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Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 15
Q: 51. The work function for caesium atom is Calculate
(a) The threshold wavelength and
(b) The threshold frequency of the radiation
If the caesium element is irradiated with a wavelength 500 nm, calculate the kinetic energy and the velocity of the ejected photoelectron.
Answer: This is given that the work function
(a) From the expression, , we get:
Where,
Substituting the values in the given expression of
Hence, the threshold wavelength is 653 nm.
(b) From the expression, we get:
Where,
= threshold frequency
H = Planck՚s constant
Substituting the values in the given expression of:
Hence, the threshold frequency of radiation
(c) According to the question:
Wavelength used in irradiation
Kinetic energy
Kinetic energy of the ejected photoelectron
Since K. E
Hence, the velocity of the ejected photoelectron (v) is