Passage IV

In 2 studies, students recorded the temperature changes that occurred in different liquids when the liquids were heated for 10 min each by various metal coils through which selected amounts of electrical current, I, flowed.

For each trial in the studies, the students carried out the following procedure: First, they poured 400 mL of a liquid into an insulated container fitted with a thermometer and a metal coil and sealed the container (see diagram).

With the liquid, the container, and the coil at room temperature, 25°C, the students began to stir the liquid with a magnetic stirrer. Next, they adjusted the voltage across the ends of the coil until I reached the desired value, in amps (A). For the next 10 min, they continued to stir the liquid. After 10 min of heating, they recorded T，the liquid's temperature, in °C, and computed △T, the difference between T and the liquid's initial temperature of 25°C.

Study 1

The students computed water's △T after 10 min of heating at each of several selected values of I, first with a copper coil, then with an aluminum coil, and finally with a tungsten coil. Plots of water's △T versus I for each metal coil are shown in Figure 1.

Study 2

With the aluminum coil, the students heated ethylene glycol for 10 min at each of the values of I selected in Study 1. For each value of I, they computed △T. They did likewise with vegetable oil, substituting it for the ethylene glycol. Plots of △T versus I for water (from Figure 1), the ethylene glycol, and the vegetable oil are shown in Figure 2.