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Rev. Notes > IGCSE > Electric Circuits
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Electric circuit

Circuit symbols Circuit diagrams
Diode Diode as forward biased and reversed biased Diode as a rectifier
Diode as half wave rectifier Diod as full wave rectifier Transistors
Series circuits Parallel circuits Effective or equivalent resistance in series circuits
Effectice or equivalent resistance in parallel circuits Advantages of connecting lamps in parallel in lighting circuits Potential divider or Potentiometer
Thermistors Light dependent resistor - (L.D.R.) Input transducers
Capacitors Capacitance of the capacitor One Farad
Different types of capacitors Time delay circuits Relay
Rectifier circuits Transistor as switch Light sensitive switch
Temperature operated alarms

Light sensitive switch

Consider the following circuit.

The relay is not energized so long as the resistance of the LDR stays low. If the illumination reduces, the resistance of LDR increases and the potential difference across the coil goes up. When the illumination is sufficiently low, the relay will close the contact.

Note that the circuit controlled by the relay does not need to have any connection whatsoever to the relay coil circuit. This can be an important safety features of the circuit.

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View Comments on this Chapter - Total Comments (12)
O,sidds Said :
THERE SHOULD HAVE BEEN MORE DIAGRAMS!!! but the explanations are good.
  12/01/15 10:30 PM
skyler Said :
you are missing diagrams! but helpful website!
  02/05/13 03:18 AM
Bareera Khizar Said :
gr8!!! useful 4 last min revision nd especially 4 lazy lumps!!
  14/04/13 09:13 PM
Bareera Khizar Said :
gr8!!! useful 4 last min revision nd especially 4 lazy lumps!!
  14/04/13 09:13 PM
  14/10/12 06:53 PM
Lakshey Said :
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  29/08/12 08:07 AM
Thiago Said :
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  12/06/12 03:02 AM
Aubrey Graham Said :
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------------------------------------------------------------------------------------- Admin Replied:

We are glad it helped you :) keep visiting and thanks for your feedback

  22/05/12 03:23 PM
Ghost Said :
Thnak you sir, really helpful but some of the diagrams are missing, if u could post those too, it would be helpful... Safwan :)
  16/05/12 02:24 PM
Irshad Said :
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------------------------------------------------------------------------------------- Admin Replied:

Thank you :)

  17/04/12 10:37 AM
Princess Zoya Said :
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------------------------------------------------------------------------------------- Admin Replied:

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  10/04/12 03:36 PM
Coop Cooper Said :
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------------------------------------------------------------------------------------- Admin Replied:

Thank you :)

  28/03/12 10:04 PM


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