EXPERIMENT 167. To study the inductive action of one core upon the other.
412. Directions. (A) Arrange as for [Exp. 164], but join the wire from Zn of the cell to M ([Fig. 132]). In this way coil B will be cut out of the circuit. Place the coils in the E and W line.
(B) Find about how far the residual magnetism of the core of B can act upon the compass-needle, holding the compass on the side away from coil A, no current passing.
(C) Press the key for an instant, and note whether the magnetism of coil B has been made stronger or weaker. Explain the action of core A on core B.
EXPERIMENT 168. Magnetic figures.
413. Directions. (A) Arrange as in [Exp. 164]. With books, etc., fix a piece of smooth, stiff paper, or a sheet of glass, just above the poles of the electromagnets.
(B) Sprinkle iron filings upon the glass, and gently tap it while the circuit is closed at the key for a few seconds. Make a sketch of the magnetic figure produced. Do the lines of force from the opposite poles attract or repel each other? See [§ 417] for making permanent figures. (See "Things a Boy Should Know About Electricity" for drawings of magnetic figures.)
Note.—If possible, use two or three good cells in series for making magnetic figures, as a fairly strong field is best.
EXPERIMENT 169. Magnetic figures.
414. Directions. (A) Arrange apparatus as for [Exp. 165], and make the magnetic figure for this combination, as directed in [Exp. 168]. Sketch and study the results.