• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The aim of this investigation is to find out if the length of an electrical resistor (graphite putty) affects its resistance.

Extracts from this document...

Introduction

Physics Coursework: Electrical Resistance

Aim:

The aim of this investigation is to find out if the length of an electrical resistor (graphite putty) affects its resistance.

Prediction:

An electrical current is the movement of electrons through a substance. Resistance occurs when the electrons travelling through the substance collide with the atoms of the substance. This collision slows down the flow of electrons causing resistance. Resistance is the measurement of how hard it is for electrons to move through a substance. The resistance of a substance is measured in Ohms (Ω), which can be shown in the formula:

        Voltage

        Resistance = ---------------          (Equation 1)

        Current

All substances have a resistance, the more resistance a substance has the less current gets through. The resistance of a substance can be altered by factors which include:

  • Temperature

Heat energy gives the atoms of the resistor more energy causing them to vibrate. This results in more collisions between the passing electrons and the atoms of the resistor. Therefore, resistance of a resistor is increased if the temperature is increased.

  • Cross-sectional area

The larger the cross-sectional area is, the less likely the electrons will collide with the atoms of the substance they are flowing through. Therefore, resistance of a resistor is decreased if the cross-sectional area is increased.

  • Length

The electrons have to travel a longer distance if the length of the resistor is increased. More collisions will occur between the electrons and the atoms of the substance. Therefore, an increase in length results in an increase in resistance.

I predict that a longer resistor will give higher resistance.

...read more.

Middle

3.5

0.88

3

0.04

0.0004

3

3.5

1.17

2

0.04

0.0004

2

3.5

1.75

1

0.04

0.0004

1

3.5

3.50

Method:

As stated in the plan, except that we did not have time to repeat Method 2 three times.

Safety:

The following are the steps we took to make the investigation safe:

  • We used a low voltage to reduce risk of electrocution.
  • We did not touch any exposed wires when the power was on.
  • We were careful when we cut a segment from the graphite putty.
  • We cut the graphite putty on a cutting tile.

Fair Test:

The following are the steps we took to ensure that the investigation was fair:

  • We used the same graphite putty for every experiment.
  • The width and height of the graphite putty remained constant (width = 2cm, height = 2cm), only the length changed.
  • We used the same voltage in every experiment.
  • We cleaned the surface of the copper plates to remove any impurities or oxides that may alter our results.
  • We covered the whole of the cross sectional area of the graphite putty with the copper plates.
  • We performed the experiment in an air-conditioned environment; therefore the temperature was constant.
  • We allowed the graphite putty to cool down after each experiment, to prevent an increase in resistance after the current passed through it.

Results and Analysis:

Table 2 in the next page summarizes the results of Method 1 where currents passing through the resistor were measured. For each length, we have included the three individual readings, the calculated average of the three readings, the predicted result as derived in Table 1, and the percent deviation comparing our experimental result to the prediction.

With a quick glance, we notice that the first two experimental results are inconsistent to the rest of the other results. While the rest of the currents we recorded increase as the length of the graphite putty decrease, the current recorded for the length of 14cm was slightly lower than that for the length of 15cm.

Graph 2 illustrates the effect of the length of resistor on the current passing through it. The black line shows the average current obtained from our measurements against the length of the resistor while the red line represents the predicted relationship between the current and the length of the resistor. Both graphs produce upward curves showing an exponential increase in current as the length of the graphite putty decreases. This is because current is inversely proportional to the length of the resistor.

Table 2: Results of Method 1

Length of resistor (cm)

Current (A)

% deviation

1st reading

2nd reading

3rd reading

Average

Predicted

15

0.23

0.23

0.22

0.23

0.23

-3

14

0.22

0.22

0.22

0.22

0.25

-12

13

0.24

0.23

0.23

0.23

0.27

-13

12

0.29

0.27

0.26

0.27

0.29

-6

11

0.30

0.30

0.30

0.30

0.32

-6

10

0.36

0.36

0.35

0.36

0.35

2

9

0.39

0.39

0.39

0.39

0.39

0

8

0.44

0.43

0.43

0.43

0.44

-1

7

0.55

0.55

0.55

0.55

0.50

10

6

0.64

0.63

0.62

0.63

0.58

8

5

0.70

0.75

0.73

0.73

0.70

4

4

0.90

0.89

0.88

0.89

0.88

2

3

1.10

1.07

1.16

1.11

1.17

-5

2

1.40

1.39

1.48

1.42

1.75

-19

1

1.98

2.01

1.98

1.99

3.50

-43

...read more.

