My aim is to find out what affect a length of a wire has on its resistance. The resistance will be measured by finding out the current and the voltage travailing through a wire at variable lengths.

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Investigating Resistance

By Chantelle Wright

10B

Planning

Aim

My aim is to find out what affect a length of a wire has on its resistance. The resistance will be measured by finding out the current and the voltage travailing through a wire at variable lengths. I shall use 11 different lengths of wire so that I have a good range of readings and will be able to plot a line of best-fit graph from the results. The lengths will range from 10 cm to 100 cm and will have a gap of 10 cm between each length of wire so that for example I will have one wire with a length of 10 cm and the next smallest length of wire as 20 cm. I shall measure the lengths in centimetres as I want the divisions between the results clear and I believe that it will be easier to ensure that the wire is a precise number of centimetres. I am starting at 10 cm, because any length below that may be unsafe.

Background knowledge

         Resistance is the opposition to the flow of electrons. As the electrons flow through the wire they bump into atoms. When they bump into an atom, the electron looses some energy and slows down.

         The resistance is directly proportional to the length of the wire, i.e. if you double one you double the other. Therefore, the longer the wire, the larger the resistance

I have found out what affects the resistance from the physics book “The World of Physics” by John Avison, published by Nelson on page 231 and 247. From this, I learnt that different wires may have a higher resistance because of their dimensions (length and width) and the material the wire is made from all of which effect the resistance

Hypothesis

        I think that the shortest wire (10 cm in length) will have least resistance and the longest wire (100 cm in length) will have the highest resistance. I think the resistance for the 100 cm wire will be 10 times as much as that for the 10 cm wire.

I think this because, according to “The World of Physics” by John Avison, “a long wire has a greater resistance than a short wire.” This statement can be explained when you think that if for a certain length of wire the resistance (anything that prevents the current from flowing) is a certain amount, when you double the length you also double the resistance, because there are more of the things (the edges of the wire for example) that are preventing the current of electrons from flowing as freely. The electrons will have that small-constricted amount of space to flow through but for double the distance and hence not as much current will be able to flow. Therefore I think the 100 cm wire’s resistance will be 10 times the resistance for the 10 cm wire, because that resistance is being applied for 10 times as long.  I think that my graph shape will be a straight line because as you double the length I believe the resistance will double.  

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Circuit Diagram

Equipment

         I am planning to use this equipment:

  • Two crocodile clips
  • A Ruler
  • A digital ammeter
  • A digital voltmeter
  • A variable low voltage power supply
  • A calculator
  • Connecting wires
  • 100 cm of wire
  • Micrometer screw gauge
  • Variable resistor

Fair Test

I have decided to test how the length of the wire affects the resistance of the wire and so I shall ...

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