Class 11 Chemistry Structure of Atom | Planck’s quantum theory |

__Planck’s quantum theory: __

According to this theory:

- 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.
- Each photon carries an energy which is directly proportional to the frequency of wavelength i.e. E depends upon v (nu).
- Or E=hv (where v is frequency)
- Value of h =6.634 x 10
^{-34}Jsec

- 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__

__Following observations were made__

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

Please note hv_{o} 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**:

- Calculate the energy of a mole of photons of radiation whose frequency is 5 x 10
^{14}Hz?

Answer 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:-

.