Physics Plan - Resistance of a Wire Aim The aim of my investigation is to investigate how length affects the resistance of a wire. Theory The four factors that affect the resistance of a wire are: o Length o Material o Temperature o Cross section Resistance is the force, which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. Resistance is measured in ohms. Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance.

Resistance is a measure of how hard it is to move the electrons through the wire. Length: The larger the length of the wire, the larger the resistance. This is because there are more atoms from the metal so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance Temperature: When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigour sly because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway. This increases the amount of collisions therefore there is more resistance.

Material: Different materials have different resistances because the materials' atomic structures are different so some metals have low resistances and some have high resistances. The type of material will affect the amount of free electrons that are able to flow through the wire. The number of free electrons depends on the amount of electrons in the outer shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase of the number of electrons. If the particles in the material are tightly packed together, the electrons will have more collisions and therefore more resistance.

Ohm's Law: resistance = potential difference in volts / current in amperes V = I/R I will use this formula to work out the resistance of the wire Prediction I predict that if the length increases then the resistance will also increase in proportional to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Therefore, if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. If the length of the wire is only half the length of the wire on the same type of wire, there should be half the number of collisions between the electrons and the atoms. If the wire is twice as long, there should be twice the number of atoms, resulting in twice as many collisions and a predicted doubling of the resistance.

Diagram Method o Set up the circuit as above o Record ammeter and voltmeter readings - do this three times to get an average o Change the length of the wire, each time you do this measure the current and voltage, repeat three times for an average Fairness To make this investigation a fair test I am going to keep factors constant which are: o Power supply on same power each time o Surrounding temperature must be the same o Equipment should be the same o The edges of the crocodile clips should be at the end of the measured length of the wire Safety o Handle the power supply carefully o Be careful when touching the wire - it might be hot o Be careful when cutting the wire to change the length o Make sure the mains to the power supply is switched off when removing the wire from the circuit to be measured Results Table Length (cm) Current (amps) Voltage (volts) Resistance (ohms) V = I/R 1 2 3 Av 1 2 3 Av.