Passage V

A capacitor is a device used to store electrical charge. Capacitance is the amount of charge a capacitor can hold at a given voltage.

A student used the circuit shown in Figure 1 to perform 3 experiments.

The parallel-plate capacitor consisted of 2 identical flat, parallel plates of copper, separated by a small distance(see Figure 2).

Initially, each plate of the capacitor was uncharged. (That is, each plate contained an equal number of positive charges and negative charges.) When the switch in the circuit was closed, electrons(negatively charged particles) flowed from Plate A of the capacitor through the ammeter, resistor, and battery to Plate B. After an amount of negative charge (Q)equaling -1 x 10^-8 coulomb flowed to Plate B, the switch was reopened, and the voltage(V)in volts, between the charged plates was measured.Finally, the capacitance(C)was calculated in farads(F).

Experiment 1

Two square copper 10-3 plates, each 0.05 m x 0.05 m (surface area 2.5 x 10^-3 m²), were separated by various thicknesses of air. The results are shown in Table 1.

Experiment 2

Three pairs of square copper plates, each pair having a different surface area, were tested. Each pair was separated by a 1×10^-4 m thickness of air.The results are shown in Table 2.

Experiments 3

The square copper plates from Experiment 1 were separated by a 1 x 10^-4 m thickness of various materials. The number K is related to each material's suitability for use in a capacitor. The results are shown in Table 3.