Photo electric cell
Photo electric cell
It is an electronic device which converts light energy into electrical energy. It works on the principle of photo electric effect.
Construction
It consists of a glass tube, two electrodes - cathode & anode. Cathode is concave in shape & coated with photosensitive material. Cathode is connected to negative terminal & Anode is connected to the positive terminal of the battery.
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Working
When a light ray of suitable frequency is incident on the concave surface of the cathode, it emits electrons. These photo-electrons are attracted by the anode & flow through external circuit which produces photo electric current. This current is measured using micro ammeter (mA) connected in series with anode. When Intensity of light increases, photo electrons increases & hence photo electric current increases.
Applications
i) Automatic switching of street light
ii) Used in burglar alarm.
iii) Automatic traffic signal control.
iv) Automatic operation of water taps.
v) Automatic doors.
vi) Note counting machine.
vii) Used in recording and reproduction of sound in film earlier.
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