How variables effect the Resistance of a Wire.

How variables effect the Resistance of a Wire

My aim is to explain how current flows through a wire and also to explain how different things can effect the resistance. I will be collecting data to see the resistance when the length or diameter of a wire is changed.

An electric current is made up of thousands of electrons passing through a wire. Everything is made up of tiny particles. Some of these particles are called electrons and can move when there is an electrical current. The more electrons that are flowing, the larger the current. Current is measured in Amperes (or Amps) this is shown as A.

As electrons flow through a wire they pump into atoms in the wire. Electrons only flow when given electrical energy. Energy is often given through an electrical cell or battery. If the cell is a complete circuit the electrons are pushed out of one end of the cell round the circuit to the other end. The size of the push is called the potential difference or voltage. The bigger the pd the bigger the current that will flow around the circuit. Voltage is measured in Volts (V).

Resistance is how difficult it is for current to flow through something. Different variables effect the resistance for example the length and thickness of a wire. Materials that have particles, which are close together, have less resistance such as copper, air has a very high resistance. High resistance gives off heat.

The Computer Test-

I am going to show how variables effect current flowing through a wire by setting up a experiment. I will use different lengths of wire that are the same thickness (or swag) and apply a current to them. I will use a ammeter to measure the current at each length and from this I can work out the resistance using Ohm’s law which is V=IxR. However, before I do this I am going to do a practice experiment on the computer. From this I can get a better idea of what my real experiment should look like. I will use a computer program, which allows me to specify particular thicknesses and lengths as well voltages and types of wire.

In my trial experiment as well as my real experiment I will use nichrome wire. Consistency is important because otherwise the findings would not be compatible.

My trial experiment shows that as the diameter of the wire decreases the resistance increases. This is what I was expecting because as the wire gets smaller there is less room for the current to flow through causing more resistance. My trial also shows as the length of the wire increases the resistance also increases. This is in line with Ohm’s Law which says V=IR, meaning if the voltage is inversely proportional to current. This happens because there is more wire, which the current has to fight ...

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In my trial I can’t control things such as room temperature, and I don’t have to think about the wire heating up because of friction like I will in the real experiment. However the computer program does give some anomalies so I must check by looking at the result tables and graph for numbers that don’t appear to match the pattern or trend.

From doing the trial test I can now see that using the length as the variable to see how it effects the resistance instead of the diameter would be more suitable because we wouldn’t have to keep changing the wire. Changing the wire is a problem because if some wire is less strait than another it would appear to have a higher resistance because it would be longer.

The Real Experiment-

Before I do my real experiment there are particular risks that I have to prevent.

The hazards are- Frayed insulation, tripping n chords and wires, running in the class room, having wet hands when working with electricity, spilling food or drink, having power supply up too high.

The risks electrocution, injuring yourself or others, falling and tripping, starting a fire.

The people who would be at risk would be me as well as those around me and the people who will use the equipment after me.

To prevent these things happening I can- check insulation isn’t frayed and no electrical wire is exposed. Make sure there is no wires or cords on the floor or where they can be grabbed or tripped on. Don, run in class, don’t eat or drink. Make sure hands are dry. I will also use basic common sense and follow all basic laboratory procedures.

If however a problem does occur, and a fire starts shout to a teacher and cover with a fire blanket. I mustn’t use water on an electrical fire. If something breaks tell the teacher and if someone is hurt then I will tell the teacher and get the nurse. After these precautions there would be no remaining risks except if there were an outside risk such as a fir in the school.

I have drawn a labelled picture of the set up of the experiment, which you will find attached. The following data is the result from the real experiment.

