As the length of the wire progressively increases, the number of atoms in the wire also increases, therefore more collisions between the atoms of the material and the electrons in the current, which will produce more heat.
Prediction
I predict that the resistance of a nichrome wire will increase as the length of the nichrome wire increases. This is because as the length of the wire is increased the electrons have to pass more atoms so the current will be slowed down further. Therefore the resistance will increase.
My Plan
In order to make my investigation fair the voltage needs to be kept the same. I changed the length of wire. 10 different lengths of wire will be used. Length of wire will be measured in cm. The length of wire that I used ranged from 10cm to 100cm. The experiment will be repeated three times and then an average needs to be taken. The voltage is measured using a voltmeter. The current is measured using an ammeter.
Fair Test
To make this investigation a fair test the tests will need to be done 3 times and then get an average for further accurate results. All the variables will need to be constant except for the length of wire. The length of wires will need to be measured accurately.
Variables
The variables are all the things in the investigation that can be changed (therefore factors which can affect the results) i.e. length, thickness, type, and diameter of the wire.
The conclusion and evaluation can also change depending on the results and how well the investigation is done.
Independent Variable
Independent variable is one factor chosen to change. The independent variable for this investigation is the length of the wire. It is not a constant factor in this investigation as its relationship with the resistance in a circuit is being investigated.
Dependent Variable
Dependent variable is the subject being measured and depends on the independent variable. The dependant variable is the resistance, as it will vary within the different conditions in the circuit. The resistance is not going to be constant as the length of the nichrome wire and its effects on the resistance in the circuit is being invested.
Safety
To make this investigation safe I made sure it’s done safely and with great care to prevent any accidents from occurring. To ensure the experiments are done safely goggles should be worn to protect eyes. Long hair should be tied back so it doesn’t get in the way. The current should be switched on for only a short period of time (about 5 seconds) otherwise the wire would become hot and if this does happen then the wire should given time to cool. This will help prevent harmful burns.
Apparatus
- Power Pack
- Voltmeter
- Ammeter
- Heat Proof Mat
- Meter Stick
- Wires with crocodile clips
- Wire of 10cm – 100cm
Diagram
Method
1) Collect all equipment listed above and set up the apparatus as shown in the diagram.
2) Connect the nichrome wire to the circuit, starting with 10cm length of wire.
3) Set the voltage on the power pack to 4V and used DC as the type of electrical supply.
4) Keep everything constant except the length of wire.
5) Switch on the circuit for only a short time (Otherwise the wire would have got hot and resistance would increase, therefore making the test unfair)
6) Read the current using the ammeter.
7) Read the voltage using the voltmeter.
8) Record results in a table.
9) Worked out the resistance using Ohms law:
Resistance (Ω) = voltage across wire (V), current through the wire (I).
10) Repeat this method, now simply change the length of wire to 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm, and 100cm
Results
Conclusion
The voltage was about the same as length of wire increased. The current decrease as the length of wire increases, examples using my results are 10cm = 2.55(A) and for 100cm = 1.02(A). The voltage and current was constantly changing by small amounts. The current changed significantly as the length of wire decreased. The reason the resistance decreased as the length of the wire decreased is because when the wire was longer there were more atoms inside, so the electrons path through the wire is longer. When a shorter wire was used the electrons got through easily and quickly. So when we took the readings the current higher. The length of the wire wasn’t directly proportional to the resistance according to my results. The results I found agreed with my prediction. I predicted that the resistance would increase as the length of wire increased. The difference in the resistance from 10cm and 100cm wire was 3.46 (Ω). This also backed up my prediction.
Evaluation
I think my results were as accurate as they could be, as the readings were rounded up to 2 dp. So the results weren’t 100% accurate.
I think that the experiment was generally a fair test but in some ways it wasn’t for example the length of the wire was not always exact maybe a couple of mm difference. Temperature is one of the key factors of resistance; for example in our experiment the temperature of the wire was high therefore the resistance become greater. It affects the resistance by making it higher as the electrons move faster at higher temperatures. I don’t think this experiment could be made any fairer as we did everything that we could to make this a fair test because the only way to make the experiment fairer was to be more accurate with the measuring of the wire. There are many different ways of extending our work to get more answers on the different affects on resistance. One way is by seeing how the thickness of a wire would affect the resistance. Or by experimenting with different materials and how they affect resistance.
