Apparatus List
Wire Micrometer screw gauge
Power pack Ammeter (10 amps)
Crocodile clips Voltmeter (20 volts)
Leads Ruler (1 meter)
Safety
To keep my experiment safe I will follow these rules
Don’t use short wire – short wire will burn
Don’t leave P.S.U. on – wire will burn
Put bags and chairs out of the way
Keep water and other objects away from experiment
Fair Test
To keep my experiment fair these factors must stay the same
Same material- (Constantan wire) Different conductors can alter results
Same equipment-Different voltmeter and ammeter could alter results
Same thickness-Same thickness of Constantan wire
Same temperature-This alters the results (room temperature)
Same current-This alters the results
Method
- Set up the circuit
- Attach the constantan wire to the meter ruler
- Clip one crocodile clip on 0cm and one on 100cm
- Turn the dial on the P.S.U. until the reading shows 1 amp on the ammeter
- Measure and record the reading on the voltmeter
- Repeat this reducing the distance by 20 cm each time until the distance is 20 cm
- Repeat steps 1-6 twice more for repeat readings
- Calculate the resistance using R=V/I
Range of Values
I am using 20cm – 100cm of constantan wire
Preliminary Work
I carried out the experiment to determine the length of constantan wire to use and I found out that the length of wire under 20cm heated up to a high temperature and under 5c m melted.
Results
Analysis
The results show that the larger the wire the greater the resistance
Trends and Patterns
We identified patterns and trends from the line graph which shows that the graph is a directly proportional relationship because it passes through nought and is a straight line. Also when the length doubles the resistance doubles for example: 20 cm is 0.93 ohms and 40 cm is 1.82 ohms. So these results prove that.
Conclusion
The free electrons in the wire leave the atoms and flow through the wire causing the atoms to become positive ions.
From our experiment we found out that when the length increases the resistance also increases this is because the free electrons in the wire which are travelling in random directions are colliding with more ions and electrons. So the electrons transfer kinetic energy causing the ions to vibrate more vigorously generating heat. The transfer of kinetic energy means that the electrons ‘lose’ more energy causing the voltage to increase. V=E/Q voltage = energy/charge . V=I/R voltage = current/resistance. So our prediction ‘the longer the wire the greater the resistance ‘is correct in the way that as the length increased so did the resistance.
Evaluation
Our procedure was good we worked in a systematic way starting from 20 cm working our way up to 100 cm and then repeating our experiment three times. Our evidence was good as well with only one anomaly which we repeated to give a more precise result. I think we had an anomaly because it is extremely difficult get the current 1 amp on the ammeter and when we read the ammeter the current could have changed. The results are reliable because the averages are all close together proving that they are not anomalies. We could improve the experiment by being more accurate on the wire by attaching a thin wire to each crocodile clip reducing the area touching the crocodile clip so our measurements would be more accurate. The results are compatible with the conclusion because they matched up even with anomalies. To do further research I would get five different thickness of wire set up the circuit as before. But change the thickness instead of the length and keep the length the same and measure the voltage.
