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To investigate how the Resistance of a Constantan Wire is affected by its length

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Aim: To investigate how the Resistance of a Constantan Wire is affected by its length

Introduction:In this experiment we will be investigating how changing the      

length of a piece of Constantan wire will affect the resistance.  

                           Therefore the length will be an independent variable and all of  

                           the other variables we will try to keep the same. The other  

                           variables included in this experiment are temperature, thickness

                           of wire and density of wire. Resistance is a force, which

                           opposes the flow of an electric current around a circuit so that

                           energy is required to push the charged particles around the  


Key factors:

  • Thickness of the wire: if the wire is thin, the electrons are forced to travel through a smaller area, therefore colliding more frequently, resulting in them giving up more of their energy to surrounding particles.

-    Temperature: resistance of the wire increases as the temperature    

      increases, as the atoms are oscillating faster. When an electro      

      collides with an atom, it loses its energy. If the wire cools, the  

      resistance will decrease.

  • Length of Wire: the longer the wire the larger the resistance, due to the fact the electrons have a further distance to travel, increasing the possibility of any potential collisions.
  • Wire density: If the wire has a high density, the resistance will be  

Higher, as there are more atoms found in a smaller space. This leaves less, and smaller, gaps for the electrons to flow through. Because of the lack of space, we would expect there to be more collisions between the atoms and electrons.

Preliminary results:

  • The reason for doing preliminary research was to get an indication of the patterns I could expect in my results. Also, it was considered a practice, so if any errors were made in the first attempt, then they could be eradicated in my real experiment. Using these results, I can now make a prediction as to what I should expect in the real investigation.


  • Now that I have completed the experimental side of my  

Investigation, I can use the results to explain if my prediction is correct, and if not, why not.                


  • In electricity, the property that transforms electrical energy into heat energy is resistance. A common factor that the entire conductors share is the fact that they have free electrons in the outer shell of their structure. Resulting from this, in all conductive atoms the outer electrons are able to move freely, even in a solid (in this particular experiment the Constantan wire).
  • I predict that every time I decrease the length of the wire, resistance will increase accordingly. This is because the longer the conductor, the more particles there are in one way, resulting in the electrons finding it difficult to flow. Also, as the length of the wire is longer, this means electricity has further to travel, but because it is in a longer wire, collisions will be less frequent.
  • The Constantan wire is very thin: therefore there is a smaller area for electrons to travel through. On their journey from negative to positive, there are more and more collisions, giving energy to surrounding particles.
  • I know that as the resistance increases, the temperature of the wire will rise. This is due to the fact the atoms in the wire are oscillating faster. I believe the temperature of the wire is directly proportional to the length and resistance.
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100 cm ruler: to measure the wire accurately.100cm wire: to experiment upon.1 ammeter: to measure the current in the circuit.1 voltmeter: to measure the voltage in the circuit.Connecting wires: to connect all necessary apparatus to the circuit.Crocodile clips: to connect the wires to the devices.1 power pack: to supply AC current and control voltage.



  • Collect all of the equipment and set up as shown in the diagram. Make sure the ammeter is placed in series and the voltmeter inserted in parallel.
  • Set the wire to 100cm, and place two crocodile clips at the first  

      measurement, 0-10cm.

  • Record the current in amps and the voltage in volts into the results table.
  • Repeat the process from step 2, remembering that one crocodile clip should always be placed on 0cm, with the other one moving up 10cm’s each time.
  • Continue doing this until all measurements up to 100cm have been made.
  • Using results gathered work out averages of the current and voltage.
  • Using the formula R=V/I, work out the resistance in ohms with a  


Factors ensuring a fair experiment:

  • Do not alter the positions of any of the devices during  


  • Record the current and voltage accurately, using correct units.
  • Always place the crocodile clips on the exact measurement.
  • Before beginning experimentation ensure all apparatus are fully operational.
  • Leave the voltage at the same level throughout the experiment.
  • The wire must be straight as bends may affect resistance.
  • The reading of the voltage should be taken promptly as when the current passes through the wire, the wire will become hotter, but I wish for heat to not play that big a role in my results.

Safety Precautions:

  • Keep the power pack voltage below 2V.
  • Ensure all equipment is safe to use.
  • If you smell burning, quickly switch off from the mains.
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