Conclusion

Another reason of error in a longer resistor could be that heat energy produced is higher since the resistor is longer and electrons flowing through it collide with more atoms. This heat energy causes the atoms to vibrate more vigorous thus increase the resistivity of the graphite putty and give rise to errors. If I were to repeat this experiment again, I would monitor the temperature of the graphite putty because a change in temperature would change the resistivity of the substance. I would monitor the temperature with a thermometer and only perform the experiment when the graphite putty is at a certain temperature so that the resistivity is the same.

To improve the experiment, I would use acid to clean the surface of the copper plates because this would remove all impurities and oxides from the surface of the copper plates. Using sandpaper to clean the surface of the copper may not have removed all of the impurities. These impurities and oxides may have increased the resistance slightly.

Conclusion:

The results I obtained are accurate enough for me to make the conclusion that the length of a resistor does affect the resistance of the resistor. An increase in length of the resistor results in an increase in resistance because there are more atoms for the electrons to collide with. This supports my original prediction that the resistance will increase if the length of the resistor increases. Furthermore, resistance of a resistor is directly proportional to its length. Doubling the length doubles the resistance because there are twice as many atoms; so there are twice as many collisions. Halving the length would halve the number of atoms in the resistor resulting in half the number of collisions; therefore resistance is halved.

By Tsun-Kidd Wong, 11JI

                Page  of

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Peer reviewed

    Measurement of the resistivity of Nichrome

    5 star(s)

    So I calculate the standard deviation of the values I got for the diameter. The standard deviation of a collection of numbers is a measure of the dispersion of the numbers from their mean value. If many data points are close to the mean, then the standard deviation is small;

  2. Peer reviewed

    Investgating resistivity - Planning and Implementing

    4 star(s)

    Given the electricity involved, the experiment should be kept away from water, or other liquid conductors. Hypothesis Each value of R obtained from a certain length will be equal within the limits of experimental error. When R is plotted against l, the line of best fit will be a straight line through the origin, demonstrating direct proportion.

  1. Investigate how the temperature affects the resistance of a thermistor.

    negative number and as this is impossible I would assume that from that point the resistance would be 0? if the temperature went any higher. Another possibility is that I would not reach a point of no resistance but instead level out at a resistance slightly above that because it

  2. The aim of my investigation is to determine the specific heat capacity of aluminium.

    I therefore recorded the values of time to the nearest second. * First I added extra lagging to my aluminium block making sure that the top of the heating filament and thermometer hole is covered to prevent heat loss. * Connect circuit as shown in the diagram above.

  1. Physics - Resistivity

    in the bulb, so I can draw a table, find the averages, and draw a graph; this would ensure I get as much of an accurate result a possible and minimise any affects that errors would have on my result.

  2. Internal resistance investigation - I will conduct the following investigation with the aim to ...

    Interpretation: From my results I have used the average of each measurement to construct a graph of voltage against current (see graph) I have drawn a line of best fit and believe from the look of the graph and from the background information I collected earlier that it is a straight line.

  1. Measuring The Resistivity Of A Pencil Lead.

    error of ?3.5% * In calculating the averages with a percentage error of ?3.5% Anomalies My main anomaly is at length 145mm as the pencil lead snapped not allowing me to take any readings for that length. My other set of anomalies is at 125mm-135mm.

  2. Does the length of a conduction putty affect its resistance?

    am investigating is an Ohmic conductor, as even when the potential difference changes, the resistance of the putty remains constant for the same length. Now that I have proved that the putty does conduct electricity in a constant manner, I can start the main experiment.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work