Question

what is the phenomena of photocell..??

Answer 1

When light of frequency greater than the threshold frequency of the cathode material falls on the cathode, photoelectrons are emitted. These electrons are collected by the anode and an electric

 current starts flowing in the external circuit. The current increases with the increase in the intensity of light. The current would stop, if the light does not fall on the cathode. 

USES OF PHOTOCELL

  A photocell can be used in any situation where beam of light falling on it is interrupted or broken by any mean.  To count vehicles passing a road.  To count items running on a conveyer belt. To open doors automatically in a building such as banks or other commercial buildings or offices.  To operate burglar alarms.  To produce sound in movies.