Dino Sabnani Physics Coursework 20th September 03 Aim- To investigate factors affecting the resistance of a wire. There are a plenty of things I can alter which will change the resistance of a wire such as the voltage/ length of the wire, the thickness of the wire and the temperature of the wire. Most of these are quite impossible to change. However an easy one in which we can alter easily and receive accurate results would be the length of the wire. The things in which I will control will be things such as the thickness of the wire, material and voltage or current. I have picked Constantan as the wire for this investigation.

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You will see later in the preliminary work why I have chosen this material. Hypothesis- After doing some research and using some scientific knowledge. I have come to a conclusion that an increase in the length of wire is an increase in resistance. Electrons carry charge. But the charge each electron carries is extremely low. So there are millions and millions of electrons flowing through a circuit. More electrons per second mean more current. The current is calculated by . I equals current, Q is charge and T is time. When the length of the wire increases, the electrons will have to pass through more and more atoms in the wire.

More collisions will happen, this means that there will be more electrons bumping through the atoms in the wire. When the electrons bump into each other this has 2 effects, firstly it slows down the rate in which electrons can pass through, and the kinetic energy will be transformed into thermal energy. Not all of the electrons will pass through the entire peace of wire some will be left behind. The same applies when we are talking about the thickness of the wire. The thinner the wire the fewer gaps there are going to be for the electrons to pass through. This is an example of what goes on inside a wire when current is passed though-

Safety There is not much safety features involved in this experiment. However there are two things which you must not do- -Do not touch the wire it may get hot and possibly burn you. -Do not increase the voltage to much, it will increase the temperature of the wire and will turn red hot then burn. Variables / controlling the experiment The length of the wire is what I will mostly change in this experiment. This will alter resistance of the wire. When the length of the wire increases, the electrons will have to pass through more and more atoms in the wire.

More collisions will happen, this means that there will be more electrons bumping through the atoms in the wire. When the electrons bump into each other this has 2 effects, firstly it slows down the rate in which electrons can pass through, and the kinetic energy will be transformed into thermal energy. Not all of the electrons will pass through the entire peace of wire some will be left behind. This therefore means by increasing the length the resistance will also increase. I will change this variable to investigate the resistance based on the length of wire. I will keep the thickness of the wire constant for the obvious reason.

If we change the resistance of the wire the resistance will also change. This is because the thinner the wire the fewer gaps there are going to be for the electrons to pass through. The more gaps the more space there will be to allow the electrons to pass through the wire. Therefore we will keep this constant to allow a fair test. I will also try my best to keep the temperature of the wire the same. The temperature varies because when the electrons bump into the atoms, due to the friction caused in the crash of electrons, kinetic (or thermal) energy is generated.

And to a certain level, the electrical energy carried in the electrons is transferred in to kinetic energy as well. It is very hard to control the temperature. After every single experiment I will have to turn of the machine, if I leave it on it will heat up the wire which will make it an unfair test. We will also have to keep the type of wire constant. This is because by changing the type of wire we also change the density of the wire, and the amount of atoms inside the wire, which could therefore affect the resistance of the wire. Preliminary Work-

An experiment was carried out to ensure the experiment would work properly. It was set up as follows. The wires used were Nichrome with gauge of 28, 30, 32, and 36. Copper with gauge of 28, 30, 32, 36. Constantan with gauge of 28, 30, 32, 36. For each of these pieces of wire I recorded three different lengths 200cm, 100cm and 20cm. We set up the experiment as follows. Results- As we can see from the experiment our experiment will work because the current passing through each of the wire is increasing as the length of the wire is shortened.