A monochromatic beam of light of wavelength 600nm is incident on a double–slit arrangement having slit separation d=0.30mm. The interference pattern is observed on a screen kept at a distance D=1.5m from the slits. Exactly at the position of the central bright fringe a clean zinc plate (work function ϕ=4.3eV) is mounted so that the light also falls normally on the plate.
(i) Calculate the fringe width produced on the screen.
(ii) Determine whether the incident light is capable of ejecting photoelectrons from the zinc plate. Support your answer with calculation of the maximum kinetic energy (if any).
(iii) The wavelength of the light is now reduced to one-half of its original value while the photon flux (number of photons per second) reaching the slits is kept the same.
(1) Find the new fringe width.
(2) Calculate the new stopping potential required to stop the most energetic photoelectrons emitted from the zinc plate.
(3) Explain qualitatively why the visibility of the interference fringes is expected to remain unchanged in this modified situation.
a. (i) –
b. (ii) –
c. (iii)(1) –
d. (iii)(2) –
e. (iii)(3) –