Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 15

Q: 51. The work function for caesium atom is Equation 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 Equation

(a) From the expression, Equation , we get:

Equation

Where,

Equation

Equation

Equation

Substituting the values in the given expression of Equation

Equation

Equation

Hence, the threshold wavelength Equation is 653 nm.

(b) From the expression, Equation we get:

Equation

Where,

Equation =threshold frequency

H = Planck’s constant

Substituting the values in the given expression of:

Equation

Equation

Equation

Hence, the threshold frequency of radiation Equation

(c) According to the question:

Wavelength used in irradiation Equation

Kinetic energy Equation

Equation

Equation

Equation

Equation

Equation

Kinetic energy of the ejected photoelectron Equation

Since K.E Equation

Equation

Equation

Equation

Hence, the velocity of the ejected photoelectron (v) is Equation

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