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# To investigate the capacitance and uncertainty of a capacitor.

Extracts from this document...

Introduction

Fawwaaz Hosein

Name: Fawwaaz Hosein

Group Members: Solmoi Park and Eric Mui

Experiment 3: Capacitor

Date: 5th March 2010

Aim: To investigate the capacitance and uncertainty of a capacitor.

Equipment:

• Multi-meter
• Analogue ammeter
• Resistor
• Capacitor
• Battery
• Switch
• Connecting wires
• Stopwatch

Method:

• The circuits are set up as shown in figures 3.1 and 3.2 respectively below.
• For the circuit shown in figure 3.1, the behaviour on the ammeter when the switch S is closed is described and accounted for. Ensure that a minute or two is allowed to observe the change.
• The second circuit shown in figure 3.2 is then set up and the behaviour on the ammeter when its position is moved is described and account for.
• The switch is then closed and the steady current I0 is recorded
• The switch is then opened and the time for the current (I) to reach particular values is recorded.
• The experiment is repeated two more times so as to acquire three sets of time (T1, T2, T3) for the current (I) in question and the average time (t) was also recorded.
• Using the average time a graph of lnI against t is plotted using the following equation:  Where y= lnI, x= t, gradient = and lastly y- intercept = lnImax

• Resistance(R) of uncertainty ±2% is measured using the multi-meter and the Capacitance (C) is found by using the gradient =  Middle

28

1

3.6

-10.48

26

1

3.8

-10.56

24

1

4.2

-10.64

22

1

4.5

-10.72

20

1

5.0

-10.82

18

1

5.6

-10.93

16

1

6.3

-11.04

14

1

7.1

-11.18

 T1 (s) T2 (s) T3 (s)

Conclusion

From the graph the correlation (R2) between lnI and time was very strong as R2 was found to be 0.99965. As the gradient is negative so to is the correlation, ergo as ln I decreases, Time (t) will increase.

Conclusion:

We measured the capacitance of the capacitor and its uncertainty to be: C = (1.23 ± 0.02) mF.

To reduce the uncertainties a digital multi-meter should be used together with data-logging equipment for measuring time to lessen the effect of reaction time when using a stopwatch, ergo increasing the all-round accuracy of the readings.

Using a varying resistors or resistors connected in series in place of the one in question would help in showing a change in resistance, changes the time. Ergo would be observed to remain constant in face of these changes.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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