Usually, a material's resistance increases with the rise in temperature as the voltage going across the wire has to avoid the resistor’s atoms more. This produces more energy causing plenty of heat.
The resistor is not the only thing that causes resistance in a circuit, all components in a circuit cause resistance. There are three variables that affect the resistance
- The Length of the wire.
- The Diameter of the wire.
- The Material the ‘resistor’ is made out of and the temperature of the wire.
The length of the wire affects the resistance because there will be more atoms for the current to pass through, hence the increase in resistance.
The diameter of the wire affects the resistance because the larger the diameter, the easier the current will be able to pass through because there will be more room within the wire.
The material the resistor is made out of will also make a difference. If the wire has a high density, there will be more atoms in the wire causing higher resistance, but if the wire has a low density, the atoms within the wire will be much lower, again providing less resistance.
The temperature will also make a difference to the resistance. If the temperature is high, there will me much more kinetic energy within the resistor and the atoms will be moving around. The current will find it difficult to pass through the wire hence there being an increase in resistance. When proceeding with the experiment, I am going to keep all the variables the same and alter just the length of the wire.
From the above table we can see that by doubling the length of the wire the resistance also doubles. The above table also shows that the voltage is the same as the resistance if the current is kept the same and if the length of the wire is proportional to the resistance and the voltage. The pattern you see above will change if the temperature of the resistor is altered in any slight way.
Prediction
I predict that by increasing the length of the wire, the resistance will increase. It is a fact that the larger the resistor – the more resistance. If any of the objects in a circuit are said to cause some resistance then I feel that the same will apply to the nichrome wire – the longer the wire, the more atoms the current has to pass through, causing an increase in resistance. I predict that the graph will also have a straightened out ending due to the heat being produced by the current in the wires. Temperature affects resistance so the higher the temperature of the wires the more resistance offered.
Apparatus
- 100 cm piece of nickel chromium wire.
- Ammeter
- Volt meter
- Power pack
- Wires
- Crocodile clips
- 1 meter rule
Method
Firstly, I set up the power pack with the wires leading out of it. I set the power pack at the standard 4 volts and was kept at the normal DC (direct current) supply. An ammeter and a resistor were added to the circuit with a volt meter being connected parallel to the resistor – thus allowing us to see the potential difference across the nichrome wire. Below is an image of what the finished circuit looked like.
I started the measurements at 20cm. The power pack was turned on and I read the readings from both the voltmeter and the ammeter. I turned the pack off and increased the length of the wire to 40cm. I repeated this process three times going up in increments of 20cms with the final measurement stopping at 100cm. I repeated the process three times in order for me to get an average, hence increasing the accuracy of my results.
I made this experiment a fair test by keeping both the voltage going through the circuit and the wire the same. Changing the wires in between experiments would have decreased the accuracy of my results greatly due to the diameter of the wire being slightly different. The material of the wire was kept the same. This would have made the experiment a fair test throughout and wouldn’t have give either of the tests an advantage or disadvantage.
Results
Analysis.
With scientific knowledge, the graph appears to have turned out like it should have with the results being accurate. As the length of the nichrome increases, the voltage increases but the current decreases. Using the following equation
Resistance = Voltage / Current I have worked out the resistance, according to Ohm’s Law.
By looking at my graph, I can see that the higher the voltage, the higher the resistance.
Evaluation
Overall, I feel that my results are fairly accurate. Human mistake is always possible and without comparing my results against somebody else’s results, I cannot be 100% sure that my results are accurate.
I believe I could have improved my results by increasing the accuracy in which I cut the nichrome wire. Even the odd one or two millimetres could have affected my results by a large margin.
The power pack may not have been turned off between altering the lengths of the wire – hence increasing the temperature of the wire. The increase in temperature at the start of the next measurement would increase the resistance ergo altering my results.
If I were able to make improvements to my experiment and repeat it a second time, I would be a lot more accurate in cutting the nichrome wire, however, none of my results are anomalous so I feel I have done a fairly accurate job in cutting them.
Due to the change in air temperature, I’m not 100% certain that the temperature was constant throughout the whole experiment. Another way I could have approached this experiment in order to make it even more accurate would be by submerging the circuit under water. The circuit would be the same but the resistor would be submerged under the water - the temperature could be monitored and kept to the same level throughout the whole experiment.
Despite these possible problems I feel that my results are fairly accurate and I have found out and shown that the resistance and the voltage are the same if the current is kept the same and that the resistance and the voltage are in proportion with the length of the wire.
