- The surrounding room temperature should be kept constant, as an increase in temperature will cause the particles to move faster. This will affect the resistance.
- The same type of wire must be used each time to ensure that the cross sectional area and material as different materials have different conductivity.
- The current passed through the wire must also be kept the same, as a change will make the results hard to interpret.
Apparatus:
- Wire over 50cms in length
- 2 batteries
- 6 connecting wires
- 1 crocodile clip
- Voltmeter
- Ammeter
- Rheostat
Method:
- Connect circuit
- Adjust Rheostat until the ammeter reads
- Record voltage on voltmeter
- Repeat these steps for the following lengths of the wire constant, with the crocodile clip at:
- 5cm vi. 30cm
- 10cm vii. 35cm
- 15cm viii. 40cm
- 20cm ix. 45cm
- 25cm x. 50cm
- Using Ohm’s law, calculate the resistance of the wire
Safety:
This isn’t a dangerous experiment, but care must be taken when using electricity, by handling the equipment with dry hands.
Accuracy:
To ensure that the results I obtain are as accurate as possible, I will ensure that the following steps are taken, firstly making sure that each time the length of wire is measured it is measure to within the crocodile clips. I will also avoid using wire that is damaged and has kinks in it, as this could cause the resistance reading to be inaccurate. Lastly I will attempt to record the ammeter and voltmeter readings as soon as possible after the circuit has been set up, as a delay will cause the wire to heat up and give an imprecise reading. I intend to have to recordings for the voltmeter and ammeter, for each length of wire, with the use of the variable resistor. This will enable me to take an average, which will guarantee that are resistance results are as correct as they possibly can.
Results:
I took the average reading I obtained for the voltmeter and ammeter to calculate the resistance. This is shown in the table above.
I used the following formula to calculate the resistance:
RESISTANCE = VOLTAGE/CURRENT
R=V/I
Conclusion:
My table of results shows that as the length of wire increased, so did the resistance. This proves my predicted to be correct, as I also predicted that the rate at which the resistance of the wire increases would be directly proportional to the length that is increased each time. I conclude that this was true because the electrons in the current made more collisions as the length of the wire were increased; this caused the resistance to do the same.
Evaluation:
I felt that overall the results I obtained were accurate, and a true representation of the resistance of a wire at different lengths. I don’t think that if I was to redo the experiment, that increasing the amount of readings I investigated would give make my findings any more accurate. I could however test different types of wires, to investigate which materials have the greatest resistance. Another possibility would be not to use a wire at all, as a rheostat does basically the same job, though is less complicated and has less room for error and inaccuracy.