The structure of an atom
Variables:
Dependant- Resistance of the wire
Independent- Length of the wire
Control- Temperature, material of wire, Cross-sectional area of the wire
I need to keep the temperature constant because if it was to increase then the resistance would increase so I must keep the current low.
I need to keep the material of the wire the same because each metal has a different resistance so I must use the same type of wire each time- I am going to use Nichrome wire from the same reel to ensure this.
I need to keep the cross-sectional area of the wire the same because thick wire has less resistance than thin wire and for my experiment I will use SWG 32 Nichrome wire.
Predictions:
- (Qualitative) If the length of the wire is longer then the resistance will be bigger.
- (Quantitative) Doubling the length of the wire would double the resistance.
If resistance is directly proportional to the length of the wire then my graph that I would draw from my results would look like this:
Resistance/Ω
Length of wire/cm
A directly proportional graph is a straight line graph that goes through the origin.
If I double the length of the wire then I will be doubling the amount of resistance. This is because the free electrons are pushed around the circuit because there is an electric field in the nichrome wire. The battery sets up this electric field from the positive terminal to the negative terminal. If the electric field goes through a short wire then it will be strong and it will push the free electrons with a big force and so a lot of electrons will go through the short wire. If the wire is twice as long then the electric field will be half as strong as the shorter wire ,hence there will only be half the force pushing the free electrons and so half the current. In fact I will have doubled the resistance.
This is my table which I would set up to show my results:
Preliminary Work:
I did three preliminary experiments and I have included them with this work.
Proposed Method:
How will my preliminary work inform the plan:
In my preliminary work I used three different circuits to measure resistance. I found that the third experiment was the most effective because of the potential divider. With a potential divider you can get much more accurate control of the current of voltage.
In the light bulb experiment, I noticed that the filament got hot and so the resistance increased and therefore it is important to prevent the nichrome wire from getting hot and I will achieve this by keeping the current low.
Making the test fair:
I need to keep the temperature constant because if it was to increase then the resistance would increase so I must keep the current low.
I need to keep the material of the wire the same because each metal has a different resistance so I must use the same type of wire each time- I am going to use Nichrome wire from the same reel to ensure this.
I need to keep the cross-sectional area of the wire the same because thick wire has less resistance than thin wire and for my experiment I will use SWG 32 Nichrome wire.
Safety Precautions:
I need to take the following safety precautions during the experiment: ensure that I have dry hands whilst dealing with the electricity to prevent me from being electrocuted, wear gloves when changing the length of the wire so I won’t burn myself, keep a low voltage current to prevent the wire burning or getting hot and I must wear safety glasses when cutting the length of the wire to protect my eyes.
Detailed Procedure:
V
A
Results:
Analysis:
Interpretation of results:
My graph of resistance against length is a straight line that goes through the origin, which leads me to the conclusion that resistance is proportional to the length as I stated in my prediction:
If resistance is directly proportional to the length of the wire then my graph that I would draw from my results would look like this:
Resistance/Ω
Length of wire/cm
A directly proportional graph is a straight line graph that goes through the origin.
If I double the length of the wire then I will be doubling the amount of resistance. This is because the free electrons are pushed around the circuit because there is an electric field in the nichrome wire. The battery sets up this electric field from the positive terminal to the negative terminal. If the electric field goes through a short wire then it will be strong and it will push the free electrons with a big force and so a lot of electrons will go through the short wire. If the wire is twice as long then the electric field will be half as strong as the shorter wire ,hence there will only be half the force pushing the free electrons and so half the current. In fact I will have doubled the resistance.
This fully supports my original prediction, bearing in mind that I have only worked with one type of wire (Nichrome) and one thickness of wire (SWG 32) from 10cm to 100cm.
Evaluation:
I measured the length of the wire from 10cm to 100cm using a metre ruler with 1mm graduations. Because the metre ruler was calibrated at 1mm I could measure the length of the wire to one tenth of a centimetre.
This would introduce an error of about 1%
