2) Length of wire The larger the length of the wire, the larger the resistance. This is because there are more atoms from the metal so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance. The length of wire will be variable throughout the investigation. Electrons have a longer distance to travel when the wire is longer, so there are more collisions .The length of the wire will make a difference to the resistance. 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.
3) Type of material l Different materials have different resistances because the materials' atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire. Throughout the experiment Constantan will be used. The type of material will affect the amount of free electrons that are able to flow through the wire. The number of free electrons depends on the amount of electrons in the outer shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase of the number of electrons. If the particles in the material are tightly packed together, the electrons will have more collisions and therefore more resistance.
4) Diameter/Cross sectional area A good example to illustrate this where two cars are travelling down a dual lane road side by side. As soon as the road changes to become a single lane road, it is impossible for the cars to travel side by side and one must stop and resume behind the other car. This same can be said for electrons in a wire, the larger the diameter/cross section, the more electrons are able to travel trough the wire at the same time.
Apparatus
Ammeter
Voltmeter
Power supply
Crocodile clips
Constantan wire
Meter ruler
Conductible metal to vary the length of constantan
Method
- Gather up listed equipment
- Create a circuit with the constantan wire in it
- Use the metre ruler to mark out 10cm intervals to 100cm
- Measure the voltage in the voltmeter and the amps in the ammeter.
- Record the readings. Calculate the resistance using R= V/I
- Allow time for wire to cool down
- Repeat the experiment at a different interval and for a 28 swg wire
Safety
Be careful when touching the wire, as it may be hot.
Start on the lowest current, so the wire then will not melt or burn instantly.
Be careful when the wire is connected, as it will get hot.
Make sure the mains to the power supply is switched off when removing the wire from the circuit to be measured. Keep my work area clean and tidy to avoid confusion.
Handle the power supply carefully.
Fair Test
The wire must be the same thickness,
The surrounding temperature must be constant, or near enough constant, so the experiment should only be done on one day,
The equipment should be kept the same, Only change the length of the wire and thickness when using the second wire.
Prediction
I predict that if the length increases then the resistance will also increase in proportional to the length.
I think this because, as I have explained above in my background knowledge, the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. If I had a 30 cm wire and a 60 cm wire, the 60 cm wire would have a resistance twice that of the 30 cm wire. Therefore, if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph should show that the Length is directly proportional to the resistance.
If the length of the wire is only half the length of the wire on the same type of wire, there should be half the number of collisions between the electrons and the atoms.
If the wire is twice as long, there should be twice the number of atoms, resulting in twice as many collisions and a predicted doubling of the resistance.
