Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 16

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Q: 52. Following results are observed when sodium metal is irradiated with different wavelengths. Calculate

(a) Threshold wavelength and,

(b) Planck’s constant

Threshold wavelength and planks constant

(A) Assuming the threshold wavelength to be , the kinetic energy of the radiation is given as:

Three different equalities can be formed by the given value as:





Dividing equation (3) equation (1):

Note: part (b) of the question is not done due to the incorrect values of velocity given in the question.

Q: 53. The ejection of the photoelectron from the silver metal in the photoelectric effect experiment can be stopped by applying the voltage of V when the radiation is used. Calculate the work function for silver metal.


From the principle of conservation of energy, the energy of an incident photon (E) is equal to the sum of the work function of radiation and its kinetic energy (K.E) i.e.,

Energy of incident photon (E)


C=velocity of radiation

h=Planck’s constant

Wavelength of radiation

Substituting the values in the given expression of E:

The potential applies to silver metal changes to kinetic energy (K.E) of the photoelectron. Hence,