Practical to investigate the charging and discharging a capacitor

Apply Coulomb's Law to

(1) explain movement of charges.

(2) 2.2 Analyse the charging / discharging of a capacitor in a DC circuit.

In this investigation you are going to

(3) find out how resistance affects the rate at which a capacitor discharges.

You are provided with a capacitor C, a resistor R, a battery, a voltmeter, a two way switch, connecting wire and a stop watch.

Record the values of the capacitance and the resistance.

C = R =

Construct the circuit as shown in the diagram.

Adjust the switch to fully charge the capacitor. Measure the potential difference across the capacitor, V0.

Adjust the switch to allow the capacitor to discharge through the resistor and start the stop clock. Measure the potential difference across the capacitor every 20s until the capacitor has almost discharged. Record the readings in the table provided overleaf.

(4) Plot a graph of potential difference (V) against time (t).

Find the time taken for the potential difference to fall to 0.37 of its initial value. This is known as the time constant of the circuit ().

Repeat the experiment with a different resistor. Plot the graph of V against t on the same set of axes as the first graph. (AC 2.2)

Analysis and Discussion

Use information about the structure of a capacitor to explain why charge accumulates on the plates of the capacitor when the switch is in position 1. Use Coulomb's Law to explain the factors that limit the amount of charge that can be stored in this way. (AC 1.1)

Use the graphs to show that for a capacitor discharging through a resistor the time constant, = CR. Explain why the capacitor discharges much more slowly than it charges. (AC 2.2)

The criteria are Understand the principles of electrical conduction. 1.1. Apply Coulomb's Law to explain movement of charges.

2.2 Analyse the charging / discharging of a capacitor in a DC circuit.

Record the readings in the table:

	8.2 K W	180 k W
Time / S	Potential difference/V (1st experiment)	Potential difference/V (2nd experiment)
20	0.027	0.029
40	0.018	0.021
60	0.014	0.016
80	0.011	0.013
100	0.009	0.011
120	0.007	0.009
140	0.007	0.008
160	0.006	0.007
180	0.005	0.006
200		0.005

We start counting the reading from 045 V at seconds

can you please answer the question and give analysis and discussion