331. Directions. (A) As explained in [Exp. 126], measure the resistance of the 10-turn coil of G V, allowing for connections ([§ 330]). Read the bridge-scale carefully.
(B) Use one-half of the 2-ohm coil as standard and repeat.
332. Directions. (A) Measure the resistance of the 5-turn coil of G V (see [Exp. 126], etc.), using 2 ohms as standard.
(B) Use 1 ohm as standard, repeat, and compare results.
(C) Add the resistances of the 5 and 10-turn coils, and compare the sum with the resistance of the 15-turn coil, as found in [Exp. 126], D. The difference should be but a few hundredths of an ohm.
333. Directions. (A) Measure the resistance of the coil of No. 24 copper wire (No. 89). This coil is used for later experiments. Spring connectors are fastened to the ends of this coil, allowing it to be directly connected to the conductor on the bridge, so no allowance should be made for its connecting wires. (See [Exp. 126] for details.) Mark the resistance upon the coil for future use. (See Note.)
Note. The student will be surprised, perhaps, to find that different results are obtained for the resistance of a given wire in case he uses different standard resistances in the various tests; that is, he will probably get a different result in [Exp. 127] (A) from the result of [Exp. 127] (B). The difference here, however, may not be large. The best results are obtained by making the standard resistance as nearly equal as possible to the resistance to be measured, so that a balance can be found when the end of wire 3 ([Fig. 105]) is near the center of the bridge-wire. If R, [Fig. 105], is much larger or smaller than X, the point desired on G-s W will be near one of its ends, and large errors thereby produced. The approximate resistance of X can be found by trial, then more or less resistance can be used for R to suit. The student should make several coils as explained in Apparatus Book, Chapter XVII. The resistance of the different coils furnished should be measured and marked. These can be used to vary the value of R.