Introduction: Resistance is the ratio of the potential difference (or voltage) across a conductor to the electrical current. This formula displays this and shows how to work out the resistance: R=V / I Resistance=Voltage / Current Resistance is measured in Ohms (symbol O) as the resistance between two points on a conductor with a constant one-volt potential difference that in turn creates a current.
It is named after Georg Simon Ohm , a German Physicist between the years 1787-1854, who also created Ohm’s Law in which a metal conductor that if at a constant temperature its value(resistance) stays the same regardless the current but the value will rise if the temperature rises. A resistor can be used in a circuit that is an electrical device that opposes electrical current flow. Electricity can only flow through materials called conductors, such as copper, as their electrons are free to move within the wires to create a current.
However Insulators can not carry electricity as their electrons are held tightly inside their atoms. In a circuit there is a conventional current of electron flow from the negative terminal to the positive terminal as the diagram below shows: Inside a wire an electrons flow involves the atoms bumping into the side of the wire on its journey this slows the current down and however much the wire hinders the current in this way is the resistance and wires can vary in their resistivity according to different variables. Variables: Variables that affect the resistance of a wire are:
Length of wire The longer the wire the more resistance the current will encounter-longer distance so electrons will bump into the sides of the wire more often slowing it down. Material of wire Materials have different textures that can affect the electron flow i. e. a courser texture the more likely the electrons will get caught up slowing the current. Thickness/area of wire The thickness/area of wire can affect the resistance, as it can be a thick wire and larger area so electrons have to travel further slowing the current and vice versa. Temperature.
Temperature is a variable as it can determine how much energy there is for the electrons to run on i. e. more heat = more energy for the electrons so will move quicker making the current go faster. I will investigate how the length of the wire affects it’s own resistance. The length of a wire has a great affect on the resistance because the distance the current has to flow can determine how fast the current can go through the circuit. The length of a wire can be controlled easily and to find out how it affects the resistance it needs to be changed and the other variables to be kept the same.
Prediction: I predict that the shorter the length the less the resistance and the longer the length the more the resistance. I have predicted this as the longer the wire is the more resistance it has so the length of the wire is proportional to the resistance of the wire and if the wire is short the resistance will be small. Apparatus: BatteryVariable resistor Ammeter Wire Voltmeter Crocodile clips Method: Set up apparatus as shown in the diagram above. ^ Measure length of wire and record. Turn on power and adjust to the preferred voltage – 7. 0V.
To make this experiment a fair test I will make sure: The Voltage stays the same. The same power is used. The temperature stays the same The material stays the same The thickness/X-Area of the material stays the same. It is tested for the same amount of time. Safety: To ensure safety in my experiment I will: Keep the power low. Turn the power off when changing the measurement of the wire. Keep away from the plug and other electrical connections in the circuit.