When a different material is used the resistance changes. This table is also from preliminary work I carried out. It shows that the resistance is different in each material because there are a different amount of atoms in each one.
I chose Nichrome wire because it has resistance in the middle of the other two wires so that it makes a fair test.
Apparatus
- Digital Voltmeter
- Digital Ammeter
- Power Pack
- Crocodile Clips
- 5 Different lengths of constantan wire
- Meter Ruler
- Heat proof mat
Diagram
Method
- Collect apparatus
- Set up 20cm wire in circuit (as shown in diagram)
- Measure voltage across the wire at 0.2 and 0.4 amps
- Calculate resistance
- Repeat 2,3,4 with 40 60 80 and 100cm of constantan wire
Scientific Evidence
In a piece of wire atoms are arranged in a regular pattern called a lattice. The positive charges are concentrated in the nucleus and are unable to move. The negative charges (electrons) are freer to move. They normally flow haphazardly without direction. If a cell is connect the electrons flow to the positive terminal (+ve). This flow of charge creates an electric current
When the electrons in a current move in the circuit they collide into atoms in the wire. This causes a heating effect so in the experiment I will keep the current below 0.5 amps. Atoms of different material hold up the electrons by different amounts
Results
0.2A
0.4A
Averages
Second Method
Method 2 is the same as the first method but instead of using an Ammeter and Voltmeter. I used a Multimeter since the Multimeter has it’s own power supply there was no need for the power pack. This method will show if the attached devices cause the resistance to change. I set up the method as.
Results
Analysis
When I doubled the length of the wire the resistance doubled. From my first set of results when the length was 20cm the resistance was 0.85 ohms and when the length was 40cm the resistance was 1.65 ohms. This shows that the resistance doubles when the length doubles my graphs also support this conclusion and they show a strong correlation. When the length of the wire is doubled there are twice as many atoms for the electrons to collide with causing a double resistance. The results that I have obtained support my original prediction. This is because in the prediction I said that as the wire length increased, the resistance should increase. The results have shown that this hypothesis is true.
The line of best fit clearly shows that the results followed the predicted pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional because the gradient stays the same
Evaluation
From my results I found an odd result in each method. 20cm in method one and 80cm in method two. These are marked on my graphs. The ammeters and voltmeters could have been damaged and reading falsely on both the meters used. Measuring the lengths of the wire is also an inaccuracy as the rulers used are not likely to be exact, and it is difficult to get an accurate reading of length by eye, as the wire might not be completely straight and have kinks in it. These could have contributed to the odd results.
If I had more time I would repeat the experiment twice and be more careful in taking my results and plotting my graphs taking temperature, voltage, length of wire, diameter of wire and resistance of the circuit into consideration a lot more as this will improve the reliability of the experiment. There are different results in both methods. This is because the Multimeter has its own power source and there will be less components putting resistance into the circuit, so the resistance should be less for Method 2 than Method 1 so Method 2 will have more accurate results.
