Variables Why controlled? How controlled?.
Length of wire The resistance changes with the length of wire. There are different amount of electrons in different length if wires. This will affect the accuracy of results if the wires are not measured properly. This is an independent variable. I will use a metre stick to measure the wire at eye level for accuracy.
The wire must be pulled tight and held into place while measuring to ensure the length is accurately measured.
Current We need to keep the current the same throughout the experiment because we are not measuring the current. We are investigating the resistance. This is a controlled variable. We will use a variable resistor to keep the current at a constant measure. We are going to keep the current at 0.3 amps.
Resistance This is a dependant variable because this is what I want to find out about. This is not controlled. We are going to measure the resistance by using a voltmeter and ammeter. We work out the resistance by the formula: .
Resistance (ohms, Ù) = Voltage (volts, V).
Amps (A).
I will calculate this by using a calculator so I avoid any possible errors.
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Fair Test.
The only variable that I will be altering will be the length of the wire as this is the main variable. The other variables, I will keep controlled to make it a fair test. I will keep my controlled variables the same by making sure that I have implied the same strategy for each experiment. The length of the wire is going to be controlled by using a metre stick, and the current is going to be controlled by using a variable resistor - this can change the current to any number, but we are going to keep the current at a constant measure (0.3 amps) to make it a fair test. I will also do all calculations using a calculator (averages, finding the resistance). Each experiment should be repeated 3 times to make sure the results are reliable and accurate.