What Factors Affect the Resistance of a Piece of Wire.

What factors affect the

Resistance of a piece of wire.

Planning

I will investigate by experiment the factors that affect the resistance of a piece of wire. There are many factors so I have chosen to focus on length. We measure resistance in ohms Ω.

I will try to make a fair experiment by using the same equipment for all of my readings. This will give me better and clearer results. There are some factors, which are hard to control such as heat and condition of the wire.

Ohm’s law is:

“The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.”

Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. The collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire.

Method

I will take a piece of wire and attach it to a board in 50cm lengths, but it won’t be separate lengths it will be one long piece wrapped round the nails at either side of the board in a zig zag pattern. I then will attach crock clips to either side of a 50-cm piece of wire and pass electrical current into the wire and I will measure the current going into the wire and the current going out of the wire. I intend to take 10 readings covering a span of 500cm and I will take 4 readings at each 50cm interval in volts and amps to give certainty to it I will find an average of the 4 results and discard any that are unusual from the others.

Once all readings are taken I will work out the resistance of the wire by using this formula tri-angle:

V= VOLTS

I= CURRENT

R= RESISTANCE

Equipment

I will use this equipment to make my circuit in the way shown below:

1 ammeter

1 voltmeter

2 crocodile clips

1 variable resistor

1 long length of wire

Set-up

Prediction

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Once all readings are taken I will work out the resistance of the wire by using this formula tri-angle:

V= VOLTS

I= CURRENT

R= RESISTANCE

Equipment

I will use this equipment to make my circuit in the way shown below:

1 ammeter

1 voltmeter

2 crocodile clips

1 variable resistor

1 long length of wire

Set-up

Prediction

I predict that the smaller the pieces of wire the lower the resistance and vice versa. I think this prediction is true because I think a lot of currents flowing through a small piece of wire will produce too much heat and the wire will snap. Also the longer the piece of wire the more atoms there are to collide with the electrons. So if I doubled the piece of wire I would double the resistance.

The experiment

I will take four voltmeter and ammeter readings for each of these lengths and find an average for each length and from that average I will find the resistance.

50cm

100cm

150cm

200cm

250cm

300cm

350cm

400cm

450cm

500cm

Gathering results.

I did the experiment many times and most of my readings fell very close but one or two were odd so I didn’t use them in finding the average. As I did the experiment so many times I think this made my results fairly accurate. I used different power packs one day so I re did took the results with the same one but I found it made very little difference. I tried to make it as fair as an experiment as I could but areas, which I couldn’t control or found hard to, were:

Heat
Condition
Shape
Insulation of the wire
Thickness

I have made a list of results of the test:

I have noticed that the first reading for each length is the most unusual and different from the rest so I have not used all of the first readings for each length.

Graph of results

Conclusion

In my prediction I said that:
If the length increases than the resistance will also increase in proportion to the length of the wire.
From my graph I have shown that my prediction was correct, as the Line of Best Fit is almost a straight line proving that the resistance of the wire is proportional to the length of the wire.
The length of the wire affects the resistance of the wire because there are more atoms when the wire length increases and less, if it decreases.

The resistance of a wire depends on the number of collisions the electrons have with the atoms of the wire, so if there is a larger number of atoms there will be more collisions, which will increase the resistance of the wire.

Evaluation

I think this experiment went well. It was well controlled and I took many readings giving me accurate answers.

The things such as heat, insulation and condition I found hard to control as my readings were taken on different days. I thought that the change in power packs would make a difference to my readings, which it didn’t, so I could have saved time there by not re doing most of my readings.

From my results, table and graph I can see that the experiment I conducted was reliable. My table shows that the first lot of results for each measurement shows abnormality as they give far different readings from all of the others I took for each measurement. Also on the graph I see that there are no odd averages as it is almost straight.

If I were to do this experiment again I would use pointers instead of crock clips, as they are more accurate. This is because the tips have a smaller surface area and less energy would be lost if I used them. Otherwise my experiment was fair and produced very good results.

Sophie Johnson 11lk Physics coursework 02/05/07 04:16