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# To investigate the effect the length of a wire has on the resistance

Extracts from this document...

Introduction

Reshmal Barot

11/4

Aim: To investigate the effect the length of a wire has on the resistance

V = I x R

Voltage = Current x Resistance

What is electric current and how is it measured?

Electric current is defined as the rate of flow of electric charge. Electric current is measured as the amount of charge which flows past a particular point in a particular point. Current is measured in amperes, but when written can be shortened to ‘A’ or ‘amps’. Below is the equation used to measure current in amperes.

Current (amps)    =         charge passing in coulombs

Time interval in seconds

An ammeter is used to measure electric currents, the ammeter measures how much charge is passing through it. An ammeter should be connected in a series circuit; also the positive terminal of the ammeter should be connected to the wire coming from the positive power supply. However it does not matter where you put the ammeter in the circuit, as long as the circuit doesn’t branch anywhere.

In order to for current to flow in a circuit a potential difference must exist.

What is potential difference and how is it measured?

Potential difference is also known as the voltage. The potential difference between two points in a circuit is defined as the amount of electrical energy changed to other forms of energy when a coulomb of charge passes between those two points.

Middle

0.4

0.3

0.75

0.79

0.38

0.3

0.79

0.38

0.3

0.83

25

0.4

0.4

1

1.05

0.38

0.4

1.05

0.36

0.4

1.11

30

0.44

0.6

1.36

1.39

0.4

0.6

1.5

0.38

0.5

1.32

35

0.46

0.8

1.74

1.65

0.44

0.7

1.6

0.42

0.7

1.6

40

0.44

0.8

1.81

1.67

0.42

0.8

1.9

0.44

0.8

1.81

As well as being able to select the suitable equipment, this test showed difficullty in building a circuit. At first I found setting up a voltmeter/ ammeter and variable resistor into the circuit quite difficult, but whilst practicing in the preliminary test, I became fairly confident and built it accurately and promptly.

Method:

In my method I followed my plan, leaving it unchanged. (The plan can be found on page 4.) I repeated this process six times, to ensure accuracy of results and to solve any anomalous results. The measurement of the length of the wire was done in multiples of five, the resistance board included a 40cm wire, and therefore eight different lengths were experimented on, each going up by 5cm. After experimenting with the power supply on two volts, I trialed the test again, but this time setting the power supply on four volts.

Results

The table below shows my results whilst the power supply was set on two volts.

 Length (cm) Current    (amps) Voltage (volts) Resistance (ohms) Average total resistance (ohms)

Conclusion

If doing this test again I would like to develop a way to control the temperatures of the wires, giving me a better indication of the relationship. Also so that I have even greater accuracy I would use newer and more accurate ammeters and voltmeters over a wider range of lengths. I would also like to look into how the diameter affects the resistance.

It was important to have control over the factors that affect resistance; a key factor was the length of the wire; I controlled this by straightening out the wire before measuring to make sure there were not any kinks that would add to the length. One factor I felt I had lees control over was the potential difference applied, I was reliant on the power pack setting and in doing this investigation again I would look into setting greater control.

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