Download - lphsyics k
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Light Dependent Resistors
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Aim of the investigation
• Aim: To study the effect of intensity of light on a LDR ( and derive a relation )
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The principle
• A LDR is a light controlled variable resistor. It’s made of a high resistance semi –conductor of Cadmium Sulhpide. Its electrical resistance depends upon the intensity of light on the surface of the LDR.
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Apparatus
• 1. Ammeter/Multimeter
• 2. Cell/Battery
• 3. A LDR
• 4. Bulbs of varying power
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Procedure
• 1. Keep the LDR in a dark room and measure its dark resistance.
• 2. Adjust the LDR in such a way in front of the source of light falls it receives the light normally.
• 3. Keep the light source of constant power at varying distances and measure the current passing through the resistor
• 4. Keep the distance constant, and use bulbs of varying power. Measure the current for each case
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Circuit Diagram
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Distance v/s Current
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(Distance)^2 v/s Current
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Distance v/s Resistance
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• Result: From the variation of Resistance with distance, it is observed that the resistance of the LDR increases with an increase in distance
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• Real life aplications: can be found in many consumer items such as camera light meters, street lights, clock radios, night lights, outdoor clocks