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Investigate the effect the thickness of wire has on it's resistance.

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Rosie Higgins                                19/11/01



Aim: To investigate the effect the thickness of wire has on it’s resistance.


Nickel Chrome Wire cut into 10 pieces of 30cm length (Ruler, Pliers)

Two crocodile clips

Five Pieces of Wire

Power Source

Variable Resistor


Volt Meter


  • The Circuit was set up as in the circuit diagram overleaf with a power source of 5 Volts, an ammeter, crocodile clips (holding wires), and a variable resistor in series and a Voltmeter in parallel with the wires.
  • Nickel chrome wire was then measured to discover the cross section width with a micrometer screw gauge and this was recorded and the cross sectional areas was calculated using πr² multiplied each time by the number of wires used, each bit of wire was cut into lengths of 30 cm
  • The crocodile clips held one piece of nickel chrome wire of thickness 34 mm and length 30 cm at the same point on the ends of the wire.
  • The power source, ammeter and voltmeter were then switched on.
  • The voltage and current for the wire were then recorded, and recorded again when the variable resistor’s slider was moved to the middle and again when the slider was moved to the end.
  • The Power was turned off while another was added to avoid overheating.
  • Another wire, or exact same properties (Nickel Chrome, thickness 34 mm and length 30cm) was placed on top of the previous wire, in the same position, both straight and flat.
  • The Power was turned on again and the same procedure was repeated, recording current and voltage at three points on the variable resistor.
  • This was repeated 10 times in all, each time, an extra wire of exact same properties (Nickel Chrome, thickness 34 mm and length 30cm) was placed on top of the previous wire in the same position, all straight and flat and the current and voltage was recorded at three points on the variable resistor.
  • The resistance was then calculated using the formula R =V/I (resistance equals voltage (v) over current (a)) for each thickness of wires, three times and
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Circuit Diagram

Measures to ensure a fair test

Certain measures were taken to ensure that the results were as accurate as possible. Therefore, the wire was kept consistent, it was always Nickel Chrome which had the presumably had the same cross section width and was cut into the same length to prevent the length affecting resistance. The same equipment was used and the same voltage (5 volts) was used for each. Therefore the only variables were the number of wires and the position on the variable resistor. The crocodile clips have to keep the wire at the same length and hold all the wire at the same point to make it a fair test.


The resistance will be lower the thicker the wire (more wires) because resistance is lower with a cross sectional surface area.

This is as, as the wire gets thicker the electrons in the wire have more room to flow, resistance will become lower and current will flow more easily. If the wire is a good conductor the resistance will be lower. The higher the resistance, the lower the current. I already know that the when the cross sectional area of the wire is increased, the resistance decreases as in a previous experiment involving a bulb, the bulb brightened when I doubled over the wire (increased the cross sectional area). I know that altering the variable resistor would vary the current and voltage. Resistance will be greater the greater the current.


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The evidence, though it gives the basic link between the thickness of wire and resistance, it is not always reliable as certain elements cannot be controlled such as room temperature which may not remain constant during the experiment (especially if, as I did the results were gathered on different days and at different times on those days) and overlooking things which may in some way alter the results. For example, the cross sectional area of the wire was just measured once and is quite likely to be inconsistent along the wire. The conclusion is likely to be correct though could be more detailed if the investigation was taken further.

There are roughly no anomalies and I have received incredibly accurate results, allowing me to form an excellent line of best fit..

To further the investigation

To further the investigation, these results could just be seen as a starting point and other variables could be changed to investigate the effects of different conditions on the resistance. Temperature (of room), length of wire, types of wire (instead of using just nickel chrome, the experiment could be repeated each time but with different wires and investigate their resistance in relation to mass or thickness), voltage etc. could all be changed to investigate the effects and they could all be recorded as the effects on resistance.

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