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# Resistance of a Wire

Free essay example:

Janice Valentinus        Yr 10 GCSE        Physics Coursework

Resistance of a Wire Coursework

Planing (Final)

Independent variable:

-Length of wire (cm)

Dependent variable;

-Dial voltage (4 volts)

-Material of wire (Nickel chrome)

-Width of wire (28 SWG)

Aim:

My aim is to see how the length of the wire affects the resistance.

Prediction & Hypothesis:

My prediction is that when the length of wire increases, the resistance will also increase. Same as when the length of the wire doubles, the resistance will also doubles because Resistance is caused when the electrons collide with the ions. Therefore when it is doubled, the electrons will collide with twice as many ions, so the resistance will also double.

Introduction:

Measuring equipments

I have chosen a digital voltmeter and an ammeter as my measuring equipments because it shows the voltage and current in decimal points, so I know that my results can be more accurate.

Range and intervals

My length of wire will increase 10 cm every time and I will make 6 readings. I will repeat all my reading twice and get the average to make sure that they are the most accurate results that I can get.

Results Plan

The heading for my results table will be ‘dial voltage’, ‘actual voltage’, ‘length of wire’, ‘current’, and ‘resistance’. To ensure a fair test I will make sure that the dependent variable will be the same through out the experiment.

Safety

I will assure that when I conduct my experiment, I will have a clear space between me and other students. I will use a heat proof mat to be the base of the wires so it will not heat up. The dial volt will be 4 and I will not have the length of wire shorter than 10 cm so the wire will not heat up.

ApparatusMy Circuit Diagram -Power supply (1)

-Digital voltmeter (1)

-Digital ammeter (1)

-Crocodile clips (2)

-Nickel chrome wire (60cm)

-Connecting cables (5)

-Scissors (1)

-Ruler (1)

-Heat proof mat

Apparatus Set-Up Diagram Method:

1. Set up the apparatus as shown above.
2. Measure and cut the wire according to your measurements.
3. Connect the wire to the crocodile clips.
4. Turn on the power supply to 4 volts.
5. Record the volts and currents for each time you change the wire.
6. Repeat experiment two more times.

Obtaining Evidence

To get the resistance: V/I = R

Table of Results

(1)

 Dial Voltage(volts) Actual Voltage (volts) Length of Wire (cm) Current (amps) Resistance (ohms) 4 2.40 10 2.30 1.04 4 2.72 20 1.66 1.64 4 3.26 30 0.95 3.43 4 3.10 40 0.80 3.88 4 3.10 50 0.53 5.85 4 3.19 60 0.60 5.32

(2)

 Dial Voltage(volts) Actual Voltage(volts) Length of Wire (cm) Current (amps) Resistance (ohms) 4 2.59 10 2.12 1.22 4 2.90 20 1.34 2.16 4 3.07 30 0.95 3.23 4 3.14 40 0.73 4.30 4 3.23 50 0.61 5.30 4 3.20 60 0.50 6.4

(3)

 Dial Voltage(volts) Actual Voltage (volts) Length of Wire (cm) Current (amps) Resistance (ohms) 4 2.72 10 1.64 1.66 4 2.74 20 1.02 2.69 4 2.90 30 0.75 3.87 4 3.02 40 0.70 4.31 4 3.10 50 0.58 5.34 4 3.15 60 0.51 6.18

Analysis & Conclusion

Final average result:

This is my average resistance from my three results:

To get the average: Add up the resistance from the three experiment and divide it by three (the mean average of the resistance).

 Resistance (ohms) 1.31 2.16 3.51 4.16 5.50 5.97

Observation:

My results agreed with some of my hypothesis. As shown on my graph, as x (the length of the wire) increases, y (the resistance) also increases. But when x doubles, y does not double. Take a look at an example from my data:

10 cm = 1.31 Ω

20 cm = 2.16 Ω

When I double the length, the resistance did not double. I think this is because of some factors that can affect the resistance of the wire that are not controlled.

