A manufacturer of resistors uses a variety of wires to make resistors of fixed values. You are to carry out tests to investigate how he can produce resistors with different values of resistance.

Variables:

Variables which will affect the resistance of the wire are:

Length Thickness Material Resistivity Temperature

Variable to be investigated:

The variable which we are going to investigate will be the length.

Prediction:

I think that in the experiment, when we increase the length each time, the resistance will increase.

Planning experimental procedures

Independent Variable:

My independent variable will be the length.

Dependent Variable:

The quantity we will measure when we change the length will be the resistance.

Controlled Variable:

The quantities which I will keep the same will be the thickness, material, resistivity and temperature.

List of Apparatus:

Power Supply Unit

Rheostat

Ammeter

Voltmeter

length of wire which will be folded to 20, 40, 60 and 80cm

Block with crocodile clips for connecting wire into circuit

Diagram of Apparatus:

Method:

We set up the experiment as shown on the previous page. We connect the ammeter in serial in the circuit and the voltmeter in parallel. We put into the circuit two crocodile clips. When nothing is attached here, the circuit is incomplete but when we connect the different lengths of wire, the circuit is complete. For each length of wire, we will make 3 attempts; the first will be against a current of 0.2 amps, the second, 0.6 amps and the third - 1.0 amp.

To adjust the current each time, we turn the dial on the power unit and to attain the precise current, use the rheostat slider while observing the ammeter. We will then record the readings of the voltage each time. The reason we repeat the experiment three times, is to make sure that are recordings are accurate and to give us more results to record to reinforce our predictions.

After observing the experiment we tabulate the results to make them easier to examine. From these results, we will then construct a graph showing length against resistance. We will examine the graph and look fro any correlations or patterns that we could link to our conclusions.

Safety:

When increasing the current from the power supply, we must be careful not to increase it too far otherwise the wire may get very hot and snap (This is due to the melting point of the wire being exceeded) - this could result in burns if we are not careful. We must also remember to be wary of any leads and cables around us that we could pull with our hands and also not to operate the apparatus with wet hands due to the risk of electrocution.

Obtaining evidence

Results:

After the experiment has been carried out safely, we should tabulate are results. The results from the experiment are shown below:

Length of wire

(cm)

Current (A)

Voltage (V)

Resistance (ohms)

2

3

2

3

2

3

20

0.2

0.6

.0

0.11

0.34

0.55

0.55

0.57

0.55

40

0.2

0.6

.0

0.21

0.59

.00

.05

0.98

.00

60

0.2

0.6

.0

0.31

0.92

.43

.55

.53

.43

80

0.2

0.6

.0

0.42

.23

2.40

2.10

2.05

2.11

-

Interpreting and Evaluating

After carrying out the experiment and recording all the results into a table then turning them into a graph, we can see that the Independent variable investigated did have an effect on the resistance of the piece of wire.

From the results we can see that when we increase the current against the different lengths, the voltage increases each time. When we calculated the resistance (i.e. R=V/I) we could clearly see that the margin in the resistance fro each length of wire against the different voltages was within 0.8/0.9 of an ohm out each time and so they were very alike.

20

0.55

0.57

0.55

40

.05

0.98

.00

60

.55

.53

.43

80

2.10

2.05

2.11

From these results, we can draw the conclusion that:

The longer the wire, the more resistance it has.

Shown above in the results.

As we have drawn this conclusion from the results, I am confident that my results support my prediction.

I feel that the design of the experiment was reliable and the results that were produced from it are accurate. The only improvements I see that could be made to the experiment are 1. The measuring of the lengths of wire

2. The adjusting of the rheostat to attain the current.

Fortunately, the experiment produced good results meaning we had no anomalous results. I feel that it is for this reason, my results are strong enough to support my conclusion as already stated above.

GCSE Coursework