GCSE physics coursework: Resistance of a wire
Scenario:
Jack has been given a second hand D.C. dynamo and lamp. He wants to attach these to his bicycle and produce most light without blowing the bulb.
What wire should he use?
Variables:
The variables in our investigation are…
- The length of the wire
- The diameter of the wire (SWG)
- The type of wire
Types of wire:
Nichrome: 80% Nickel 20% Chromium Alloy.
Constantan: 60% Copper 40% Nickel Alloy.
Copper
First of all we decided to test the resistance using a Multimeter. This would give us a rough idea about what the resistances of each wire are.
Our lengths of wire were all 30cm long.
Our results were as follows…
Later we realised that we were using wires with completely different SWGs.
To make it a fair test we needed to use wires with the same SWG.
We repeated the test using a length of 30cm and an SWG of 32.
Our results were as follows… Our results changed dramatically.
Testing the current + Voltage
Next we decided to test the current and voltage so that we could get a more accurate figure for the resistance.
We set up a circuit consisting of, a power pack, ammeter and variable resistor in series. We also had a voltmeter in parallel to the wire we were testing.
The readings we take off the ammeter and voltmeter allow us to figure out the resistance using a simple equation: Voltage ÷ Current = Resistance.
Our circuit looked like this…
A variable resistor allows us to control the current going through the circuit. We needed to keep it as low as we could to avoid a heating effect in which ohms law would not take place and our results would not be accurate.
After we got these results we decided constantan would be the best wire to use as it would not get hot and affect the accuracy of our results or burn up like copper and its resistance is also not too high like Nichrome. After completing this experiment and choosing our wire we decided to test which diameter wire is the most effective.
For testing diameter we used the same circuit as we did for testing the different types of wire but this time the variable is the diameter.
The diameters we had chosen to use were 18 24,26,32,34 SWG (Standard Wire Gage).
We were testing to see which diameter had least resistance but would not bur up or get to hot. Each wire was 30 cm long and our results were as followed ….