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Explore how the resistance of a wire changes when we alter values affecting the resistance.

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Resistance Wire Investigation


In this investigation, I plan to explore how the resistance of a wire changes when we alter values affecting the resistance. These values can be one of the following:

  • Power – I am to use the same current and voltage across the battery all the time – 3V
  • Cross-sectional area (thickness) – This will be kept constant, as a change causes a big change in resistivity. I will use a micrometer screw gauge at certain intervals along the wire. The wire size is 30swg
  • Heat – Again, this affects resistance, so I will try to keep heat constant
  • Density / Wire type – I will use constantan wire. I am not going to change either of these variables, as I do not have the resources available to me.

I am to carry out the investigation considering the length of the resistance wire. This wire will be made out of constantan allow. From a preliminary test, I have decided that it would be practical to take readings every 10cm. This is because it would take too long if any more results were found, and the collaborate data would be less accurate if less readings were taken.

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In the diagram above, the variable resistor represents the resistance wire, which is made of the metal allow, constantan. Using the resistance wire, I am employing both an ammeter & a voltmeter in order to calculate the resistance along the wire using Ohm’s law.

Ohm’s law states that the potential difference is the same as the current multiplied by resistance (as long as temperature is kept as a constant) or:

V=I x R  

In order to calculate resistance you are able to change the equation to form ‘resistance  =  voltage divided by current’, or:

R=V / I

As previously stated, Ohm’s law can only be engaged when temperature is constant. As it is difficult to keep temperature constant when conducting the experiment, allowances must be made – though it is possible to calculate such heat changes.

When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway.

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I predict that when the length of a wire is increased, its resistance will also increase. I also think that the rate at which the resistance increases will be constant and directly proportional to the length. I think that I can explain this. Electric current is the movement of electrons through a conductor – a metal wire in this case. When resistance is high, conductivity is low. Metals such as constantan conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, to jump along the lines of atoms in a wire, which are in a lattice structure. Resistance is when these electrons, which flow towards the positive, collide with other atoms; they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means the resistance is doubled.
However; it may not obey Ohm’s law, due to the temperature increases in the resistance wire.

...read more.

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