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# Find out how the current through a filament lamp varies with the potential difference across it.

Extracts from this document...

Introduction

Investigation into the resistance of a filament lamp

Physics A 3883

Planning

Aim

For this investigation I have been asked to find out how the current through a filament lamp varies with the potential difference across it and hence determine how the resistance of the filament and the power supplied to it vary with the potential difference across it. I will also make estimates of the temperature of the filament for different potential differences.

Key factors

Independent variables:

• Current (Current will be measured with a digital ammeter/multi meter)
• Temperature (Thermometer to measure surrounding temperature)

Dependent variable

• Resistance
• Voltage (Will be measured with a digital voltmeter)

Controlled variable

• Filament lamp

The range of readings that I am going to take will be from 0 volts to 10 volts this is because it will give me a good set of data to work with.

I will increase the voltage by one volt each time.

To make sure I get good accurate fair results I will repeat the process at least 3 times.

When I do repeat the process I will make sure that I leave all the equipment as it is and not replace bits or add or remove components.

Middle

0.13

0.12

0.14

0.13

0.69

0.75

0.64

0.69

0.10

0.15

0.13

0.16

0.15

0.67

0.77

0.63

0.69

0.15

0.22

0.21

0.21

0.21

0.68

0.71

0.71

0.70

0.20

0.27

0.28

0.29

0.28

0.74

0.71

0.69

0.71

0.25

0.31

0.34

0.33

0.33

0.89

0.86

0.76

0.84

0.30

0.36

0.37

0.37

0.37

0.83

0.81

0.81

0.82

0.35

0.40

0.41

0.40

0.40

0.95

0.95

0.88

0.93

0.40

0.44

0.45

0.45

0.45

0.98

1.00

0.89

0.96

0.45

0.48

0.48

0.49

0.48

1.00

1.00

0.92

0.97

0.50

0.52

0.53

0.52

0.52

1.04

1.02

0.96

1.01

1.00

0.75

0.75

0.76

0.75

1.33

1.33

1.32

1.33

2.00

1.05

1.06

1.05

1.05

1.90

1.89

1.90

1.90

3.00

1.26

1.27

1.27

1.27

2.38

2.36

2.36

2.37

4.00

1.46

1.47

1.47

1.47

2.74

2.72

2.72

2.73

5.00

1.64

1.64

1.64

1.64

3.05

3.05

3.05

3.05

6.00

1.79

1.80

1.80

1.80

3.35

3.33

3.33

3.34

7.00

1.94

1.95

1.95

1.95

3.61

3.59

3.59

3.60

8.00

2.09

2.09

2.09

2.09

3.83

3.83

3.83

3.83

9.00

2.21

2.22

2.23

2.22

4.07

4.05

4.04

4.05

10.0

2.35

2.35

2.35

2.35

4.26

4.26

4.26

4.26

#### Results

Results table1

Resistance for filament lamp at 0°C=0.68Ω

Calculated From: Average resistance of (0.01v to 0.10v)/10

I didn’t use the data from 0.10 volts to 0.50 volts in any working because the heat was rising so was no good for calculating the resistance of

Conclusion

Also I would use the measured potential difference on the voltmeter as a variable rather that using it as a fixed variable because I could get even more accurate results.

Data

The main experiment went very smoothly, I got all the data that I wanted to but during the experiment where I was collecting the current for 0.01volts to 0.10 volts it was very had to collect accurate data because on the graph you can clearly see that there is a anomalous result (circled) this may have been human error or it could have been a random error like a power surge in the electric mains or a fault with the equipment. To overcome this in the future I would have a tolerance level for the current, e.g. if it wasn’t 0.20±2A then I would do it again, if it kept on happening then I would try changing some of the equipment, but then I would have to start all over again because of the differences in the equipment (if any). This would also give me a good indication if the original equipment was faulty, but the new equipment may and/or be faulty so I would have to make up my mind which to use.

2003

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