Investigating the Effect of Resistance on a Capacitor Circuit

Investigating the Effect of Resistance on a Capacitor Circuit

Method: We will set up the following circuit. We will measure the

capacitor pd. (Vc) with the cell connected.

Then we will remove the cell and connect point A to point B, at the

same moment starting a stopwatch. We will record the length of time

(t) for the Vc to decay to 3.75 Volts. We intend to repeat this

procedure using different resistors.

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Resistance (kW)

Time (s)

33

33

68

72

100

97

150

153

330

320

680

584

Conclusion:

From the graph we can clearly see that the time taken for the

capacitor to discharge is directly proportional to the resistance.

This is because the graph shows a definite straight line going through

or near most of the points. This means that the higher resistor you

use the longer it will take for the capacitor to discharge. The

experiment has therefore proved the prediction correct i.e. the

resistance should be directly proportionate to the time taken for the

capacitor to de-charge. This can be explained by the following:

Capacitors store electrical charge. When current is passing through

the circuit the capacitor charges up as the current can't jump between

the gap of the two plates but charge is held there because of the

force of the opposite poles. This means that more and more electricity

is stored until it reaches its full capacity. But when the circuit is

broken the capacitor de-charges releasing electricity through the

circuit. The resistor slows down the current causing 'congestion' and

means that the capacitor has to de-charge slower because only a

limited amount of charge can travel through a circuit with a high

resistance at any one given time.

Evaluation:

The method was a good way of carrying out the experiment as it was

quite easy to conduct once the circuit was connected, the results seem