Passage IV

Using the circuit shown in Figure 1, students studied the variables that affect the electrical resistance, R, of a wire.

The students used the following procedure to find R for each test wire. They immersed the test wire in an oil bath and allowed the test wire to come to the temperature of the oil. Keeping the test wire in the oil bath (to control the temperature of the test wire), they then closed the switch and, using the rheostat (a variable resistor), adjusted the electrical current through the test wire until the ammeter indicated 0.80 amp. As soon as the ammeter indicated 0.80 amp, they measured the voltage, V, across the test wire. Finally, they used V and the current (0.80 amp) to calculate R.

Study 1

The students found R for test wires made of different metals. Each wire was at the same temperature and was 100 cm long and 0.130 mm² in cross-sectional area (see Table 1).

Study 2

The students found R for copper test wires of different lengths. Each wire was at the temperature of the test wires in Study 1 and was 0.130 mm² in cross-sectional area (see Table 2).

Study 3

The students found R for copper test wires of different cross-sectional area. Each wire was at the temperature of the test wires in Study 1 and was 100 cm long (see Table 3).

Study 4

The students varied the temperature of the oil. At each temperature, they found R for the copper test wire used in Study 1 (see Table 4).