Determining the Half-Life for the Discharge of a Capacitor-Resistor Circuit

Determining the half-life for the discharge of a Capacitor-Resistor Circuit

This experiment was set out to determine the half-life for the discharge of a capacitor resistor circuit. The results obtained for the discharge currents, enabled the determination of half-life for the circuit.

According to theory, half-life is defined as; t1/2 = 0.693 RC, where R = resistance value and C = capacitor value.

Apparatus

• 500 µ farad capacitor

• 100 kilo-ohm resistor

• Digital multi-meter (100 µ amps DC)

• DC power supply

• Stop clock

• Two way switch

• 7 lengths of wire

Diagram

Method

The apparatus was set up as shown in the previous diagram. The DC power supply was set to 5.0V and the flick switch set to mark X. This setting ensured the capacitor was connected directly to the power supply allowing it to charge, therefore disconnecting the resistor and multi-meter. Using the stop clock, the capacitor was left to charge for 40 seconds.

As soon as the stop clock measured 40 seconds, the flick switch was set to mark Y, disconnecting the capacitor from the power supply and connecting it across the resistor and ammeter. The stop was restarted and the current readings on the multi-meter were recorded every 10 seconds for a total of 180 seconds (3 minutes).

Results

Below is a collection of results showing that as the time increased, the discharge current of the circuit decreased. Showing the initial current was the highest value, from when the flick switch was set to Y.

Time/ seconds Current/ µ amps

0 48.1

10 39.3

20 33.2

30 28.1

40 23.8

50 20.0

60 17.2

70 14.3

80 12.0

90 10.2

100 8.8

110 7.3

120 6.2

130 5.2

140 4.4

150 3.7