resistance on a wire

This is R=V

                 I

        

R= Resistance of the object and this is measured in ohms. (Ω)

V= Voltage and it is measured in volts. (V)

I= Current and this is measured in amps. (A)

Task:

One of the factors which affect resistance is the length of wire the electrons have to travel through. I will investigate how changing the length of wire affects resistance.

Plan:

Apparatus Required:

• Power supply unit
• Variable Resistor
• Voltmeter
• Ammeter
• Metre stick
• Crocodile clips
• one metre of wire

Safety Requirements:

• Keep the voltage of the power supply low, so the wire doesn’t heat up and become dangerous.  If the wire is heated up it may also affect the resistance.
• Ensure the experiment is carried out in a hazard free zone, for example, keeping stools under the benches etc.

Method:

1. I will set up a series circuit using the power supply unit, the variable resistor, the ammeter and the length of wire which is 100cm long.
2. I will connect the voltmeter across the 100cm length of wire.
3. I will adjust the variable resistor until the electrical current is 1 A on the ammeter.
4. I will read the voltmeter to record the voltage.
5. I will then use the equation R=V/I to calculate the resistance when the wire is 100cm long.
6. I will repeat these steps when the wire is 80cm, 60 cm, 40cm and 20cm long.

Variables

For this experiment, my independent variable (what I am going to change) will be the length of the wire.  The lengths which I am going to use will be 20cm, 40cm, 60cm, 80cm and 100cm.  

The dependent variable changes as a result of the independent variable changing.  It is the one I am going to measure.  In this case, I will be measuring the voltage (using a voltmeter connected in parallel across the wire) and the current (using an ammeter connected in series).  I will be using these measurements to calculate the resistance of the wire.

The controlled variables are what will be the same throughout the experiment.  They ensure that the experiment is a fair test.  The controlled variables here will be the temperature, the cross-sectional area of the wire, the material which the wire is made out of, and the voltage of the power pack used.

Prediction:

I predict that as I increase the length of wire the resistance will also increase as the electrons have to travel a further distance and there is a greater chance of collisions.

Blank Table (example)

Results:

I repeated the experiment 3 times and here are my results.

To work out the resistance I divided the voltage by the current.

I also took the average resistance.

I then made some scatter graphs to show my data.

I put a trend line onto each of my graphs.

 

I also did a scatter graph to show the average resistance versus the length.

The graphs show that as the length of wire increases the resistance increases as well.

All my results are very close and they all agree with this theory of resistance increasing with length of wire.

These results agree with my prediction. The electrons have to travel further and have more collisions so the further they travel the higher the resistance is.

If an electrician was wiring an extension to a house I would advise him to use the shortest possible route because of; I squared R.

The longer the wire is the more resistance will be and your electrical bills will be higher because more power is required to drive the same amperage.

Evaluation:

Because of the similarity between all my experiment repeats I think I can make a firm conclusion about the effect of length on resistance.

My method worked well because my results came out right and the way I had predicted they would.

To improve my experiment I would have more thoroughly checked the wire for kinks as kinks in the wire affect the length.

Possible errors.

There are some errors which could have occurred during my experiment.

Length

Error=+/-1mm

Total error=2mm

% error= Total Area____ x 100= 2_ x100  

               Average length             500      

                                                                 =4%

Voltage

Error in voltage=+/-0.005

Total Error in current = 0.01

Average Voltage measured =2V

% Error in voltage=0.01x100=0.5%

                                2

Current

Error in current = +/-0.0005

Total Error in Current = 0.01

Average current = 1.OA

%Error in current = 0.01 x 100

                                  1

                                                   =1%

Although there are no faults or errors in my trend line, meaning that these errors are probably not present in my data, they must still be accounted for when I am analyzing results.  In my repeat I could have divided by half a percent because there is a point like 0.5% above the line