A monochormatic point source radiating wavelength `6000Å` with power `2` vate an aperture
Channel: Doubtnut
Date: 2020-07-05

A monochormatic point source radiating wavelength `6000Å` with power `2` vate an aperture A of diameeter `0.1 m` and a lorge screen SC are placed as shown in fig, A photoemissive detector D of surface area `0.5 cm^(2)` is placed at the centre of the screen . The efficiency of the detector for the photoelectron generation per incident photon is `0.9` img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/JMA_MP_C17_131_Q01.png" width="80%" (a) Calculate the photon flat at the centre of the screen and the photocurrwect in the detector. (b) If the concave lens L of focal length `0.6` m is inserted in the aperture as shown . find the new values of photon flot and  photocurrect Assume a  uniform average transmission of `80%` from the lens . (c ) If the work function of the photoemissive surface is `1eV` . calculate the values of the stopping potential in the two cases (within and with the lelens in the epertuire).