For the experiment I will connect a piece of nicrome wire with a swag of 26 to a meter ruler. I will connect the wire to clips connected to the power pact. The power pack will provide a voltage of 3 Amps. There will be an ammeter connected to the wire to measure current. I need to know the current so I can use V=IxR to work out the resistance. I will take 5 readings at each length to insure data collected is accurate and I can see a trend and delete anomalies if the occur. I will measure in 10cm intervals so we can see a pattern. It would be harder to see a pattern otherwise. If we did it at larger intervals (eg. 20cms) there wouldn’t be enough room on the ruler to carry out as many different lengths as possible. For example, with 10cm intervals we can measure 10 different lengths but with 20cm intervals we could only measure 5. We use nicrome because there is a large stock available and it is the same as the one I used in the trial test on the computer so we are able to compare. We use 3 volts because if it was any higher the wire would start getting hot and would cause more resistance the longer it was turned on.

In my real experiment I must make sure all my testing is fair. If it isn’t fair my result may be incorrect. To make sure my test is fair I must:

Check outside temperature- If temperature is hot when you do one experiment but cold when you do another it is an unfair test because the particles in the first would move fast while the particles in the latter would move slowly. To prevent this from happening I will check the temperature is the same and if there is more than 5˚C difference I will not carry out the experiment. I don’t think this will be a major problem as temperature is usually kept at a constant using central heating.

Materials used- Some materials have a higher resistance than others for example nicrome has a much higher resistance than copper which means that electricity finds it harder to pass through nicrome than copper. Some materials have a high resistance due to the arrangement of particles, they are not packed neatly in rows (compound metals are like this). Some metals have a high resistance because they have a high particle density.

Length- This is a variable which does effect the resistance greatly because the longer the wire the longer the wire the further the electricity needs to travel the more particles the current has to flow through. I will be using the length as my variable and will be changing it on purpose to find out how changing the length effects the resistance.

Diameter- The larger the diameter of the wire the more room there is for the current to move through. If the diameter is really small there isn’t much room for the electrons to move through so there is a high resistance. I will measure the diameter each time to make sure it is the same for all my experiments.

Obviously I may still get anomalies but if I do I will not use them in my work because it may make my findings incorrect. I can tell if I have an anomaly by seeing if it is roughly in line with the patter that is forming from my other readings. I will record all my data in tables using Excel on the computer so they can be easily entered and stored as well as read.

Prediction-

I think the results will be very similar to the ones we obtained on the computer. I think as I increase the length the resistance will increase also because the longer the wire is the more particles there is that the current has to fight its way through. This means there is more resistance. As the length increases the current will decrease because the current has further to travel.

I will measure to 2 decimal places to obtain a greater accuracy but any more detail is so small it isn’t relevant.

Readings-

Results-

I can see that the current is inversely proportional to the resistance and as the current decrease the resistance increases. The length and the resistance are proportional because as one increase so does the other. The average current ranges from 1.76 to 0.25 amps wile the resistance ranges from 1.70 and goes to 12.00 ohms. This proves current is inversely proportional to resistance. The data also shows the longer the wire the smaller the current and the greater the resistance which is what I predicted. This happens because the longer the wire the more particles the current has to fight through means greater resistance but because the wire is a long way for the current to travel, the current decreases as the wire gets longer.

Evaluation-

I can see from my readings that as the length of the wire increases the resistance increases. For example, at 10cm the resistance is 1.70 Ohms, while at 100cm is had gone up to 12.000 Ohms. I think my data is accurate because my graphs show no anomalies, there are not dots that aren’t in pattern. I also made sure all my testes were fair using the information I said earlier. If I were to do this again I would make sure I did all of the experiment on one day. I would do this because I may not have gotten the same wire and ruler as I used for the experiment the day before. This would be a problem because one wire may be more bent or curly causing the wire to be longer than is seams. This would make my data more reliable and be more accurate. I think for the purpose of my experiment that I did enough trials and can be sure that my information is correct. However if I were studying for important information at a University level or even a college level then a lot more than five trials would be needed to obtain sufficient evidence. I could have tried my experiment on different days to insure unusual circumstances that I have no control over didn’t effect my results. Another way in which I could go about investigating how variables effect the resistance of a wire is to change the diameter or temperature of the wire while applying an electric current. As you change the diameter the resistance would increase with the thinner the wire becomes because there would be less room for the current to flow through. As the wire becomes hotter I think the resistance would also increase because the particles in the wire heat up and move around making it hard for the current to move through.