In a photoelectric-effect experiment it is observed that no current flows unless the wavelength is less than 570 nm .
a) what is the work function of this material?
b) what is the stopping voltage required if light of wavelength 420 nm is used?

0.77842 V

Explanation:

h = Planck's constant =

c = Speed of light =

= Wavelength

Work function is given by

The work function is

Stopping voltage is given by

The stopping voltage required is 0.77842 V

(a) 3.49 x 10^-19 J

(b) 0.78 V

Explanation:

threshold wavelength, λo = 570 nm = 570 x 10^-9 m

(A) the work function of the metal is given by

where h is the Plank's constant and c be the speed of light.

h = 6.63 x 10^-34 Js

c = 3 x 10^8 m/s

Ф = 3.49 x 10^-19 J

(B) λ = 420 nm = 420 x 10^-9 m

Use Einstein relation

where, Vo is the stopping potential

eVo = 1.246 x 10^-19

Vo = 0.78 V

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