This can be explained using the formula
R=V/I where R= resistance, V= Voltage and I= Current
The four main factors that affect resistance are:
- Temperature plays an important part as it can change the way the electrons move. By increasing the temperature the atoms start vibrating more rapidly and thus create an easy path for the electrons to move. If the temperature is decreased then the atoms stop vibrating rapidly and it becomes difficult for the electrons to bypass the atoms and so increases the resistance.
- The second factor is the material being used. The more free electrons the material has the less resistance it has such as copper and silver. But on the other hand if the material has no free electrons then it does not conduct electricity such as wood or plastics.
- The third factor which affects resistance is the length and thickness of the material. This is because when you have a long wire, the electrons have to squeeze together for longer to be able to pass through the wire than they do in order to be able to pass through a short wire. I predict that the longer the wire, the greater the resistance. If I had a 30cm wire and a 60cm wire, the 60cm wire would have a resistance twice that of the 30 cm wire.
- The final factor is the amount of power applied for the current to pass through, the more current is passed then there is more energy for the electrons to reach the positive terminal.
Current-voltage graphs show the relation between the current and the voltage passing through the material. The higher current the higher the voltage so there is a positive correlation between both of them. These graphs are useful for taking out different information from the graph such as a reading at a specific point.
The SI unit for resistance is the ohm (Ω).
Pilot study
The equipment used during this experiment is a power pack, variable resistor, wires, ammeter, voltmeter, crocodile clips, 1m of nichrome wire attached to a metre rule and a thermometer.
Method
- Collect apparatus: a voltmeter, an ammeter, wires, 2 crocodile clips and a power pack.
-
Set apparatus up as shown:
- Set the power pack on as low a voltage as possible. (So that there is not too high a current passing through the circuit.)
- Place the 10 cm of nichrome between the two crocodile clips to complete the circuit.
- Turn on the power pack and record what the ammeter and voltmeter read.
- Replace the 10 cm of wire with the 20 cm of nichrome remembering to keep the voltage the same. Turn on your power pack and record what the ammeter and voltmeter say.
- Change the wire to the 40 cm of nichrome wire and repeat the experiment.
- Work out the resistance for all the results using Ohm's law. V = I*R
- Record your results in a graph.
First of all we will connect the wires to the power pack. Then the ammeter will come in series to the negative end and then attach the voltmeter in parallel to the wires which will record the voltage. In the end comes the variable resistor from which we can keep the current constant.
After my pilot study I have realised that there are factors which will not make the experiment fair such as keeping the room temperature the same each time for the experiment and always letting the experiment cool down after being used. By doing these methods the experiment improves and is more accurate.
Results
My hypothesis was correct, the longer the wire the higher the resistance.
Ohm's law states that the current flowing through the circuit is directly proportional to the voltage applied. (If you double one, you double the other.)
I worked out the resistance of the wires by using the formula:
V/I = R or
This happens because of the electrons that flow through the wire. While moving through the wire, the electrons need to squeeze together. This is because there is not enough room/space for them to pass evenly through. The more the electrons have to bump together then the higher the resistance. This is because it will take longer for them to pass from one side of the wire to the other side. This is because the current is slowed down. (The longer the wire, the longer the electrons have to stay squashed together, and so the longer they take to pass through the wire and the higher the resistance.
The graph which compares the length of the wire to the resistance it gives travels in a straight line through the origin. This means that the size of the length is directly proportional to the resistance it gives. I can work out the gradient of this line by dividing the height of the line by the width. (Gradient = height/width)
The gradient of the graph for nichrome wire is: 1/16 = 0.0625
There were a few wayward results. This could have been because the wires were not exactly the correct length or because I did not read the voltmeter and ammeter accurately. The wires might have been over-heated The temperature of the wire will affect the resistance. Hotter wires will have a higher resistance than cold wires. To improve my results I should have obtained more than one result for each wire and length. I could have then worked out an average for more accurate results.
