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The aim of my investigation is to investigate how the brightness (intensity) of light shining on the LDR (Light Dependant Resistor) affects the Resistance.

Extracts from this document...

Introduction

Planning

The aim of my investigation is to investigate how the brightness (intensity) of light shining on the LDR (Light Dependant Resistor) affects the Resistance.

We can change the intensity using different methods. One method is to increase the voltage, by plugging the power supply to a higher voltage. But this method can be hard as you might not be able to know how higher the voltage is, it might be harder to have access to higher voltage, as it is dangerous.

Another way is to change the brightness by adjusting the power supply. Also the distance between the bulb and the LDR is another method, if the distance is bigger, the less bright it would be. If the distance is less/smaller, the denser it will be.

We could also use different bulbs and power supply, with a higher voltage and energy, the higher the voltage, the brighter the light bulb. But this may be hard, as we might not have many different power supplies or bulbs. I could also put different densities of filter between the bulb and LDR. The last method that I could use is to use different sizes of the apertures used in the experiment. If an aperture is more open, then more light will flow through, but if the aperture is more closed then light will hardly pass through.

Middle

The thing with Inverse Square Law is that if the distance doubles, the inverse intensity will be ¼. If the distance is 3 times more, then the inverse intensity will be 1/9th of the light, because of the distance being

Method

First of all using an ammeter, a voltmeter, a LDR, a bulb and battery; the circuit was built.

I made sure that the power supply was set on 12.

Then I switched on the power supply to see if the bulb and the battery are working.

After that, I accurately measured the distances on a piece of paper. The paper was a great help because it showed me exactly where my LDR should be placed.

At last the lights were turned off and we could start our experiment. The external light was still entering the room through windows for safety reasons. Without external light, a person can’t see where he is going and might bump into someone, damaging equipment and may be hurting themselves especially when handling with glass (bulb).

Then the LDR was placed in position and the power supply was switched on.

I noted down the result, and continued to do so for the rest of the readings. I took the experiment twice for every reading as there were two trial used for the accuracy of results.

Conclusion

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Voltage (V)

Current average

Current (Amps)

Resistance (ohms)

Trial1      Trial2

(milliamps)

4cm

36           37

1.5V

36.50

0.0365

41.10

16cm

30           29

1.5V

29.50

0.0295

50.85

36cm

22           21

1.5V

21.50

0.0215

69.77

64cm

17           16

1.5V

16.50

0.0165

90.91

100cm

14           14

1.5V

14.0

0.0140

107.14

As I will be using the ‘Inverse Law Square’ rule for my graph,

I have also included the actual plotted distance.

In order for the ‘Inverse Square Law’ to work, I have squared

the distances.

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

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