In this theory, atomic model of Bohr is explained here.

Bohr’s Atomic Model

The atomic model is proposed by Bohr in 1913. The Bohr has made following assumptions.

The atom has massive positive charged nucleus.
The electrons revolve round their nucleus in circular orbits.
The centrifugal force between electron and nucleus is balanced by electrostatic pull.
The electron cannot revolve round the nucleus in any arbitrary orbit but certain definite discrete orbits (stationary orbits).
The orbital angular momentum of the electron is equal to an integral multiple of h/2π
Orbital angular momentum = nh / 2π
Where n = Integer, h = Planck’s constant
The electrons do not radiate out any electromagnetic energy while revolving in the stationary orbits. In other words. the orbits are non-radiating path of the electron.

Frequency of Emitted Photons

When electrons jump from one orbit to another orbit, the atom radiates out energy.
If E1 and E2 are the energy of the two orbits before and after electron jump, the frequency of the emitted photon is given by

E1 – E2 = hf

ΔE = hf

Where f = Frequency of the emitted radiations

ωI = nh / 2π

( mr² ) ω = nh / 2π

( mr² ) ( v / r ) = nh / 2π

mvr = nh / 2π

The n is called as principal quantum number or Bohr’s circular orbit and it is first, second and third orbits etc…. If fixes the size of allowed orbits

= 1, 2, 3 etc