Apparatus. Galvanoscope, G V (No. 58); resistance coil, R C (No. 79); two-fluid cell, 2-F C ([§ 281]), or a dry cell; 6 connecting wires; metal plates, M P.
Arrange as in [Fig. 100], so that the current divides into two branches at M P 1. The branches unite at M P 2.
322. Directions. (A) Take the reading of G V with 2 ohms resistance in the lower branch; that is, with the whole of R C in circuit.
(B) Take the reading of G V with one ohm in circuit; that is, with the end of wire, 5, connected to M instead of to R.
(C) Cut out R C from the lower branch by replacing it with a metal plate, thus joining wires 3 and 5. Compare the results from (A), (B), and (C), and explain.
323. Current in Divided Circuits. Let us consider a circuit like that shown in [Fig. 101]. If the points, C and Z, were at the same potential, no current would pass from C to Z. As the current does pass, Z must be at a lower potential than C; there is a fall of potential from C to Z. If the branch, A B, has the same resistance as R X, the same amount of current will pass through each. [Exp. 124] has shown that when the branches have unequal resistances, most of the current passes through the one of small resistance. If R X has a greater resistance than A B, most of the current will pass through A B.
CHAPTER XIX.
MEASUREMENT OF RESISTANCE.
