I predict that when the length of the wire is increased the resistance over the wire will also increase and when the length of the wire is decreased the resistance will also decrease. I have also predicted that when the wire that is tested is too small the wire will glow and/or melt and break the wire.
Equipment I will need:
Power Supply- output of 2V
Ammeter
Voltmeter
100cm of Nichrome wire (an alloy of Nickel of chrome)
Meter Ruler
Two Crocodile Clips
The factors, which must stay constant in this experiment to make it fair, are the output voltage from the power supply, which should remain the same throughout measuring. When there is not load on the power supply the voltage will rise until the power is being used when connected to the circuit. The surrounding temperature should not rise or lower too much but that is mostly out of our control. The only factor that should change in this experiment is the length of the wire, but this can only be measured as accurately as about half a millimetre by using the meter ruler.
Method
First I will measure out just over 100cm of Nichrome wire and tape the ends of the Nichrome wire to the ends of a meter ruler and make sure that it is tight across the length of the ruler. I will then connect the Voltmeter across the length of the wire in parallel and the amp meter in series in the circuit as shown in my diagram. These two instruments are used to work out the resistance across the wire when the results are being taken. To work out the resistance we would use the equation:
Resistance (ohm) = Potential Difference (volts) ÷ Current (ampere)
After the equipment is set up you would start the experiment. Due to safety we are not to use any length below 30cms as the wire melts/ burns. This is because when the voltage is put through any length of wire the same amount of heat is let out of the wire. Whether it is 5cm or 1000cm, but when the wire is smaller the heat is given out over a small space and is concentrated unlike it being spread over a large distance. This then gives out a lot of heat in a small space and that heat is enough to melt the wire and break the connection.
Diagram
This is a diagram of the experiment that I used in this experiment. There are three different measurements that you must record. One is the length of the conductor being tested (Cm) the reading on the amp meter, connected in series,(A) and the reading from the volt meter, connected in parallel, (V). By using these three measurements you can work out the resistance through the Nichrome wire and how it relates to the length of the wire.
To make the experiment fair the nichrome wire was made as tight as possible to avoid slightly shorter or longer lengths, ie to reduce the opportunity for error in our results. Also changes of temperature in the room that can be help by turning on a heater or opening the door were avoided in order to get accurate results.
Results
The graph shows good correlation and I cant find any results that stick out as being an error (outlier). By including a line of best fit onto my graph I cant predict results that weren’t recorded in the original experiment. With this red line I can predict a rough estimate of the resistance through a wire measuring 20cm, I would predict that it would have a resistance of about 4 ohms.
In figure 1.2 it shows that when the length of the wire was increased so did the resistance over the wire which is what I predicted. The reason why the resistance increases over distance is because the free flowing electrons in the wire have a higher chance of colliding with each other if they are travelling over longer distances. When the free flowing electrons collide, some of the energy they carry is lost in heat. This loss in energy is what heats the wire and sometimes, enough will melt the wire. When the electrons hit each other they loose energy in heat.
Preliminary work was conducted to see what lengths of wire should be used. We found that using a wire that was too long was impractical and so a shorter wire, up to 1meter was to be used. We found that using a length less than 30cm made the wire quite hot and so we did not test any wire less than 30cm.
