The work function of a photoelectric material is 4.0 eV.

(a) What is the threshold wavelength?


(b) Find the wavelength of light for which the stopping potential is 2.5 V.


(a) Given, work function W0 (Ф) =4 eV

We know that, W0=hf=hc/λ


is the threshold wavelength,


h is Planck’s constant,


c is the speed of light,


⇒


⇒



(b) Given, stopping potential, Vstop = 2.5V


∴ From photoelectric equation, hf =Kmax +Ф


⇒


Where Ф is the work function,


is the wavelength of light,


h is Planck’s constant,


c is the speed of light,


e is the charge on electron,


is the stopping potential


⇒


⇒


⇒



1