Explain me how infrared are detected by televison sets which are sent by remote and how does the channel change?
A remote is an electronic device which sends infra red signals whenever you press a buton on the remote controller. Each button press is translated into a sequence of 0s and 1s and accordingly the IR signal is produced.
You might have noticed the LED at the front end of the remote. The IR light cannot be seen through naked eye, but it can be seen through a mobile camera because the camera is sensitive to IR light too.
The infrared sensor of your TV receives the signal and decodes it into digital signal and sends it to the microprocessor. Appropriate actions (changing the channel, increasing the volume etc) are triggered by the microprocessor. For each operation there is a separate didital code (produced by different buttons on the remote)