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LDR EXAMINATION ANSWERS

V. Ryan © 2005 - 2009

 

A pupil has designed and manufactured a model based on the automatic control of street lights. When the light level drops the street light comes on automatically .The systems diagram below shows how the pupilís circuit works. The sensor detects when the day light fades and a relay circuit turns on the street lights.

   
The circuit below has been manufactured as a sensor. It has been developed to sense a drop in the light level.
   

1. Name of component A:   Preset or Variable Resistor

 

2. Name of component B Light Dependent Resistor (LDR)

 

3. Which component is the one that behaves as a sensor.

       Light Dependent Resistor (LDR)

 

4. How does the resistance of this component change when the light fades.

   AS LIGHT FADES ITS RESISTANCE INCREASES

 

5. Which component is used to adjust the sensitivity of the circuit.

  THE PRESET RESISTOR

   

 

   
6. The dark sensing circuit shown above can be altered to detect light. Complete the next circuit by adding the light sensor.
   

   
7. What is the name of component C shown in the sensing circuit above?
 
Name of component C:  DIODE
   
8. What is its function ?
The diode will be placed in parallel to the relay and the opposite way round. When the circuit is turned off the diode will protect the other components from back emf.
   
 
   
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