During any physical process there is usually some kind of friction, in a wire that is carrying electricity (free electrons, which are electrons that are on the outer shell of an atom and can therefore move) there is also friction but it is called resistance (opposes the current). There are four main factors that affect resistance in a wire (affect the movement of the free electrons) these are temperature, composition, cross sectional area and length. Conduction is the opposite of resistance which means as one increases the other decreases and the other way around.
Composition – The movement of the electrons in the wire (electricity) is affected by composition because if there were more free electrons then the wire would conduct better and therefore the resistance would be lower. This is because if the distance between the metal atoms is larger it is more difficult for the electrons to move from one atom to another meaning that it can’t conduct as well and the greater the resistance. Temperature – To transfer the energy from atom to atom the electrons move from atom to atom.
If the temperature is increased then the atoms will vibrate faster and it is more difficult for the electrons to move from one atom to another, that means conduction decreases and resistance increases. Cross sectional area – If the wire is wider then there is going to be more electrons per mm which means there is more ‘charge carriers’ per mm therefore meaning that it will conduct better. If the wire is conducting better then therefore the resistance must be decreasing. So essentially if you increase the cross sectional area then you are decreasing the resistance.
If we double the cross sectional area of a wire then there would be twice as many free electrons per mm consequently the wire would conducts twice as well. If it is conducting twice as well then that would mean that the Resistance is halved. This means that Resistance is inversely proportional to length R 1 l Length – If the electrons are pushed along the wire twice as far therefore the work that is done will be twice as much (because Wd = F x d). This means that if the work done is twice as much then the journey will be twice as difficult (because more force is needed) therefore meaning the resistance is doubled.
The resistance is consequently directly proportional to length R l The graph will be a straight line through the origin because the resistance and length are directly proportional (As one goes up the other goes up by the same amount). 0 Method – I will set up a circuit as shown in the circuit diagram below. In parallel to the voltage meter I will place a length of wire 1m long that I will measure with a meter rule accurate to the nearest mm. The wire will be secured with crocodile clips to make sure that it is kept in place to ensure that the circuit functions as it should do.
I will chose a low current, which will be measured on an Amp meter that is accurate to 0. 02A. I will record the length of the wire, the current (Amps) and the Voltage (Volts). This will allow me to work out the Resistance by using the equation R = V . I Then I will gently pull the wire through the crocodile clips (gently so as not to stretch the wire to a different diameter) and stop at 10 cm intervals to again measure the current and voltage. Once I have completed this for one current which will stay constant throughout I will then change the current (so that it is still fairly low) and repeat the process.
I will repeat the process with a different current and/or different diameters so that the conclusions that I make are confirmed and were not just a coincidence for one current/diameter. To ensure maximum accuracy I will repeat the process of changing the length for both of the currents and take an average of the two sets of results for each. This improves accuracy because it helps eliminate unusually high or low results that could come about because of human error.