• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17
  18. 18
    18
  19. 19
    19
  20. 20
    20
  21. 21
    21
  22. 22
    22
  23. 23
    23
  24. 24
    24
  25. 25
    25

Characteristics of Ohmic and non-Ohmic Conductors.

Extracts from this document...

Introduction

Characteristics of Ohmic and non-Ohmic Conductors

Some atoms contain loosely attached electrons. These electrons can be made to move easily from one atom to another. When these electrons move freely along a path, a current of electricity is created. Electrons can only flow freely in materials that conduct electricity. A Conductor of electricity is a substance that allows electricity to flow through it. Substances that do not conduct electricity are knows as Insulators. All metals are good conductors because inside them they have a large number of free electrons that can move easily from atom to atom. Insulators do not have free electrons inside them. Current is the flow of free electrons through a conductor in one particular direction. Current is also calculated by the amount of charges transferred per second. For current to flow, we need a cell to exert a force and provide energy. The Current flowing in a circuit depends on the cells ability to give energy. Voltage is the energy given by the cell per charge. Another factor that affects current is Resistance. As electrons pass through the conductor they encounter collisions with atoms or ions. Electrons lose their energy and the atoms gain. The atoms vibrate with more amplitude for a while, till it emits the extra energy as heat. The 1862, George Ohm discovered that the current flowing through a metal wire is proportional to the potential difference across it (provided the temperature remains constant). However this law does not apply to all conductors, due to resistance of a wire. Thus, conductors can be divided into Ohmic and Non-Ohmic conductors. In non-ohmic conductors current is not always proportional to voltage. Sometimes, when voltage increases current decreases.

...read more.

Middle

0.5

0.15

0.15

0.15

3.33

0.6

0.18

0.18

0.18

3.33

0.7

0.20

0.20

0.20

3.50

0.8

0.26

0.23

0.25

3.27

0.9

0.29

0.26

0.28

3.27

1.0

0.30

0.30

0.30

3.33

Mean Resistance: 3.29 ohms

Gradient = Current

                  Voltage

Gradient = 0.3

Resistance = 1/0.3 = 3.33 ohms

Nichrome

Length: 80cm

Width: 0.45mm

Voltage

Current (Amps)

Resistance

(volts)

Increase

Decrease

Average

(ohms)

0.1

0.02

0.02

0.02

5.00

0.2

0.03

0.03

0.03

6.67

0.3

0.05

0.05

0.05

6.00

0.4

0.06

0.07

0.06

6.40

0.5

0.08

0.08

0.08

6.25

0.6

0.10

0.10

0.10

6.00

0.7

0.12

0.12

0.12

5.83

0.8

0.14

0.13

0.14

5.93

0.9

0.15

0.15

0.15

6.00

1.0

0.17

0.17

0.17

5.88

Mean Resistance: 6.00 ohms

Gradient = Current

                      Voltage

Gradient= 0.167

Resistance= 1/0.167 = 5.98 ohms

Filament Lamp

Voltage

Current (m Amps)

Resistance

(volts)

Increase

Decrease

Average

(ohms)

0.1

6.6

6.6

6.6

15.2

0.2

9.4

9.0

9.2

21.7

0.3

10.8

10.6

10.7

28.0

0.4

12.1

12.1

12.1

33.1

0.5

13.5

13.5

13.5

37.0

0.6

14.7

14.7

14.7

40.8

0.7

16.0

15.9

16.0

43.9

0.8

17.0

17.0

17.0

47.1

0.9

18.0

18.2

18.1

49.7

1.0

19.0

19.0

19.0

52.6

Mean resistance: 36.9 ohms

Thermistor

Voltage

Current (m Amps)

Resitance

(volts)

Increase

Decrease

Average

(ohms)

0.1

10.0

9.8

9.9

10.1

0.2

17.7

17.8

17.8

11.3

0.3

25.8

26.0

25.9

11.6

0.4

34.8

35.8

35.3

11.3

0.5

44.4

44.9

44.7

11.2

0.6

53.2

55.1

54.2

11.1

0.7

64.8

67.2

66.0

10.6

0.8

78.0

80.1

79.1

10.1

0.9

89.7

93.8

91.8

9.8

1.0

107.8

107.9

107.9

9.3

Mean Resistance: 10.6 ohms

Thermistor Heating

Voltage: 1 V

Temperature

Current (mA)

Resistance (ohms)

25

12.6

67.6

30

14.8

67.6

35

16.1

62.1

40

18.8

53.2

45

21.5

46.5

50

24.2

41.3

55

27.2

36.8

60

30.8

32.5

65

34.5

29.0

70

40.7

24.6

Thermistor Cooling

Voltage: 1 V

Temperature

Current (mA)

Resistance (ohms)

70

33.8

29.6

65

31.5

31.7

60

27.9

35.8

55

25.4

39.4

50

21.5

46.5

45

19.0

52.6

40

16.9

59.2

35

15.2

65.8

30

13.3

75.2

In this section, I am going to analyze my results and draw a conclusion. From the results, I can see that Current increases with Voltage for all the graphs. But the way in which it increases is different.

