When changing the width of the paper, the variables I will have to keep constant are: -
- The length of the graphite paper.
- The temperature of the graphite paper.
- The voltage.(For the investigation of current and width)
When changing the temperature of the paper, the variables I will have to keep constant are: -
- The length of the graphite paper.
- The width of the graphite paper
Predictions
I predict that when the width of the graphite paper is made smaller, the current will go down. This is because making the paper less wide will reduce the amount of free electrons; therefore not as much current is able to pass through it. As resistance equals voltage over current, when the width of the graphite paper goes down, the resistance will go up.
I also predict that when the width is doubled the current will double. This is because doubling the width doubles the amount of free electrons, doubling the current.
I also predict that when I halve the width, the resistance will double. This is because halving the width would make it double as hard for electricity to pass through it, doubling the resistance.
Below is what I expect my graphs to look like.
I predict that when I increase the temperature, the resistance will go down. I believe this to be the case because on page 245 of Physics by Hutchings it says that carbon has a negative temperature coefficient of resistance. Graphite is a form of carbon, and should behave in the same way.
Below is what I expect my graph to look like.
Method 1 (width of paper)
Apparatus.
7 wires.
Ammeter
Voltmeter
Variable resister
2 Cells
2 pieces of Graphite paper
Scissors
2 Modified bull dog clips
Circuit Diagram.
- Measure the width of the graphite paper, and draw 7 lines of equal distance from each other along the length of the paper.
- Set up the circuit (see diagram above)
- Place the graphite paper in the bulldog clips.
- Alter the variable resister to make the p.d 1 volt.
- Take the graphite paper out of the clips and cut with scissors down the next line.
- Repeat stages 3-5, until you have 7 readings.
- Divide the voltage by the current to give resistance.
- Repeat the whole experiment with two cells, but altering the variable resister to make the p.d two volts.
I will use an analogue ammeter as it gives a more accurate reading.
Method 2 (temperature of paper)
Apparatus
Wires
Emersion heater
Large beaker
Graphite paper
Water
Thermometer
Ohmmeter
2 Modified bull dog clips
Circuit Diagram
- Take a piece of graphite paper; attach a modified bulldog clip to each end. Wrap around the beaker, and secure with tape.
- Attach an ohmmeter to the bulldog clips using 2 wires.
- Heat up the water using an emersion heater to the first chosen temperature.
- Wait about a minute for the paper to heat up and take the reading on the ohmmeter.
- Change to the next chosen temperature.
- Repeat stages 4 & 5 until you have all your readings.
Analysis 1 (width of paper)
By looking at graphs 1 & 2, I can deduce that when the width of the graphite paper goes down, the current decreases. This is because making the paper less wide will reduce the amount of free electrons; therefore not as much current is able to pass through it. On graph 1, when the width of paper was 6 cm, the current was about 0.00050 amps. When the width of the paper was decreased to 4 cm, the current was 0.00030 amps.
By looking at graph 3, I can see that when the width of the graphite paper goes down, the resistance goes up. When the width of the graphite paper was 6 cm, the resistance was about 1800Ω. When I shortened the width of the paper to 1 cm, the resistance went up to 20000Ω.
I predicted that when the width of the graphite paper is made smaller, the current would go down; and when the width of the graphite paper goes down, the resistance will go up. As you can see above, both of these predictions were correct.
I also predicted that when the width is doubled the current would double. By looking at Graph 1 when the width of the graphite paper was 2 cm, the current was 0.00014 A. When the width was doubled to 4 cm, the current doubled to 0.00030 A. Although the current did not double exactly, it is well within reasonable experimental error.
Current is proportional to width since plotting a current against width produced a straight line through the origin.
I also predicted that when the width of the paper was halved, the resistance would double. If you look at Graph 3, when the width was 6 cm, the resistance was 1818Ω. When the width was halved to 3 cm, the resistance roughly doubled to 4000Ω. This is well within reasonable experimental error.
Analysis 2 (Temperature of paper)
By looking at Graph 4, I can see that when the temperature of the graphite paper is increased, the resistance goes down. When the temperature was 40 C, the resistance was 1.410 KΩ. When the temperature was increased to 80 C, the resistance decreased to 1.263 KΩ. This supports my earlier prediction that that when I increase the temperature, the resistance will go down.
Evaluation 1 (width of paper)
I think that my experiment worked well because my results were consistent with each other. I received no anomalous results, which must mean that my investigation was a success. However I cannot say that my results were perfect. They were not all exactly on the same line of best fit in either graph 1 or 2. In my experiment I used scissors to cut down the graphite paper. I could improve on this by using a guillotine. This would make sure that the graphite paper was of a consistent width the whole way down.
I could also use a narrower range of values for the width of the paper; maybe go down in 0.5cm instead of 1cm.
Nevertheless, my graphs allowed me to draw a decent conclusion from the experiment (see analysis) and see a pattern, and see quantitatively what the pattern did.
Evaluation 1 (temperature of paper)
I again think that my experiment worked well because my results were consistent with each other. I received no anomalous results, which again must mean that my experiment was a success. However my results were not perfect as the points did not all lie on the same line. This could be because of the condensation, which would have slightly dampened the paper, altering how much current can pass through it. To improve the experiment you could wrap the paper around a light bulb to heat it, and use a variable resister to change the temperature. But it would be difficult to measure the temperature of the paper.
Nevertheless, my graph allowed me to draw a decent conclusion from the experiment (see analysis) and see a pattern, but I could not see quantitatively see what this pattern did.