- I found that with different lengths yielded very different results –
Using 10 amp range on meter –
With 50cm I got:
Cold Water:
Amps =0.1007
Voltage = 0.03
Resistance = 0.297 Ω
Hot water:
Amps = 0.1002
Voltage = 0.04
Resistance = 0.399 Ω
With 5m I got:
Cold Water:
Amps = 0.57 amps
Voltage = 1.43V
Resistance = 2.49 Ω
Hot Water:
Amps = 0.47 amps
Voltage = 1.45 V
Resistance = 3.085 Ω
With 10m I got these results:
Cold Water:
Amps = 0.0748
Voltage = 0.41
Resistance = 5.481 Ω
Hot Water:
Amps = 0.071
Voltage = 0.46
Resistance = 6.478 Ω
These results show me that using a longer wire is going to produce more precise results, I get more precise readings on the volt meter and amp meter which is going to produce more accurate resistance readings. To keep the result as reliable as possible I will do the experiment at least 3 times (ideally more if times permits) each time changing the wires/ equipment (apart from my testing wire) and take the measurements again. I am going to use a 10m length of enameled copper wire
Equipment I will need to use:
- Amp meter - I will need to measure the amps to find out the resistance
- Volt meter - I will need to measure the volts to find out the resistance . Variable Resistor - to keep the current of the circuit under 200mA so I can use the 200mA range on the Amp meter - this is because I can gain more precise results
- Batteries or power source - Obviously I will need to power the circuit, a power supply would be better as I always get the same voltage/current, these are not available so I will have to use batteries, the power they supply shouldn't make too much difference to the results
- Wires - to connect the circuit up
- Crocodile clips - to attach the wires to my ‘testing wire'
- Enameled copper wire - this is what I am testing the resistance of.
I will use temperatures from 0 °C – 100 °C if it is possible to achieve such extremes with a kettle and ice.
Graph:
When I come to collect my results I will need to plot a graph, I shall plot temperature (°C) along the X-Axis and Resistance (Ω) along the Y-Axis
Safety:
To keep my experiment safe I need to be safe around the kettle, to do this I will wear goggles to avoid hot water splattering into my face, make sure I have a decent sized work area so no-one knocks the kettle over. I will keep the batteries away from the water to keep them from short circuiting.
Method:
1. Get a piece of enameled copper wire and cut it to a length of 10m using wire cutters
2. Strip the enamel of each end with wet and dry paper
3. Check a current runs through the wire
4. Assemble the circuit as per the circuit diagram
5. Get ice in the water and lower the temperature as low as possible, take the first reading
6. Add hot water and take readings up until 100 °C (if possible)
7. Repeat the experiment after disassembling it and using new leads, multi meters, crocodile clips etc.
Conclusion:
The graph displays a strong linear correlation which is directly proportional: the higher the temperature, the higher the resistance. This is because as the temperature increases the atoms gain more energy meaning they vibrate more which leads to the atoms crystal lattice absorbing electrons thus making it harder for electrons to travel through the copper wire.
The gradient of the line of best fit (on the hand drawn graph) is 1.07645 this tells us that equation of the line is:
y = 1.07645x +c (the intercept)
My data shows me that the data could support a few lines of best fit, I have used excel to plot a scatter graph using the mean from all 3 sets of data and have used a logarithmic trend line which is obviously far better than just drawing one
The equation for this trend line is:
Y = 0.0203x + 5.0224
The Equation for my trend line (on my hand drawn graph) is:
Y= 0.025036
This tells us that mine is probably a bit too steep compared to the one on the computer.
The error bars are quite large, this tells us that my recordings were not very accurate or each time I changed the equipment the resistance in the wires etc varied a lot (I believe this to be the case). However for each set of data the differences between temperatures seem to be quite similar so I believe my method was quite reliable. I plotted a line graph on excel, for each line the data was 1 set of results, I wanted to see how the equations differed. This gave me a good idea of how reliable the results were.
1st set of data:
y = 0.0204x + 5.0838
2nd set of data:
y = 0.0207x + 4.976
3rd set of data:
y = 0.02x + 5.0074
The gradients are very similar to each other and are only a couple of decimal places off each other. This shows that the repeats were very reliable. The intercepts are quite close to each other, not as near as the gradients but pretty good thus meaning the measurements were precise.
Evaluation:
The equipment I used is only accurate to a certain degree and higher precision and accurate equipment could be obtained but obviously this is not available to me. A water bath for getting the temperature spot on would of increased precision of the readings. A more expensive multimeter would probably be more accurate in its reading due to its better calibration. The techniques I used allow for precise results however I think the enamel on the copper wire needs to be fully removed to the point where the wire has zero enamel on it as it might affect resistance; to do this I could use a Bunsen to burn it all off.
My graphs show me the error bars are quite large in places and small in others, this means that my results have not been very precise in the middle range of the graph, at the 2 extremities the range bars are very small and precise. I believe there is an anomalous result at the 80 °C Result – it seems to be very off from the rest of the results, none of the range bars are even on the line. With better experiment technique and better equipment I’m sure that the results would be much more precise.
It would be interesting to cool the copper wire to its critical temperature thus demonstrating superconductivity. Unfortunately copper is not a superconductor this is because copper electrons cannot cooper pair because copper’s tightly packed lattice constrains the vibrations needed for cooper pairing to take place. These characteristics are also displayed in gold and silver. According to the trend line calculated from the means copper would be no conductivity at -247°C – it would be interesting to test to see if there is any resistance at this temperature adding this to a the graph.
I think it would have been better to have a larger range of results so maybe - 100°C to 100°C using liquid nitrogen to cool it down to that temperature. This would be at 20°C increments.
I am quite confident in saying that my conclusion is accurate in the point that it declares that resistance is affected by temperature in a directly proportional way. The precision of my instruments makes me doubt the exact measurements I have taken, the thermometer is accurate to ±1°C. The multimeter is accurate to ±1mA however I highly doubt its precision (i.e. it’s not calibrated accurately).
