for the core, and repeat (A) and (B). Why does soft iron make a better core than steel for electromagnets? Which should be the more easily magnetized?