Resistance would be affected for the same reason for the length of wire. There will be more electrons present in the thicker wires.
Temperature could affect the resistance because if the temperature of the wire increases then the atoms will have an increase of energy. This would cause more collisions between the electrons. The increase in collision would mean an increase in resistance. Therefore, if the temperature increases so does the resistance.
The material could affect the resistance because different materials will have different numbers of free electrons. The number of electrons depends on the number of electrons in the outer shell of the atoms. Therefore, there can be more or less electrons in the outer shell of different atoms, resulting in a change of resistance depending on the quantity of electrons.
For this investigation I am going to select the length of wire to determine if it changes the resistance.
Prediction
I predict that as the length of wire increases then the resistance will also increase. This is because the longer the wire the more atoms and therefore there is more electrons that are likely to collide with the atoms.
I also predict that if the length of the wire is doubled the resistance will double as well. This is because there will be double the amount of collisions, and twice as much energy is required, which will slow the flow of electrons down resulting in an increase in resistance.
Method
Apparatus required for this experiment:
- Different lengths of wire
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Battery – the power source
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Voltmeter - measures the voltage across the wire
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Ammeter - measures the current flowing through
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Variable resistor - as the resistor is varied it alters the current flowing through the circuit.
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Wires – connect the circuit together.
Apparatus
The apparatus will be set up as shown. Different lengths of wire will be introduced into the circuit, to determine whether the length of wire affects the resistance. The current and voltage will be measures and then the resistance will be calculated, and compared to the length of the wire.
Representing my results
I am going to obtain at least 5 different results in the range of 100cm to 500cm. I will repeat the results twice and calculate an average. The table below shows how I am going to represent my results.
Making this experiment accurate
Calculating an average will make the results more accurate because it will increase the reliability of the resistance. I will also use the same apparatus.
A variable resistor will be used. The resistance can be changed by sliding a slider. This will be used to alter the current flowing through the circuit. This is very useful because it allows the pointer to be on a scale division, therefore increases the accuracy.
If the voltage is not on a scale the division then I can interpolate, which is to estimate a value of between two known values.
Making this experiment a fair test
For this experiment to be a fair test:
- The same apparatus will be used
- The wire will be the same thickness
- The same material will be used, nichrome wire.
Preliminary experiment
A preliminary experiment was done to help decide the range of current to use for each different length of wire.
This was done by finding out the lowest possible current and the highest. This was done by using the lowest and highest power supply, and moving the slider on the variable resistor, to calculate the range.
The results were:
1 cell 0.02A (lowest power and current)
3 cells 0.27 (highest power and current)
Therefore the range of current for each length of wire was inbetween these two values.
In helping to prepare my planning I have referred to the following sources:
- Co-ordinated Science Physics Textbook
- CGP, GCSE Double Science, Physics revision guide.
GCSE Physics coursework
Investigate the factors affecting resistance of a piece a wire
Observing
Apparatus
Method
Different lengths of wire will we taken and added to a circuit. The resistance will be calculated, by finding out the voltage and current. A voltmeter will be used to measure the voltage and an ammeter to measure the current. A variable resistor will introduced to alter the current, which will make the results more accurate. The results will then be recorded in a table and graph, and any patterns that emerge will be recorded.
Results
How I could improve my results
There are several ways that could improve the results that I have obtained:
- Be more careful in reading off the values from the ammeter and voltmeter. The resistance could have been calculated wrong, due to human error.
- The experiment was done on a bench, and it is very easy to accidentally move the wires without knowing, and this can affect the readings, and therefore lead to the resistance being inaccurate. To improve this I could try my best to try and not interfere with the apparatus, and make sure that I am aware this could happen, so that I am more careful.
I have also represented my results in the form of a graph. I have marked a line of best fit, to make the results more general and smoother. The graph shows that as the length increases so does the resistance, which is shown by the line getting steeper.
This experiment proves my prediction to be correct because the as the length increases so does the resistance. My prediction is also correct because at 200m had double the resistance at 100m, so this proves that there are double the number of collisions between the atoms and the electrons.
100m 10.27 (approx 10 ohms)
200m 19.11 (approx 20 ohms)
This proves that as the length of the wire increases there are less free electrons to flow through the circuit because there are more collisions due to the electrons having further to travel.
Evaluating the evidence
I think that this experiment worked well, and my results were reliable. This is because most of the results lied close the line of best fit, so the evidence is reliable. The length of wire affects the resistance of the wire because the number of atoms in the wire increases or decrease as the length of wire increases or decreases in proportion.
This investigation has worked well, and has fitted my prediction.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material. If there is a greater number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms, when the length is increased the number of atoms will also increase.
I think my method was a good way of carrying out this investigation. This is because I had a sufficient power supply, and was able to make my results more accurate by using a variable resistor.
If this experiment was repeated I could make sure that the wires were measured accurately using a meter rule, and I could check it again to make sure they are the correct length.
If I were to extend this investigation I would investigate the resistance of wire at different lengths, and have values inbetween the range I have already investigated. I would also investigate other factors which affect resistance, such as thickness of wire, temperature, material etc. I could therefore draw a conclusion what materials have more resistance than others, and I could also find out the best conditions in which resistance can be minimised.
