Experiment to discover how factors affect resistance in wire

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Experiment to discover how factors affect resistance in wire

Aim

To investigate how the length of wire affects its resistance.

Hypothesis

I predict that as the length of wire increases, the resistance will also increase. This is because current is the flow of electrons in a circuit and voltage is the push which makes the electrons flow through the circuit. Resistance is caused by components in circuits which slow the flow of electrons down as it is harder for them to flow through the circuit. There is resistance in wire and as the electrons have further to travel through longer lengths of wire they face more resistance, therefore the longer a piece of wire is, the higher the resistance will be. The greater the resistance, the more voltage is needed to push a current through the wire. The resistance of a wire is calculated by the formula Resistance = Voltage/Current, which is known as Ohm’s law.

Plan

An experiment will be carried out in order to discover how factors affect resistance. Therefore variables that can affect resistance must be considered: they include temperature, voltage, current, the length of the wire, the diameter of the wire and what type of metal the wire is made of. The resistance of the wire will be calculated by taking the readings of the voltage and current through the wire for each result. Each set of results will be recorded on a Voltage/Current graph and the gradient will be used to discover the resistance of the wire, as the temperature is constant (on the graphs) and will therefore not affect the results. There will be two independent variables: the length of the wire and a variable resistor, used to alter the voltage across the wire. Length is the chosen independent variable because it is easier to measure accurately than diameter. Length of wire is easier to alter than it is to find wires of the same length and diameter but of different materials. Temperature throughout the wire would be difficult to measure accurately and varying the length is safer than voltage because if a short piece of wire was used with a high voltage, it would melt. The dependent variable that is calculated will be the resistance, and this will be calculated by measuring the voltage and current of the wire, at different lengths. For each length of wire the voltage (the second independent variable) will also vary and the current will be measured at each voltage using an ammeter. Readings of the results will be taken using a voltmeter and an ammeter. A preliminary experiment will be carried out to determine the number of results taken in the actual experiment.

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In the preliminary experiment, equipment was set up using a power pack, a metre of wire, attached to other wires using crocodile clips, and a variable resistor. A voltmeter and an ammeter were also in the circuit to measure the results.

Preliminary results:

From the preliminary experiment it was decided that the readings will be taken at 8 different lengths, each 10cm apart, ranging from 30cm to 1m. The variable resistor will also change the voltage through the wire 7 times at each length.

Equipment:

  • Power pack
  • Ammeter
  • Voltmeter
  • Variable resistor (rheostat)
  • Masking tape
  • ...

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