To investigate how the length affects the resistance of a wire.

3.Wire length:

If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase.

4.Wire width:

If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

In my investigation I will be investigating how the length of the wire effects the amount of resistance.

Prediction:

I predict that if the length increases then the resistance will also increase in proportion to the length. I think this true as I know from my scientific knowledge that:

Electric current is the movement of electrons through a conductor. In this experiment a metal wire (Nichrome) will be the conductor. So when resistance is high, conductivity is low. Metals such as Nichrome conduct electricity well because the atoms in them do not hold on to their electrons very well. Resistance is when these electrons which flow towards the positive collide with other atoms, they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means the resistance is doubled.

My graph should show that the length is directly proportional to the resistance.

Predicted graph :

The factors that I will keep the same during this experiment are:

) The temperature

2) The thickness of the wire

3) The type of wire

Safety Precautions :

There are not many safety precautions that need to be taken into consideration, in this experiment. The main two I can think of are stated below:

) Do not carry out the experiment in wet areas, as water is a very good conductor, and thus could be very dangerous.

2) Do not touch the wire when the battery pack is switched on, because the current would heat up the wire.

Apparatus :

) Battery pack

2) Nichrome wire

3) Meter Ruler

4) Crocodile Clips

5) Sellotape

6) Connection Lead

7) Ammeter

8) Voltmeter

I set up my experiment as shown above.

I started the experiment by sellotaping the Nichrome Wire (over 1 meter long) to the meter ruler. I then connected the battery pack the thee ammeter using a connection lead. The ammeter was then connected to the wire using a connection lead and a crocodile clip. Then I connected this to the voltmeter and back to the battery pack. The teacher checked this for safety. When it was checked a table was written to record the results. The battery pack was switched on next. The resistance was then recorded down for various lengths ranging from 0 - 100cm. After each measurement was taken the battery pack was switched off to ensure the wire didn't heat up. If it had heated up to much the particles in the wire would move faster and create moere resistance, therefore effecting the results. I then plotted these results on a graph.

To collect the data for my graph I had chosen to take a range of 6 lengths. I had chosen a range of 6 as to plot an accurate graph I will need at least 5 points to mark on the graph. The lengths that I had chosen were as follows: 10cm, 20cm , 40 cm, 60cm, 80cm, 100cm. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results.

I will to three experiments repeating my results twice. This is to ensure a fair test and get a range of results. I will then work out a mean for each test.

Results :

Test no.

Length (cm)

Voltage (volts)

Currents (amps)

Resistance (ohms)

Mean

Test no.

Length (cm)

Voltage (volts)

Currents (amps)

Resistance (ohms)

Mean

Test no.

Length (cm)

Voltage (volts)

Currents (amps)

Resistance (ohms)

Mean

I plotted these results in a graph:

Conclusion:

The graph is a straight line through the origin, which means resistance is directly proportional to length. This means that if the length is 40cm, and resistance is 4 ohms, then if length is doubled to 80cm, resistance also doubles to 8 ohms.

This is because of the scientific idea that if you double length, you double the number of atoms in it. The results support my predictions well. They turned out the way I had expected and match the predicted line well. I had predicted a straight line through the origin.

Evaluation:

From my graph I can see that my results that I collected are reliable. I know this because my graph shows very few individual odd results. I can see on the graph that not many of the results plotted are odd because all the points lie along the same straight line.

When I was measuring the lengths of the Nichrome wire my measurements might have been slightly inaccurate. This is because it was difficult to get an accurate reading of length by eye, as the wire was not completely straight. This would have contributed as a slight error in my results. As this factor probably only made a slight difference, it did not affect my results.

To make my experiment possibly more accurate I could have got 3 sets of results and found an average but this would be too time consuming.

I don't think I could really improve on the way the experiment was done because my results were quite accurate, as I had hardly any odd results.

I also found that the experiment was quite easy to set up, as it was simple and uncomplicated.

Further experiments I could do related to the resistance in a wire would be to see whether the following factors would make a difference in the resistance of a wire:

) Wire width:

I think that if the wire width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

2) Temperature:

I think that if the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.

3) Material:

I think that the type of material of the wire will affect the amount of free electrons, which are able to flow through that wire. This is because the number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high numbers of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.