Resistance of a wire.

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Philip Jacobs 11R

Resistance of A Wire

Theory and Background Write Up

Wires have resistance because they have thousands of atoms inside them. When voltage flows through a wire the electrons hit these thousands of atoms. This slows down the electrons. This slowing down process is what we call resistance. The electrons always travel from negative to positive on diagrams, although in conventional current it actually flows in the other direction.

Figure 1 – Inside of a Wire

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The resistance of a wire can be altered depending on the following: -

  • The material of a wire – This can be because some wires have more atoms inside them than others do.
  • The temperature of the wire – If there is a high temperature in the wire then the atoms will vibrate more. This means that electrons are more likely to “hit” the atoms.
  • The cross-sectional area of the wire – When the cross-sectional area of a wire increases the resistance of a wire goes down. This is because the area that is occupied by atoms is reduced.
  • The length of a wire – When the length of a wire is increased so is the resistance of that wire. This is because there are more atoms inside a longer wire.

The factor that I have chosen to investigate is how the length of a wire effects the resistance of the wire. I have chosen to investigate this factor because I have only one type of wire available to use in the experiment. That wire is called constanton. If I were to increase the temperature of the wire I would have no piece of apparatus available to accurately measure the temperature. Finally I have no piece of apparatus to accurately measure the cross sectional-area of a wire and I am limited to the cross-sectional areas of wire that I have available to me. When doing my main experiment I am going to keep the voltage in the circuit the same. I am also going to keep the temperature as constant as I can. In all the experiments that I do I am going to keep the type of wire and the thickness of the wire the same.

Ohm’s law states that current is directionally proportional to the voltage applied to a conductor and inversely proportional to the conductors resistance.

Source –  

This will help me in my investigation because it will help me in working out the resistance of the wire using the following formula: -

                                        

                                                Or

Preliminary Investigation

When I conducted my preliminary investigation I did it so that I could test and check that the currents and voltages that I would use in my main investigation.

Preliminary Investigation Write Up

Apparatus

In my preliminary investigation I used 70cm of constanton wire, 3 crocodile clips, 6 coated wires, 1 power pack, 1 ammeter, 1 voltmeter, 1 meter ruler, 8 pieces of cellotape (3cm each) and 1 pair of scissors.

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Method

  1. I plugged in a power pack to a plug socket and connected a wire to it. I put this wire in to my ammeter.
  2. Out of this ammeter came another wire on the end of this wire was a crocodile clip which I attached to the constanton wire which had been attached to the meter ruler.
  3. Connected to this crocodile clip was another crocodile clip which via another wire led to a voltmeter which was in parallel to the meter ruler.
  4. Coming out of the other side of the voltmeter was another wire. Again ...

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