Q. 314.0( 1 Vote )

A small piece of cesium metal (ϕ = 1.9 eV) is kept at a distance of 20 cm from a large metal plate having a charge density of 1.0 × 10–9 C m–2 on the surface facing the cesium piece. A monochromatic light of wavelength 400 nm is incident on the cesium piece. Find the minimum and the maximum kinetic energy of the photoelectrons reaching the large metal plate. Neglect any change in electric field due to the small piece of cesium present.

Answer :

Given, work function

Charge density


Distance d=20cm


Wavelength λ=400nm


We know that electric potential due to charged plate


is given by ,


where E is the electric field due to charged plate


and d is the distance between two plates




=


= 59V


Now, from Einstein’s photoelectric equation




Now putting the values of h, c, λ, Ф we get






≪≪V


Minimum kinetic energy required to reach the large


Metal =22.6eV


Next, maximum kinetic energy


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