Any difference in reading may be due to some error, which I will account for in evaluation.

Ohmic Conductors

...read more.

Conclusion

An LDR is a special type of resistor, which changes its resistance based on the amount light falling on it. A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. LDRs are used in electronic circuits to operate light-sensitive switches.

For this experiment, we will need:

  • Ammeter
  • Voltmeter
  • LDR
  • Filament Lamp
  • Connecting Wires
  • Crocodile clips
  • 2 Batteries

The Apparatus will be set up as shown below:

The results I expect, are shown below:

Voltage(V)

Wattage          

I will first set the Variable Resistor as at its maximum value. The variable resistor will be used to supply varying voltage to the filament lamp. Then I shall take down the readings of Voltage of the LDR at different voltages at intervals of 0.2 Vof the filament lamp.  I will take down at least 10 sets of values to investigate the varying current according to the voltage to find out the resistance in an LDR. I will take down the results in a table like the one below.

Voltage (V)

Voltage (V)

Power (Watts)

(Of Lamp)

Increase

Decrease

Average

(Of lamp)

The experiment will then be repeated, and the current will be taken, at intervals of 0.2 V, in ascending order so as to avoid errors and obtain reliable results.

Final Conclusion

Thus, from my experiments, I have found:

  • Current always increases with voltage, but the rate at which it increases varies.
  • When temperature is constant, current is proportional to voltage.
  • As voltage increases in a filament lamp, current doesn’t increase proportionally. It increases at a slower rate. Hence, filament lamps should be used with a high voltage, as they will then be brighter.
  • As voltage and temperature increases in a thermistor, current increases at a higher rate.
  • A Light dependant Resistor’s resistance varies with the amount of light falling on it.

...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. Investigating the E.m.f and Internal Resistance of 2 cells on different circuit Structures.

    The formula for finding the internal resistance if more cells are added in series is below: (x) r + (x2) ry = Ry (new value of internal resistance in new circuit) Evaluation: Main limitations of conclusion: The factors that caused inaccuracies are as below.

  2. Investigate the variation of the resistance of a thermistor with different temperatures.

    The graph shows that most points lie on, or close to, the line of best fit and therefore I can conclude that the experiment worked well as the results fitted the predicted pattern. However anomalies can be spotted in the results, for example, the first results for 35 C and

  1. Electrical Properties of a Filament Lamp - Does a Filament Lamp Obey Ohm's Law?

    And as Ohm's law says, 'this is only true when the temperature is kept constant'. The scientific reason that heat affects the resistance is in the electons. The lamp's atoms vibrate violently when heated. The electrons meet the atoms, they hit them and lose some of their energy because the atoms knock them with a lot of force.

  2. Physics - Resistivity

    preliminary experiment, you can see that there may be some inaccuracies; an example of this is that the trend of the resistance of my bulb should decrease as I decrease my EMF in my power pack, but as you can see when my EMF is at its lowest, the resistance increases slightly.

  1. Investigate the relationship between temperature and resistance in a thermistor.

    I will light the Bunsen burner and when the temperature reaches 250C will read the current through the thermistor and the voltage across it and record them. I will do this at each 50C interval up to 1000C. I will repeat the whole experiment three times to achieve the most accurate results I can.

  2. resistivity if a nichrome wire

    Repeat the experiment and this time change the voltmeter to 20cm. 9. Repeat this process up till 100cm. 10. Record the readings on the voltmeter and the ammeter (this will be constant) on a table. A partial diagram of the practical set up. (Fig 1) Circuit diagram (Fig 2)

  1. Experiments with a thermistor

    When the temperature reads 0oc, record the voltage reading, making sure that the thermistor is completely immersed in the melting ice. * Allow the temperature to increase to 10oc, and record the voltmeter reading. * Repeat the experiment to obtain two sets of values of temperature and their corresponding average voltage, and calculate its average.

  2. Investigation into how the resistance of a thermistor varies with temperature.

    10.9 31� 1.6 3.1 4.6 4.4 9.2 13.9 36� 1.6 3.0 4.5 5.1 10.0 15.7 41� 1.5 3.1 4.7 6.0 12.3 18.4 46� 1.5 3.1 4.3 6.2 12.8 18.3 51� 1.5 3.1 4.5 7.6 15.6 23.0 56� 1.5 2.9 4.5 8.4 15.9 25.5 61� 1.5 3.1 4.5 9.3 19.0 28.3

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