Several questions now come up. Can a current of electricity in a conductor induce a current in another conductor not in any way connected with the first? Can current electricity produce effects through space? Is there an electromagnetic induction?
It has been seen that a current-carrying wire has a magnetic field, and that magnetic fields can act through space. It is evident, then, that a conductor will be surrounded and cut by lines of force when it is placed in a magnetic field, or near a wire or coil through which a current passes. Let us study this by experiments.
EXPERIMENTS 175–182. To study induced currents.
Apparatus. The two coils of wire (Nos. 89, 90); two short, soft iron cores (Nos. 92, 93); long iron core (No. 96); bar magnet (No. 97); astatic galvanoscope (No. 59); dry cell (No. 51); key (No. 55); horseshoe magnet; connecting wires with spring connectors (No. 54) on the ends ([§ 226]–[230]); coil of wire (No. 98) wound on an iron core; compass.
EXPERIMENT 175. To find whether a current can be generated with a bar magnet and a hollowed coil of wire.
427. Directions. (A) Arrange as in [Fig. 136]. The coil (No. 90) of fine wire is joined to A G (No. 59) as shown. Small pieces of tin or copper, 1 and 2, are used to make connections between the coil ends and wires, 3 and 4, which are attached to the galvanoscope. It is best to use the wires, 3 and 4, so that the coil will be 2 feet at least, from A G; otherwise the needle of A G might be affected by the magnet, M (No. 97).
(B) Get clearly in mind in which direction the right-hand end of the needle is deflected when a current enters A G at L, the left-hand binding-post. If you have forgotten the results of previous experiments, use the cell for an instant, touching the wire from the carbon to L and that from the zinc to R. If any currents come from the coil, later, you should be able to tell in which direction they flow, the coil and A G forming a closed circuit.
(C) Hold the magnet, M, as shown, and quickly push it into the coil until it has the place of a core, at the same time watching the needle. If a current is produced, in which direction does it flow from the coil? Does the needle remain deflected? Is the current constant or temporary?