MAKING A LIGHT SENSETIVE SWITCH

This project is based on the phenomenon of photoelectric effect. When a matchstick  is lit and its light (or any light) falls on the photo detector or LDR, the electric circuit gets completed and as a result the electric bulb starts giving out light.

You Require
6 volts D.C. battery.
One table lamp or torch bulb holder fitted with 6-volt bulb
One LDR or photo detector
One transistor 2N 1177
50 kilo-ohm potentiometer
One switch
One plastic sheet

What To Do
•    Take a plastic sheet and connect all the components as shown in the figure.
•    Connect two terminals of the table lamp with the circuit as shown in the figure.
•    Cover the photo detector or LDR with a metal cap so that no outside light falls on it.
•    When you wish to demonstrate the switching on of the bulb, make the switch on and lit the matchstick and bring it near the LDR or photo detector. The bulb will start glowing.
•    As long as the light from the bulb of the table lamp is falling on the detector, the circuit will remain on, when you wish to put-off the bulb you have to put-off the main switch of the circuit.