Predicting:
The longer a wire, the greater its resistance. This is because the charges have further to go through the material; there is more chance of collisions with the atoms of the material
Selecting the most suitable apparatus:
For my experiment I will use metre rule, ammeter, voltmeter, battery and copper wire. metre rule: I will use it to measure the length of the copper wire Ammeter: I will use it to measure the size of a current flowing through the wire. The electric current flowing through the circuit is measured in amperes or amps. It does not matter where to put the ammeter in the circuit because the current is the same everywhere. The ammeter has to be connected in series, it is important to connect an ammeter so that its red (+) terminal is always nearer to the positive pole of the cell than to the negative pole. Voltmeter: Is used to measure the potential difference (p.d.) it is measured in volts (V). The voltmeter must be connected in parallel, across a component (nichrome wire). As with an ammeter, the voltmeter must be connected the correct way round (positive to positive). To get accrued readings I will have to use digital ammeter and voltmeter. Battery: Is useful source of electricity. It transfer chemical energy to electrical energy. Copper wire: Is a good conductor of electricity so I will use it in my experiment.
Number and range of my readings:
I will take 10 readings, the minimum length of the wire is going to be 5 cm and the maximum 50cm. I will start from 50cm and every time the length will decrease by 5cm. To make my results more reliable I will repeat the test starting from the minimum length (5cm), and then find the average. To get more reliable result I should have to repeat the experiment again and find the average of both readings.
Safety:
Do not short circuit the wires. And do the preliminary runs so that the wire does no overheats.
Preliminary run: When I tried to take a reading for the length of 5cm the wire heated up and I got strange readings. The wire heated because a potential difference across the material causes free charges inside to accelerate. As the charges move through the material, they collide with the atoms of the material which get in their way. They transfer some or all of their kinetic energy, and then accelerate again. It is this transfer of energy on collusion that causes electrical heating. To prevent this I will use thicker wire because there is a bigger area for the charges to travel through, with less chance of collision. Infact the resistance is inversely proportional to the cross-sectional area of the wire.
Conclusion:
When I found the current and the potential difference for different lengths I used Ohm's Law R=V/I (resistance=potential difference/ current) to find the resistance. Plotting points on a graph resistance vs length and drawing a line of best fit, showed me how resistance and length
Increase proportionally to each other. The electric current in the wire is the flow of electrons. When the wire gets longer electrons will have to travel longer distance and loose more energy therefore resistance is proportional to the length of the wire. This supports my prediction.
Evaluating:
All the points were near the line and there was no strange points compare to the others so I think that my readings were accurate.
