Class 11 Chemistry Structure of Atom Planck’s quantum theory

Planck’s quantum theory:

According to this theory:

  1. Energy emitted or absorbed is not continuous, but is in the form of packets called quanta .In terms of light it is called as photon.
  2. Each photon carries an energy which is directly proportional to the frequency of wavelength i.e. E depends upon v (nu).
    1. Or E=hv (where v is frequency)
    2. Value of h =6.634 x 10-34Jsec
  3. Energy associated with no of packets is given by:

E=nhv (where n is an integral multiple)

This formula can also be written as:

E = (nhc)/ (λ)

 (Because we know frequency=speed of light/wavelength)

V = (c/ λ)

EXPLANATION OF BLACK BODY AND PHOTOELECTRIC EFFECT ON THE BASIS OF QUANTUM THEORY.

For the ejection, minimum frequency is required called threshold frequency .Let’s say light that falls, has energy equal to hv .Out of this h , a amount of h  is used as binding energy and rest is given to electron as kinetic energy.

Mathematically

Class_11_Chemistry_Structure_Of_Atom_Planck'sConstant_1

Following observations were made

  1. If frequency is greater than threshold frequency: Than ejection occurs and also, kinetic energy is imparted to ejected electron.
  2. If frequency is equal to threshold frequency, than only ejection occurs.
  3. If frequency is less than threshold frequency, than no ejection occurs and no kinetic energy is imparted.

Please note hvo is called as wave function.

Black body radiation

When light falls on the surface, the particles gain energy and starts oscillating. When more energy is supplied the oscillations increase, amplitude increase .Therefore, the colours keep on changing.

Problem 1:

  1.  Calculate the energy of a mole of photons of radiation whose frequency is 5 x 1014 Hz?

Answer 1:- 

Class_11_Chemistry_Structure_Of_Atom_Answer_6

  1. A 100-watt bulb emits monochromatic light of wave length 400 nm. Calculate the  number of photons emitted per second by the bulb.

Answer 1:-

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