• 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

physics sensor coursework

Extracts from this document...

Introduction

Physics coursework – sensor circuits

In this investigation, I will be constructing a circuit which involves a sensor. I will calibrate this circuit and then test it in an environment outside the laboratory.

The sensor I have chosen to use is a light dependant resistor, LDR. From my preliminary research, I found that this sensor works by changing its resistance as light levels are modified. This change is not proportional though, but a curve as shown:

image00.png

image01.png

The resistance changes because the LDR is made up of a semi conducting material. When more photons hit the LDR, more electrons break free to act as charge carriers, thus reducing resistance in material.

Circuit

I shall incorporate the LDR into a potential divider circuit, in an arrangement called a “Wheatstone Bridge”. An advantage of the Wheatstone Bridge, which is described in the “AS Advancing Physics” textbook, is that it only detects changes in the ratio of the two pairs of resistors. This means that an amplifier would only increase the changes in voltage output, rather than the whole thing. Also, the circuit would be unaffected by any outside changes – such as temperature – as the variable would cause the same proportional effect to each resistor. This means the ratio of each pair of resistors remains constant, so same output voltage.

Above is the preliminary design of my circuit. Terminal A is connected to the positive; whilst terminal B is connected to the negative. It works because an increase in light intensity causes the LDR’s resistance to drop. This drop in resistance means there is less potential at terminal A in the circuit. Potential at terminal B stays the same as the resistors are fixed. The potential difference across the two terminals is measured.

...read more.

Middle

267.36

800

4.35

18.67

232.99

900

3.89

18.73

207.69

1000

3.73

18.85

197.88

Set 2:

Light intensity/ lux

Potential difference/ V

Current/ mA

Resistance/ ohms

0

13.21

1.11

11 900.90

100

9.76

7.69

1269.18

200

7.97

12.65

630.04

300

7.26

13.27

547.10

400

6.73

16.34

411.87

500

5.99

17.51

342.09

600

5.28

18.05

292.52

700

4.83

18.25

264.66

800

4.32

18.72

230.77

900

3.98

18.77

212.04

1000

3.61

18.97

190.30

Set 3:

Light intensity/ lux

Potential difference/ V

Current/ mA

Resistance/ ohms

0

13.18

1.07

12 317.76

100

9.76

7.94

1229.22

200

8.02

12.58

637.52

300

7.16

13.22

541.60

400

6.75

16.44

410.58

500

5.92

17.32

341.80

600

5.23

18.06

289.59

700

5.02

18.33

273.87

800

4.14

18.92

218.82

900

4.16

18.78

221.51

1000

3.70

18.64

198.50

Set 1:

image05.png

image06.png

Set 2:

image07.png

image08.png

Set 3:

image09.pngimage10.png

Averaged set:

Light intensity/ lux

Potential difference/ V

Current/ mA

Resistance/ ohms

0

13.19

1.08

12 212.96

100

9.78

7.77

1258.69

200

7.99

12.60

634.13

300

7.22

13.26

544.49

400

6.73

16.38

410.87

500

5.96

17.44

341.74

600

5.25

18.06

290.70

700

4.90

18.24

268.64

800

4.27

18.77

227.49

900

4.01

18.76

213.75

1000

3.68

18.82

195.54

Average V        =        (V1 + V2 + V3)/ 3

Average I        =        (I1 + I2 + I3)/ 3

Average R        =        Average V/ Average I

For example; at 0 lux:

Average V        =        (V1 + V2 + V3)/ 3

Average V        =        (13.18 + 13.21 +13.18)/ 3

Average V        =        13.19 V

Average I        =        (I1 + I2 + I3)/ 3

Average I        =        [(1.06 + 1.11 +1.07) ×10^-3]/ 3

Average I        =        1.08×10^-3 A

Average R        =        Average V/ Average I

Average R        =        13.19/ 1.08×10^-3

Average R        =        12 212.96 Ω

image11.png

There is a degree of error in graph shown all graphs, but error displayed in graph below is due to averaging and to some extent, the resolution of measuring equipment (e.g. voltmeter reads to 2 decimal places).

Resolution of voltmeter = 0.01 V

Error in measurement if reading is constant = ±0.005 V

Max value        =        Max V/ Min I

Min value        =        Min V/ Max I

Max error min        =        (Error at lowest value/ Lowest value) ×100

Max error max        =        (Error at highest value/ Highest value) ×100

At 0 lux:

Max value        =        Max V/ Min I

Max value        =        (13.21 + 0.005)/ [(1.06 – 0.005) ×10^-3]

Max value        =        12 526.07 Ω

Min value        =        Min V/ Max I

Min value        =        (13.18 – 0.005)/ [(1.11 + 0.005) ×10^-3]

Min value        =        11 816.14 Ω

Error max        =        (313.11/ 12 526.07) ×100

Error max        =        2.50%

Error min        =        (396.82/ 11816.14) ×100

Error min        =        3.36%

At 100 lux:

Max value        =        Max V/ Min I

Max value        =        (9.82 + 0.005)/ [(7.68 – 0.005) ×10^-3]

Max value        =        1280.13 Ω

Min value        =        Min V/ Max I

Min value        =        (9.76 – 0.005)/ [(7.94 + 0.005) ×10^-3]

Min value        =        1227.82 Ω

Error max        =        (21.44/ 1280.13) ×100

Error max        =        1.67%

Error min        =        (30.87/ 1227.82) ×100

Error min        =        2.51%

At 200 lux:

