Transition of Electron

When an electron makes transition from higher energy level having energy E2(n2) to a lower energy level having energy E1(n1), then a photon of frequency Î½ is emitted

Fig. 7

Wave number/wavelength

Wave number is the number of waves in unit length

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Number of spectral lines

If an electron jumps from higher energy orbit to lower energy orbit, it emits raidations with various spectral lines.

If electron falls from orbit n2 to n1, then the number of spectral lines emitted is given by

If electron falls from nth orbit to ground state (i.e., n2 = n and nÂ­1 = 1) then number of spectral lines emitted

Recoiling of an atom

Due to the transition of electron, photon is emitted and the atom is recoiled.

Recoil momentum of atom = Momentum of photon

Also, recoil energy of atom (where m = mass of recoil atom)