Physics Resistance of a Wire Investigation

Therefore, Ohms law says the more resistance means more energy used to pass through the wire. Resistance is a measure of how much energy is needed to push the current through something. The electrons carrying the charge are trying to move through the wire, but the wire is full of atoms that keep colliding in the way and making the electrons use more energy.

PREDICTION / HYPHOTESIS

I predict that if the length increases then the resistance will also increase in proportional to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Therefore, if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph should show that the Length is directly proportional to the resistance.

PLAN

In this investigation a simple circuit will be set up to read the voltage and current when the length of the wire changes. The length will range from 10cm - 100cm (1m) with intervals of 10cm. moving the crocodile clip across the wire on a ruler will change the length of the wire. I decided that the best thickness of wire to use would be 0.40 mm diameter of Nickel Chrome because it's a long, high resistance wire. This is because a thicker wire would cause too much heat, and the resistance of a thinner wire would be high and difficult to measure. The reason for this is that a thicker wire has less resistance, because there is more room for the electrons to travel through it.

The circuit should be set up as in the circuit diagram. It is important that the voltmeter is set up in parallel and the ammeter in series. The readings from the ammeter and voltmeter will be used to work out the resistance.

Where V=voltage, I=current and R=resistance.

The resistance is going to be recorded at 10 different lengths. I have chosen to record the results at this amount of lengths, as it will give me a much more accurate result at the end of the experiment.

The way to calculate the Resistance relies on this formula:

Resistance = Voltage/current

I will use the Voltmeter provided to get the voltage, and the ammeter provided to get the current (in amps).

APPARATUS

Power supply

Nickel Chrome wire

Crocodile clips

Board

Voltmeter

Ammeter

Connecting wires

METHOD

. Arrange apparatus as shown in the Diagram:

2. Attach the wire to the crocodile-clip leads and set voltage.

3. Take the reading from the ammeter and record in results table.

4. I took 7 different readings for each length of wire and find the Resistance of it.

5. Write down the results in a table.

6. Then work out the resistance using the formula V÷I=R

(Voltage ÷ Current = Resistance)

7. With the results obtained, plot some graphs.

8. See if my prediction was successful or not.

I used a board were Nickel Chrome is placed in three different rows, each one with different diameters, and I used only one, 0.40 mm diameter. The board is divided every 10 cm.

RESULTS

0 cm

V/V

IA

R/Ohms

0.7

.42

.3

0.84

.54

20 cm

V/V

I/A

R/Ohms

.5

0.57

2.63

.6

0.62

2.58

.7

0.66

2.57

.9

0.73

2.6

R = 2.56 Ohms

30 cm

V/V

I/A

R/Ohms

.7

0.46

3.69

.9

0.53

3.58

2.1

0.54

3.88

2.4

0.65

3.69

2.5

0.66

3.78

R = 3.63 Ohms

40 cm

V/V

I/A

R/ohms

.8

0.41

4.39

2

0.45

4.44

2.2

0.47

4.68

2.4

0.51

4.7

2.6

0.57

4.56

2.9

0.59

4.91

3

0.62

4.83

R = 4.5 Ohms

50 cm

V/V

I/A

R/Ohms

.9

0.35

5.43

2.2

0.4

5.5

2.5

0.43

5.81

2.7

0.48

5.63

3.1

0.54

5.74

3.4

0.59

5.76

3.6

0.63

5.71

R = 5.4 Ohms

60 cm

V/V

I/A

R/Ohms

2.1

0.29

7.24

2.5

0.35

7.14

2.8

0.39

7.17

3

0.41

7.31

3.3

0.44

7.5

3.5

0.48

7.29

3.8

0.52

7.3

R = 7.46 Ohms

70 cm

V/V

I/A

R/Ohms

2.2

0.28

7.86

2.5

0.3

8.3

2.9

0.35

8.29

3.2

0.4

8

3.5

0.42

8.3

3.8

0.45

8.4

4.1

0..5

8.2

R = 8 Ohms

80 cm

V/V

I/A

R/Ohms

2.3

0.23

0

2.7

0.28

9.64

3.1

0.32

9.69

3.5

0.36

9.72

3.7

0.4

9.25

4.1

0.42

9.76

4.5

0.46

9.78

R = 9.71 Ohms

90 cm

V/V

I/A

R/Ohms

2.3

0.22

0.45

2.7

0.27

0.00

3

0.29

0.34

3.3

0.3

1.00

3.6

0.36

0.00

4

0.4

0.00

4.5

0.45

0.00

R =10 Ohms

00 cm

V/V

I/A

R/Ohms

2.5

0.24

0.42

3

0.27

1.11

3.5

0.32

0.94

4

0.36

1.11

4.5

0.41

0.98

5

0.45

1.11

5.5

0.5

1.00

R =11.11 Ohms

ANALYSIS

Summary Table

Length/cm

Resistance/Ohms

0 cm

0 Ohms

20 cm

2.56 Ohms

30 cm

3.63 Ohms

40 cm

4.5 Ohms

50 cm

5.4 Ohms

60 cm

7.46 Ohms

70 cm

8Ohms

80 cm

9.71 Ohms

90cm

0 Ohms

00 cm

1.11 Ohms

The results from the graph give a clear indication of how the resistance compares to the wire length. There is a very strong positive correlation. This means that when the length of the wire increases, the resistance also increases. The results are also directly proportional, meaning that when one doubles so does the other. An example would be at a wire length of 20 cm, the resistance is 2.3Ohms and at 40 cm it is 4.6Ohms. This is exactly double the size.

The theory behind this is explained in the prediction. In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional.

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. I also said that the link should be directly proportional. The results have shown that this is true.

The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.

Extrapolation: I think that the best fit line will still be a straight line, because as we can see and mentioned before, as the length increase, the resistance does as well.

I think that my results are suitable to confirm my prediction.

EVALUATION

This experiment has gone satisfactory, but there have been certain things in the experiment that I have not been pleased with.

For instance, I think it would have been better if a used a digital voltmeter rather than a conventional voltmeter because its more accurate.

It could be improved by trying other lengths, different voltages but also a different type of wire to be able to compare the resistance difference this would make a more interesting experiment.

Also, I think it would have been better if I repeated the experiment twice so that I have more results and can compare it better.

In the experiment, I did not control the room temperature but instead just assumed it was keep constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate.

I think the circuit and method used was quite suitable although I would make the modifications above to improve my results.

CONCLUSION

In conclusion, I have found that my prediction was correct. I said that the resistance will increase approximately proportionally to the length, and as you can see from the graph, this was correct. This is emphasised because the line of best fit is a straight line, which means the resistance is proportional to the length. This proves the fact that the longer the wire is; the more collisions there are between atoms and electrons. So if the wire increases in length, so does the resistance. If the wire decreases in length, so does the resistance.

Antonella Turci