Investigation into how the length of a piece of wire effects its resistance

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               Investigation into how the length of a piece of wire effects its resistance

Aim

Using different lengths of constantan wire, investigate how different lengths of wire effect its resistance.

Planning

My preliminary work before the actual experiment included going on a Science computer programme, on the topic resistance of a wire. In which I used to decide upon how I was going to do my experiment. I will take readings of lengths of wire from 0-70 cm and to make these readings accurate I will do them three times and take an average.

This is what the circuit will look like:

Prediction

I predict that the longer the length of the piece of wire, the more resistance it has. So, if you double the length of the wire, the resistance would be doubled aswell. When a metal wire is put into an electrical circuit, current from the battery makes the electrons flow through the wire. In doing so, they collide with the metal ions and this slows down the flow of electrons in the circuit. So, in a longer piece of wire you would expect more metal ions, with more metal ions there you would expect there to be more electrons colliding with them. Resistance is caused by electrons colliding into ions, if the length of the wire were doubled the electrons would ‘bump’ into twice as many ions so there would be twice as much resistance. An objects resistance is a measure of how difficult it is to push a current through the object. Resistance is measured in Ohms, if you had a material with a resistance of 1 ohm, a potential difference of 1 volt will push a current of 1 Amp through it. But if you use a material with a resistance of 2 Ohms, you would need a potential difference of 2 Volts to push the same 1 Amp current through it. Mathematically, Resistance= Voltage/Current. Current is the flow of electrons moving round a circuit. Metal ions in a wire, would slow down this process as electrons collide with them. The electrons motion is impended, and less current is allowed to flow (current is halved). Effectively the resistance doubles (according to Ohms law). Ohm’s law states that the amount of current flowing in a circuit is directly proportional to the electromotive force impressed on the circuit and inversely proportional to the total resistance of the circuit. The law is usually expressed by the formula I=E/R, where I is the current in Amperes, E is the electromotive force in volts, and R is the resistance in Ohms. This enables us to work out the resistance using the current and voltage. As I expect the longer the piece of wire, the more resistance it has, I also would assume that the length of the wire is directly proportional to the resistance of the wire. This prediction is supported by the fact that the flow of electrons have a longer distance to travel and therefore collide with more metal ions and slow down because the electrons have been deflected. I would expect the graph to show a straight line through the origin, showing that length is proportional to Resistance.

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Current represents the number of electrons flowing per second. If the resistance is high; the flow of electrons is slowed down and so the number of electrons per second is reduced (i.e. the current is reduced), increasing the resistance.

Method

  1. Decide upon the different lengths of wire you want to use for the experiment
  2. Attach two wires at the positive and negative on an Ohmmeter. At the other ends of these wires attach crocodile clips.
  3. On a meter ruler, sellotape the constantan wire down across it. Attach the positive crocodile clip to the constantan ...

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