The factors, which I am going to keep constant, are as follows:
The width of the cylinder of putty
The voltage running through the circuit
The shape of the putty
The following apparatus is to be used for this experiment:
D.C. Power Supply
Ammeter
Voltmeter
Variable Resistor
Resistance Putty
Wires (some may need to have crocodile clips attached to them)
2 x 2 pence pieces
To set this experiment up you will need to follow the following method carefully:
Collect all equipment (shown in list above)
Roll the carbon putty to a 30cm cylinder, making sure the diameter is constant all of the way along the cylinder
Attach one of the two pence pieces to each end of the cylinder of putty.
Set up the circuit, carefully following the diagram above to make sure that all of the equipment is in the correct place.
Once the equipment is set up correctly, make a record of a reading of the resistance, and then repeat this reading twice, this is to make sure that none of your readings have been taken incorrectly, and that it is the correct sized cylinder, you could also measure the weight of the putty.
Cut the putty to a length of 27cm and re-measure the diameter to make sure that it is the same diameter as used for the last reading
Repeat the last bullet point for the other five different lengths (25cm, 20cm, 15cm, 10cm, 5cm)
The safety procedures to be considered during this experiment are:
Don’t touch the circuit with wet hands
Make sure that there aren’t any gaps in the insulating plastic, before connecting to a power supply.
Don’t run a too high voltage through the circuit, until you are sure that it is safe to do so.
Do not override the power supply.
This is a list of the Equipment I used, and what I used it for:
I will now plot a graph of the average current measured for each length.
I will now take my results and find the resistance, and the average resistance.
V = I x R
Voltage = Current x Resistance
Rearranged to give:
R = V
I
Resistance = Voltage
Current
I will now plot a graph to show the average resistance:
My results show that my prediction was correct. I predicted that the shorter I cut the putty, the lower the resistance will be. The longer the length of putty, the higher the resistance will be. This is because there are more atoms in a larger cylinder of putty than there are in a smaller piece of putty, this therefore means that in the larger cylinder of putty there is more chance that the electrons will collide with one of the atoms, therefore there is more resistance.
My graph shows that the resistance steadily increases as I steadily increase the length of the resistance putty.
The graph below shows a line of best fit for the average resistance:
In conclusion, I have found that the more of the resistance putty there is the higher the resistance will be. This is because conductors have lower resistance when they are shorter this is because the electrons have a shorter distance to travel therefore more energy is conserved since there are fewer collisions, and the current is higher. Resistance is inversely proportional to cross-sectional area because if the cross-sectional area is increased then the electrons can move faster and therefore current is increased. Resistance and cross-sectional area can be considered similar to water travelling through a tube, the wider the tube the faster water can travel through it and the speed of the water is limited by the area of the tube with the lowest cross-sectional area. Therefore this shows that my prediction was correct (I predict that the shorter I cut the putty, the lower the resistance will be. The longer the length of putty, the higher the resistance will be. I think that this is because there are more atoms in a larger cylinder of putty than there are in a smaller piece of putty, this therefore means that in the larger cylinder of putty there is more chance that the electrons will collide with one of the atoms, therefore there is more resistance.)
I think that my results have given me enough evidence to show that my prediction is correct. My results are very good and have no mistakes within them.
I think that this was a suitable procedure to use to investigate resistance, as it showed what I needed to know very clearly, but if I could re-do this experiment another time, I would take more sets of results, in order to be more accurate with my results. I think that therefore, I can rely on my results answer my earlier question of ‘how does resistance depend on shape’ thoroughly and correctly.