1. Thickness of the wire

Even though I know that for the experiments I did, I always use the nickel chrome wire 28 SWG, it was not a fair test if some of the wire are thicker than the other in some sides. I did not measure the thickness of the wire, therefore this factor can tell us why the results does not fully agree with the hypothesis.

2. Temperature of the wire

When I did my experiment, I did not control the temperature of the wires at all. Temperature affects the resistance of a wire because temperature affects the vibration of atoms and molecules in the wire. When the temperature increases, the vibration increase and can cause the free electrons to collide. This electron carries electrical currents, so the resistance can change due to the temperature.

3. Other things

The experiment can also be affected by the resistance in the connective cables, or maybe the crocodile clips are not functioning properly and not in place. I might not also coil the wire to the clip accurately the same through out all my experiments.

So I think this is why some of my results do not fully agree with my hypothesis. If I have controlled these factors from the beginning, I could get the most reliable result.

My graph shows a positive correlation and the increase of the resistance is almost constant. I think that my results can be more accurate next time by controlling the factors above.

Evaluation and improvements:

I can improve my experiment next time by controlling all the factors that affect my results. To control the temperature, I can use a temperature-controlled water bath so the temperature of all experiment is kept the same all the way. This can determine the reliability of my results. I can also make sure that the wires are all properly straightened out, have the correct measurements and the same width. I can make sure that the wire are coiled properly to the clips and have the same rotations of coil through out my experiment. My experiment can also be improved by making sure that the connective cables are in the same length, width and diameter so that the resistance are the same.

Conclusions:

I think that my experiment went pretty well, and my results are also positive. At first I just had slight problems trying to design the circuit. It was really hard to get the circuit working especially when the ammeter wouldn’t work. But I managed to get it working and managed to repeat the experiment three times.

If I could do the experiment again next time, I would try and control all the variables I stated in my observation to get a more accurate and reliable result.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.  ## Here's what a star student thought of this essay

4 star(s)

### Response to the question

The student has answered the set question of "how the length of the wire affects the resistance" very well, making a table and a graph, using these to manage to determine that as the length of wire increases, so does ...

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### Response to the question

The student has answered the set question of "how the length of the wire affects the resistance" very well, making a table and a graph, using these to manage to determine that as the length of wire increases, so does the resistance and giving an explanation as to why. I would recommend however that the student could of went a bit further in answering the question by working out an equation as to how length affects resistance. When plotting the graph, the student should of arranged the resistance on the y axis and length on the x axis (as he did), as the independent variable ( the one they change) should go on the x axis.

However after they did this they would get a straight line graph which means that y is proportional to x, or that y=x multiplied by a constant. Or y=kx. To work out this constant they could of calculated the gradient by doing the change in y divided by the change in x (y1-y2/x1-x2) be careful to make sure that the value for x1 is taken from the same co-ordinate as the value as y1. And the same for x2 and y2, you could easily slip up here. Make sure to take the gradient over a large distance, e.g. if y goes from 0-10, make sure y1 is at least around 8, and y2 around 2. Forming an equation from his results would add a little more depth to the work.

### Level of analysis

The student shows good practical skills, clearly laying out safety and drawing a circuit diagram before they start the experiment. Always draw a clear circuit diagram first as it will stop you from being confused when setting up the experiment. The student also has laid out exactly what they are going to do before they do it, which will again stop you from tripping up. The student recognises that you can not directly measure resistance and has used Ohm's law appropriately to calculate resistance. The student has also recognised where the largest errors in his method and has noted them down and how they could of reduced these errors a good way to make sure you learn from your mistakes, however I would recommend before starting an experiment to think where the largest errors will occur and how you could reduce them.

### Quality of writing

I would recommend always checking over your work at the end as you can make silly mistakes. There are no real technical mistakes in the students work, however there are many grammar and spelling mistakes which would of easily been noticed had they checked over (e.g. "have" instead of "had"). However this is clearly not a big deal in science coursework. I would of recommended however that the student instead of drawing four graphs they could of saved a lot of time by just putting columns repeat 1, 2, 3, average into one table underneath a measurement that is repeated and put all repeats and average in one table.

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Reviewed by jackhli 09/02/2012

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