(B) Compare this resistance with that of Exp. 131.
=337. Directions.= (A) Measure the resistance of 1 meter of No. 28 German-silver wire. Use the wire as arranged on a board, Exp. 122 (Figs. 96 and 98), making the connections with the bridge from binding-posts, X and Z. (See Exp. 129, Note.) The wires connecting the bridge with the ends of the G-s wire will each have to be about 2 ft. long. In making deductions (§ 330) figure according to the length used.
(B) Divide the total resistance by 100 to get the resistance of 1 cm. of the wire, and carefully mark off the board into cm. This will give 100 parts between X and Z.
=338. Directions.= (A) Using the No. 28 G-s wire on the board, as arranged for Exp. 122, measure the resistance of the 2 meters in series, the connections being made with the bridge from X and Y, Fig. 98.
(B) Compare the result with that of Exp. 133. What is the relation between the length of a wire and its resistance? See Summary of Laws. (See Exp. 129, Note.)
=339. Directions.= (A) Measure the resistance of the above two meters of No. 28 G-s wire when joined in parallel. (§ 293.) The binding-posts, X and Y, can be joined by a short wire with connectors on its ends, or by clamping a thin strip across by means of spring connectors. Use the 2-ohm coil as the standard, and make proper allowances. (§ 330.)
(B) From the results of Exps. 132 and 135 what can be said about the resistances of parallel circuits as compared with the resistances of the separate branches?
=340. Directions.= (A) Arrange the 2 meters of No. 30 G-s wire on the table or board, again (Exp. 121, Fig. 96).
(B) Measure the resistance of one meter. Find the value of X approximately, and use a resistance for R that will suit. (See Exp. 129, Note.)
(C) Divide the result by 100 to get the resistance of 1 cm. of the wire.
(D) Compare the resistance of one meter of No. 28 G-s wire, found in Exp. 133, with the resistance of 1 meter of No. 30 G-s wire. What is the relation, then, between the size (area of cross-section) of a wire and its resistance? (See the results of Exp. 122, and § 319, also Summary of Laws.)
=341. Directions.= (A) Measure the resistance of 2 meters of No. 30 copper wire, arranged on a board as in Fig. 96. (See Exp. 129, Note.) Get the resistance of 1 meter.