An Investigation into Factors Affecting Resistance of a Wire

Rob Stanyer LEE 10 A

Plan:

The possible variables I could use to find out factors affecting resistance are material wire is made of, length of wire, temperature and cross sectional area of wire. I will use cross sectional area of wire and length of wire because I think it will be hard to draw conclusions from the material of wire. I am not doing temperature because it would be hard to get results from and I think they wouldn’t be as accurate.

I will set up a circuit to find out how length and cross sectional area affect resistance.

I will need the following components in my circuit to gather all of the necessary results:

Component holder- So I can change the wire that I am testing.
Voltmeter- Measuring potential difference across the wire, it will have to be across the wire and not just anywhere in the circuit so it is measuring the P.D across the wire I am testing only.
Ammeter – measuring current of the circuit, with his and the voltmeter I will be able to work put resistance (R=V/I). As a safety consideration I will keep the Current under 0.5 amps, so the wire doesn’t get too hot.
Rheostat- So I can vary the voltage in the circuit to take two readings for each wire at different voltages, I will work out an average of the two to reduce the margin of error.
Switch- A safety consideration, so the wire doesn’t overheat and burn if the circuit is left on for too long.

I have decided to test length of wire at, 10cm, 30cm, 50cm, 70cm, 90cm, 110cm, 130cm, 150cm and 170cm keeping a constant cross sectional area of 0.028mm2. I will test cross sectional area at the Cross sectional areas of wire: 0.028 mm2, 0.045 mm2, 0.057 mm2, 0.113 mm2, 0.166 mm2 and 0.246 mm2, keeping a constant length of 50cm. My preliminary work reviled that these were the best constants, and variables to use as they gave a wide rang of results. For the length of wire I have decided to keep the wire at a constant width of 0.19MM, and for Cross sectional area a constant length of 50CM to ensure a fair test and to make my results accurate. For both the wire will be made of constantan, for the same reason.

Method: To gather my results I did the following procedure, using the circuit on the next page.

Place 10CM of, constantan wire with a cross sectional area of 0.028 mm2 in specimen holders.
Press switch to let current flow.
Record Potential difference of wire and current of the circuit
Work out resistance, (V/I)
Repeat for all chosen lengths
Once done repeat for cross sectional area, keeping the length at 50cm.
For both cross sectional area and length of wire I will repeat steps 1 to 5 twice to decrease the margin of error.