Max value        =        Max V/ Min I

Max value        =        (8.02 + 0.005)/ [(12.57 – 0.005) ×10^-3]

Max value        =        638.68 Ω

Min value        =        Min V/ Max I

Min value        =        (7.97 – 0.005)/ [(12.65 + 0.005) ×10^-3]

Min value        =        629.40 Ω

Error max        =        (4.55/ 638.68) ×100

Error max        =        0.71%

Error min        =        (4.73/ 629.40) ×100

Error min        =        0.75%

At 300 lux:

Max value        =        Max V/ Min I

Max value        =        (7.26 + 0.005)/ [(13.22 – 0.005) ×10^-3]

Max value        =        549.75 Ω

Min value        =        Min V/ Max I

Min value        =        (7.16 – 0.005)/ [(13.29 + 0.005) ×10^-3]

Min value        =        538.17 Ω

Error max        =        (5.26/ 549.75) ×100

Error max        =        0.96%

Error min        =        (6.32/ 538.17) ×100

Error min        =        1.17%

At 400 lux:

Max value        =        Max V/ Min I

Max value        =        (6.75 + 0.005)/ [(16.34 – 0.005) ×10^-3]

Max value        =        413.53 Ω

Min value        =        Min V/ Max I

Min value        =        (6.71 – 0.005)/ [(16.44 + 0.005) ×10^-3]

...read more.

Conclusion

     Also, the temperature of the LDR and the resistor should be constantly monitored. Current passing through a component with any resistance will result in heat being produced. Therefore, if the voltage setting on the power supply was too high, the resistors may overheat, which can lead to a fire.

My proposed new method:

  1. Set up sensor circuit.
  2. Turn off all the lights in the dark room.
  3. Set 23˚C on the thermostat, and leave the room at that temperature for 5 minutes.
  4. Connect up the lamp and set the power supply to 10V.
  5. Measure the light intensity beside LDR using a light meter.
  6. If light intensity is above desired value, move the lamp away from the sensor; but if the light intensity is below desired value, then move the lamp towards the sensor.
  7. Continue steps (ii.) and (iii.) until required value of light intensity is achieved.
  8. Record the voltage output.
  9. Turn power supply off for a minute, so the circuit can cool down.
  10. Repeat the procedure for other values of light intensity.
  11. Using the equation, V = IR, work out the resistance of the LDR.
  12. Plot a graph of light intensity against resistance.
  13. Plot a graph of log light intensity against log resistance.
  14. Derive a formula linking the two variables using y = kxn.
  15. Test the formula in a minimum of six different locations.

Bibliography

Source

Information

http://www.tiscali.co.uk/reference/ encyclopaedia/hutchinson/m0030304.html

LDR is a semi conductor, made out of a material such as cadmium sulphide.

http://en.wikipedia.org/wiki/Photocell

LDR conducts electricity via positive holes and negative electrons.

http://www.electroflash.org.nz/schoolh/symbolsall.htm

The symbol for an LDR.

http://www.technologystudent.com/elec1/ldr1.htm

Resistance falls rapidly from 0 lux to 100 lux.

http://www.gcsescience.com/pe27.htm

Graph of light intensity against resistance for an LDR.

AS Advancing Physics – Edited by Jon Ogborn and Mary Whitehouse

The advantages of using a Wheatstone bridge over a normal circuit.

...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)

    There are several possible sources of error and uncertainty in the experiment. 1. The most likely error might be reading the ammeter and voltmeter. As the voltage and current are always changing, it is hard to read precisely.

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

    Safety aspects considered: There are some aspects which need to be considered when carrying out this investigation. The first aspect is that the resistors can become too hot as the experiment goes on, therefore the resistors should be approached and handled with care to avoid minor burns.

  1. Measuring The Resistivity Of A Pencil Lead.

    Due to this I feel that that's why there is not much off a spread in my raw data results. The results I have collected are the ones I would have expected. Using a current of 0.1A allows me just to move the decimal place to the right thus I

  2. Physics - Resistivity

    Current across bulb (I) Resistance of bulb (V/I) 12 10 1.51 6.62 12 9 1.43 6.29 12 8 1.34 5.97 12 7 1.25 5.60 12 6 1.16 5.17 12 5 1.05 4.76 12 4 0.94 4.26 12 3 0.81 3.70 12 2 0.68 2.94 12 1 0.52 1.92 12 0 0 ?

  1. Characteristics of Ohmic and Non Ohmic Conductors.

    This leaves a hole in the atom and it becomes positively charged. Once this happens it is capable of attracting an electron from another atom and the electron from this atom. So now this hole moves from atom to atom and as this happens, the electrons also move from atom

  2. The aim of the experiment is to verify the maximum power theorem and investigate ...

    Results & Calculations Number of blocks 1 2 3 4 Applied force (F) Static friction (fL) 1.0 N 2.6 N 4.4 N 6.2 N Kinetic friction (fk) 0.8 N 2.4 N 3.2 N 4.8 N Normal Force (R) 1.94 N 3.883 N 5.835 N 7.811 N In the following calculations, we have made several assumptions: 1.

  1. Making, Calibrating and Testing a Sensor

    However a fixed resistor will be used, that would have selected in my first experiment. Then as opposed to testing only light and dark, the sensitivity will be tested from a distance of 30cm back using a piece of card to replicate the car and a lamp to replicate the

  2. Light intensity notes

    The Doppler Shift ?out and ?back are fairly self explanatory, and obviously ?back > ?out if the object is moving away, and the opposite if it is not. This differs from the method used with the asteroid as continuous waves rather than pulses are used.

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