Investigation on how the resistance of a wire changes with its length

I measure the voltage and current and use Ohm's law to find out what the resistance of this piece of wire is.

What wire will I use?

I will need a wire that conducts electricity. Although copper seems like a good choice, as it is a very good conductor, it will offer very little resistance, which means the         experiment will be pointless. Instead a wire made from an alloy would be an excellent choice as it is conductive but offers resistance.

Variables

Factors that are likely to affect my investigation are:

·        The length of the wire,

·        Temperature,

·        Thickness of wire.

Since the aim of my investigation is to find out does the length of a wire affect its         resistance I will be changing the length. Temperature is a common problem as a        current flowing will also create a heat build up and this will give inaccurate results.       I will minimize this factor by only using the circuit when I need it and leaving it open     the rest of the time preventing a lot of heat building up. The heat built up will become negligible and therefore not affect my results. The thickness of the wire will be kept     constant by using the same wire each time I repeat the experiment.

Measurement

In my experiment I will take the following readings:

·        Voltage

·        Current

·        Length of wire

To measure the voltage I will use a voltmeter. This is connected in parallel with the     piece of wire like this:

I will have the voltmeter at a suitable scale so I will get accurate readings. The 10V     scale will give me accurate reading ranging from 1V-10V.

       To measure the current I will use an ammeter. An ammeter is connected in series and it is not important where it is connected unlike the voltmeter it will give the same reading everywhere in the circuit. This because current, unlike voltage is not used up by components in the circuit. I will be using lengths of wire increasing in size by 10cm every time ranging      from 10cm to 1m.

Apparatus

1. Wire (100cm) N.B. for my investigation I used nichrome 23

2. Rheostat

3. Power supply

4. Six connecting wires

5. Two crocodile clips

6. Voltmeter

7. Ammeter

8. Switch

Results

When I do the experiment I will collect the data in tables like these:

Using these tables I will be able to work out the resistance from any piece of wire and at any position on the variable resistor. For example if I wanted to find out the resistance for a 40cm piece of wire at position 2 I will take the value of current and divide it by the value of the voltage.

   After this I will draw up a second table of length and resistance. It will look like this:

I will then use the figures on the above table to draw a straight-line graph of resistance against length.

Predictions

 I think that as the length of the wire increases so to will the resistance of it. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length.

As the length of the wire is increased the number of collisions between charged          particles and fixed particles also increases and therefore the value for the resistance of the wire becomes higher.

Practical Procedure

1.Set up this circuit:

2.Connect the 10cm length of wire.

3.Use the switch to turn on the circuit and take the voltage and current values.

4.Change the position on the variable resistor and repeat step 3.

5.Repeat steps 4, five more times.

6.Go back to step 2 but use the next length of wire  (20,30,40,50,60,70,80,90,100 cm)

Safety

This experiment is not terribly dangerous but as always with any investigation you     must be careful.  Ensure that your hands are dry and check that the wires you are     using and all other equipment is in good condition before beginning the investigation

From the graph we can see a very clear pattern, as the length of the wire                      increases so does the resistance of it.  Note as well that the increase is relatively          constant. This is shown by the fact that the line drawn is a straight one.

Conclusion

         By looking at my results on both the tables and the graph I have concluded that my prediction was correct. The resistance did change in proportion to the length. This is because as the length of the wire increased the electrons that made up the current had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance.