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Class 12th Physics 2018 Set1 Delhi Board Paper Solution

Question 9

If light of wavelength 412.5 nm is incident on each of the the metals given below, which ones will show photoelectric emission and why?

Metal Work Function
Na 1.92
K 2.15
Ca 3.20
Mo 4.17


A metal will show photoelectric emission in below situation:

E ≥ work funciton

Now according to the relation below:

E =   h (c/λ)

E = 1240 / λ

λ = 1240 /412.5 nm 

λ = 3.006 eV

So here, work function of k and Na are less than incident energy of photon. Hence, only potassium (k) and Sodium (Na) will show photoelectic emission.

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