Apparatus. A coil of wire (No. 89), described in [§ 390]; current reverser, C R (No. 57); dry cell; connecting wires, etc.
390. Coils of wire for some of the following experiments should be wound upon wooden spools that have been turned down thin, so that the wire will be as near the central hole as possible. They should be wound with a winder. (See Apparatus Book, Chapter X.)
For convenience we shall call the starting end of the coil, that is, the end that comes from the wire that is near the center, the inside end, I E. The end of the last layer of the coil we shall call the outside end, O E. These letters should be noted in the diagrams. See Apparatus List for details of the special coils used in these experiments.
391. Directions. (A) Arrange as in [Fig. 122], so that the axis of the coil will lie in the E and W line. Place O C about 2 in. from the E end of the coil. Press one lever of C R so that the current will pass around the coil for an instant in a clockwise direction; that is, so that it will enter the coil at O E. Note the action of the needle. If the needle is not affected move it nearer the coil and press the lever again. Get clearly in mind the connections, the direction in which the N end of the needle is deflected, etc. Is the E end of the coil a N or a S pole?
(B) Reverse the current through the coil. What effect has it upon the polarity of the E end of the coil?
(C) Place O C at the west end of the coil and repeat (A) and (B).
(D) Place O C in various positions about the coil and note the action of the needle when the current passes. Does this coil act like a magnet, having poles, magnetic field, etc.?
