To find out how the resistance changes as the length of the wire changes.

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Coursework: Resistance of a Wire

Aim

To find out how the resistance changes as the length of the wire changes

Equipment

  • Constantan Wire 1m
  • Power Pack – 4V
  • Digital Ammeter
  • Digital Voltmeter
  • 3 x Crocodile clips
  • 3 x Crocodile/plugs
  • Metre rule.

Variables

The independent variable is the length of the wire. This will be measured with a metre rule and the range of the length will be 10cm to 100cm increasing by 10cm each time.

The dependant variable is the resistance. The resistance will be measured by dividing the average result for the voltage by the average result for the current – Resistance = Voltage/Current

The control variables are the thickness, temperature and the type of wire.

Method

Measure three lots of the same of the same length of constantan wire

Connect up the circuit; as shown in the diagram below, ammeter in series, voltmeter in parallel to the component (wire).

Record the results for each length from the ammeter and voltmeter and take the average.

Using the results, work out the resistance - R=V/I

Make sure the power supply is switched off when not in use.

Obtaining Results

I will use my equipment to obtain my results by using the ammeter to measure the current and the voltmeter to measure the voltage. By doing this I can get a reliable result for the resistance – R=V/I

To ensure my results are accurate as possible, I will do the experiment three times for each length. By doing it this way I can take the average of all three. I will take three readings for each length from the ammeter and the voltmeter and I will then take the average of the three to divide them to get an average result for the resistance. I am doing this to get reliable results so I can see how reliable my experiment was.

I am using digital ammeters and voltmeters to get an accurate result as I will get a number to two decimal places.

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I have chosen to use constantan wire as from recent research I have found that it is not affected by heat from the outside of the wire. I have also found from doing a preliminary experiment that Constantan Wire gives a higher resistance than Nichrome Wire. I am using a thickness of 26 s.w.g because if the cross-sectional area increases, the resistance decreases but if the cross-sectional area decreases the resistance increases. This is because there is less room for the free electrons to collide and therefore friction from them creates heat and if the temperature increases, the resistance of ...

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