Investigate the factors, which affect the resistance of constantan wire.

Temperature

For the temperature of the wire I would not be able to create a fair test because it is extremely difficult to produce and control the wide range of temperatures needed and record the results without the correct equipment. Therefore I will not be investigating this factor.

Wire Thickness

There is not a wide enough range of wire thickness available at school therefore I cannot choose this option, as with the power cells.

Length of Wire

To measure and record the findings for this factor would be practical and the equipment required is readily available. Therefore I will choose this factor to investigate.

New Aim

To investigate how increasing the length of constantan wire affects the resistance.

Prediction

I predict that if the length increases then the resistance will also increase in proportion to the length. I think this is because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. So if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance.

Extra Relevant Information

Co-ordinated Science

* A potential difference makes the free electrons move along

* All conductors have a resistance

* The thinner the wire the more resistance

* The thicker the wire the less resistance

* Ohms Law: The resistance of a wire does not change provided you do not change the conditions.

* Resistance = Voltage

Current

Definition (from Oxford Encyclopedia)

Resistance, is the ratio of the potential difference (p.d. or voltage) across a conductor to the electrical current, which flows through it as a result. The unit of measurement is the ohm (O), this being the resistance of a conductor requiring a potential difference of 1 volt across its ends to produce a current of 1 ampere. For a given metal conductor at constant temperature the value is the same whatever the current (Ohm's law), but rises if the temperature rises. Any conductor possessing resistance gives off heat when a current flows through it. Joule's law describes the effect.1

Starting the Investigation

Now I will start the investigation

Equipment Required

* Constantan Wire (300mm long)

* Ammeter

* Voltmeter

* Circuit Board (complete with necessary power cells, batteries)

* 2 Crocodile clips (to attach to the constantan wire)

* Normal copper insulated wire (to connect the ammeter and voltmeter to the power cells and constantan wire)

* Ruler (to measure the length of the wire, in mm to increase accuracy)

Plan

. Connect circuit as shown in the diagram

2. Record voltage on voltmeter

3. Repeat the experiment with the following lengths of wire, connected to the two crocodile clips

* 50mm

* 100mm

* 150mm

* 200mm

* 250mm

REPEAT THE EXPERIMENT 3 TIMES TO REDUCE ANY ANNOMILIES

Accuracy

To keep this experiment as accurate as possible I need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when I do this. I must also make sure that the wire is straight during the experiment. If it is not, short circuits may occur and bends and kinks in the wire may effect the resistance, also. The reading that I take of the voltage should be done fairly promptly after the circuit is connected. This is because as soon as a current is put through the wire it will get hotter and I want to test it when heat is effecting it the least, i.e at the beginning.

Blank Table of results

Length of wire

(CM)

Voltage (Volts)

Ampage (Current Amps)

Resistance

(Ohms)

5

0

5

20

25

Preliminary

Upon testing to see if the experiment would work I found no problems with the plan I described earlier. I was able to get the following results:

st Test

Length of Wire

(CM)

Voltage (Volts)

Ampage (Amps)

Resistance

(Ohms)

5

.35

.39

0.97

0

.88

.05

.79

5

2.25

0.81

2.77

20

2.46

0.68

3.6

25

2.61

0.58

4.5

2nd Test

Length of wire

(CM)

Voltage (Volts)

Ampage (Current Amps)

Resistance

(Ohms)

5

.28

.32

0.96

0

.79

.02

.75

5

2.16

0.81

2.6

20

2.12

0.68

3.1

25

2.57

0.58

4.43

3rd Test

Length of wire

(CM)

Voltage (Volts)

Ampage (Current Amps)

Resistance

(Ohms)

5

.21

.34

0.9

0

.79

.00

.74

5

.13

0.80

.4

20

2.43

0.65

3.7

25

2.50

0.53

4.7

Calculations made on separate paper.

These results seem to show a strong correlation I will now draw a scatter graph to show any anomalies. There seem to be three anomalous results this could be caused by:

* Not waiting long enough for the Voltmeter or ammeter to get an accurate reading

* Maybe too much or too little wire was used i.e 17.5 instead of 15

* Rushing the experiment.

I have recorded all three sets of results on one graph so that an easy comparison can be made between the results.

The graph proves my prediction to be correct as the resistance increases proportional to the length of wire. In my prediction I said that:

If the length increases then the resistance will also increase (ohms law: I have changed the conditions i.e added more wire) in proportion to the length. From my graph I have shown my prediction to be correct, as the line of best fit is a straight line proving that the resistance of the wire is proportional to the length. The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. The resistance of the wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire.

Evaluation

From my results table and graph I can see that my results that I collected are very relliable. I know this because most of my results (apart from the results collected on the 3rd test) follow a straight line, the line of best fit.

During my experiment I noticed several modifications I could make to improve on the investigation if I was to repeat it,

* Instead of connecting the voltmeter to the main circuit I would connect it to the wire which is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well.

* Use pointers instead of crocodile clips, I would do this because pointers would be more accurate as the tips have a smaller surface area than the crocodile clips giving a more accurate measurement of the wire.

As well as making these modifications I would also improve my investigation by testing different thicknesses of wire. I would do this to expand on my investigation.

Any errors in my experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight whilst holding it next to a ruler then trying to accurately attach two crocodile clips to the right part of the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection, this also meant that they were easy to move about on the wire changing the length of it making inaccurate results. Errors rarely occurred in the setting or the current and the reading of the voltage, it was just in the preparation that they did occur. Another example of this is the wire was never totally straight when we started the experiment, which may also, as said earlier on, effect the resistance of it.

I do not think that doing any more tests in my experiment would have made the results any more accurate. I feel that the only way to make it more accurate would be to use a different method- perhaps were we had a bar that did not bend in place of the wire. We could even use a rheostat in place of the wire, because it is essentially a long coiled wire that is connected at different lengths to change the resistance of the circuit.