How can I change the resistance of a wire?

Physics Coursework

Introduction:

Electricity is conducted through a wire, it moves using free electrons – the amount of free electrons depends on the type of wire, the more free electrons the more conductive the wire. Free electrons are what are called ‘given energy’ so they move and collide with other free electrons beside them. These collisions or ‘jumps’ as they are sometimes called; occur all the way down the wire, and this is how electricity is conducted. Each time they collide it converts some of the energy the free electrons have in to heat. And that is what RESISTANCE IS THE RESULT OF KENITIC ENERGY LOST AS HEAT.

Ohms law is also quite important to this; in 1826, George Ohm discovered that: the current flowing through a metal wire is proportional to the potential difference across it (providing the temperature remains constant). It says that the current is proportional to the voltage. So if you double the voltage the current doubles to. This also comes into play with the length of the wire, if you double the length of wire, the resistance doubles too.

The thickness of the wire of the wire also affects it to, if you have some very thin wire then the resistance is higher, this is because there aren’t as many free electrons to collide with. But with a thicker wire the resistance is lower because there are a lot more free electrons to collide with in the wire.

A circuit is made when wires connect to the battery with no gaps this is a circuit.

Electric current flows out of the negative side of the cell and around the current through the wires and back into the wire on the positive side. We will be using direct current, which is when the current flows in just 1 direction around the circuit.

Simple procedure:

First I would get a meter ruler then I would stretch a wire from one end to the other and tape it at both ends, I would put a ...

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A circuit is made when wires connect to the battery with no gaps this is a circuit.

Simple procedure:

First I would get a meter ruler then I would stretch a wire from one end to the other and tape it at both ends, I would put a crocodile clip at one end of it to connect it to a circuit as in the diagram). To change the length of the wire I put a crocodile clip on the other end of the circuit so I can clip it at different lengths along the wire. I would take readings of the voltage across the wire and current in circuit.

Prediction:

I predict that as the length of the wire increases the resistance will increase proportional it. So if I doubled the length of wire the resistance would also double. I think this is because as the length doubles the number of atoms doubles, making double the number of collisions, so the resistance should also double. This is because the number of electron jumps – which take up more energy, will also double, which will result in a greater resistance. All this slows the electrons down, increasing the resistance. My graph should show that the length is directly proportional to the resistance by a straight line of best fit.

Variables:

Length of wire,
Type of wire,
Temperature of room,
Thickness of wire,
Temperature of wire,

I shall be investigating the length of wire.

Range:

The range I have chosen is:

Safety points:

I am using very low voltages so there is no risk of electric shock, and I shall not leave the power on for very long which will stop any over heating.

Equipment:

Meter of Constantine wire,

Meter ruler,
Variable resistor,
Ammeter,
Voltmeter,
Crocodile clips,
Copper wire,
Variable power source,

Method:

First I got a meter ruler and stretched a meter of Constantine wire and taped it down at both ends. I then set up a circuit as in the diagram, complete with an amp meter and a voltmeter. I connected the wire at one end with a crocodile clip to the circuit and at the other end of the circuit I put a crocodile clip so I can change the length of nichrome wire in the circuit. For the first of the range, I put the second crocodile clip onto the wire at 10cm as marked on the ruler. I turned on the power. I took the voltage and the current readings then I turned off the power. I did this for each length in the range and repeated the experiment 2 more times so it’s accurate.

Diagram:

Preliminary work:

I did a preliminary test so I could see if the experiment produced useful results. I tested two lengths of wire and if there is a noticeable difference between the 2 then the experiment will be a success.

I have decided not to change the method of carrying out this experiment because the results suggest that there is a noticeable difference.

Results:

Conclusion:

I can see from the graph that my results are all reasonably close to the line; there aren’t any totally obvious anomalous results. I can see that the level of resistance goes up, as the length of wire gets longer, this shows that the length is directly proportional to the resistance. Which makes what I stated in the prediction is right, what I said in the prediction is - if I doubled the length of wire the resistance would also double.

On the graph I have started to calculate the gradient. The formula for this is

G = rise / run

G = 1.75 / 38

G = 0.046

G = 0.05

This shows that for every 1cm moved along on the graph that it goes up 0.05Ω. This shows that the resistance is directly proportional to the length, at 10 cm the resistance is 0.5 ohms, and at 20 cm the resistance is 1 ohm. So when the length doubles the Resistance doubles.

So resistance = 0.05 * length of wire.

Evaluation:

I have a lot of confidence in my results; I think that I have collected them quite accurately. There doesn’t appear to be any results that are very out of place, they are all close to the line of best fit. I think the experiment procedure made the best use of the equipment available to me. My prediction was also pretty accurate, so I have a lot of confidence in that also.

To make the results more accurate I could have used digital voltmeters and ammeters because I could have easily made errors when reading off the measurement, a digital one would give an exact number with decimal places that I would not be able to read off the normal meter. If I had used something more like a knife blade, instead of crocodile clips – which are quite wide, to clip the wire then the measurement of wire would have been much more accurate. The wire may have been tarnished, so to make sure it wasn’t I could of used some glass paper and smoved off the wire.

I could have used a totally different variable, which would change my results completely.

Overall I feel that my results were as accurate as I could have made them with the equipment I had available to me.

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