The following factors influence the resistance of a wire:
Thickness of the wire – the wire is similar to a corridor in a busy place and the electrons flowing through the wire are similar to the people going through the corridor. If the corridor was narrow the people would find it harder to get from one end of the corridor to the other, however if the corridor was wide the people would have more space and therefore find it easier to go through the corridor. The electrons move through the wire at the same speed regardless of the thickness, it is the amount of electrons that go through. A thicker wire has less resistance, so a higher rate of flow, where as a thinner wire has more resistance, so a slower rate of flow. if you double the cross sectional area of a wire you will cut its resistance in half.
Length – The length of a wire can also affect the resistance because it determines how much the electrons have to travel. If a wire is long, it would take the electrons longer to get from one end to the other than if it was a shorter wire. So if you double the length of a wire, you will double the resistance of the wire.
Temperature – The temperature of the wire does not have the same difference on the resistance than its length or thickness. A cold wire would have less resistance that a hot wire, this is because if the electrons inside the wire are hot and therefore have more energy the flow of the electrons would not run as smoothly than if the electrons were cold.
Material of the wire – Although in this experiment all of the wires that will be tested are of the same material (nichrome), the material of a wire also determines how much resistance a wire puts up. For example, copper is a better conductor of electricity than iron so it will have less resistance. But in this experiment all of the wires used will be the same material, nichrome.
Nichrome is an alloy of two metals, nickel and chromium.
In conclusion, a short, thick, cold wire would make a better conductor and would have a smaller resistance compared to a long, thin, hot wire which would have more resistance. However in this investigation, I will be investigating how length affects the resistance of a wire. The variable will be the length; however the thickness of the wire will remain the same.
Prediction
I predict that in this investigation, the wire which is thick or shorter in length will have a smaller resistance than a wire that is thin or long. The diagram shows how if the variable was to investigate the thickness of the wire there would be a greater surface area across the cross-section of the nichrome wire, which means that there would be a greater flow of electrons and the wire would not heat up as quick, however the variable that I will be using is the length so I predict that the longer the wire, the smaller the resistance, and the shorter the wire the greater the resistance. The reason a longer wire has more resistance than a shorter wire is due to the increased number of collisions along the length of the wire, the electrons lost electrical potential energy as heat, with the collisions.
Diagram
This picture shows the circuit we used in our experiment
The purpose of this experiment is to find out what factors influence the resistance in wires.
On this circuit we will test out different wires and measure the flow of electrons through each wire.
This circuit contains the following pieces of apparatus
- Power Pack/Cells
- Ammeter
- Voltmeter
- Metre rule with nichrome wire
- Wires
- Crocodile clips
Safety
In this experiment there a few safety precautions you must take. Such as making sure that your hands are not wet, hair is tied back and that if the wires In order to carry out a successful investigation safety precautions must be taken. This includes the following:
- Hands are not wet. This will avoid electrocution.
- Long hair is tied back. This will prevent vision from being interfered (one can see what she is doing).
- Bags are safely under the desk or at the front of the room to avoid one from falling over.
- If the wire starts to heat up too much, the power pack or battery must be disconnected immediately.
Fair testing
Independent and dependant variables
In this experiment the dependent variable is the length of the wire, the independent variable will be the material of the wire - nichrome and the thickness.
To keep this experiment as fair as possible, it was made sure that the ammeters and voltmeters were checked for accuracy before the test began
Method
1) Collect apparatus:
- Power Pack/Cells
- Ammeter
- Voltmeter
- Metre rule with nichrome wire
- Wires
- Crocodile clips
2) Set up the experiment as shown in this circuit diagram.
3) Place the crocodile to the nichrome wire which is 0.1 m long.
4) Switch on the power pack.
5) Record what the ammeters and voltmeters read, this will be the first attempt at 0.1m.
6) Now take the crocodile clips off the wire that is 0.1m long and connect to the wire that is 0.2m long.
7) Repeat step 5 but with move the crocodile clip to 0.3m, 0.4m, 0.5m, 0.6m, 0.7m, 0.8.0.9m, 1m.
8) Record the results.
9) Repeat the experiment for each distance 2 more times.
10) To work out the resistance of the wires, ohms law must be used. This is
Voltage ÷ Current.
11) Put the ammeter readings, the voltmeter readings, and the resistance in a table.
12) Record the results in a graph.
Results table and Graph on next page
Conclusion
To conclude my prediction that “the wire which is thick or short will have less resistance than a wire that is thick or long” was right. Ohm's law of resistance says, the current flowing through the circuit is directly proportional to the voltage applied.
My prediction was correct, because as the electrons flow through the wire at a steady speed they must slow down when they come to a different piece of wire. When the electrons move flow through the wire they must squeeze together so they can flow successfully through the wire. If the wire is too narrow, the electrons would have a harder time getting through the wire and it would take longer, therefore there is more resistance. However if the wire was thicker the electrons would find it easier to flow and, it would take less time to get to the other end of the wire so there is less resistance.
