i. According to Bohr’s third postulate, when an electron in a hydrogen atom jumps from higher energy level to the lower energy level, the difference of energies of the two energy levels is emitted as a radiation of particular wavelength called spectral line.
ii. The wavelength of the spectral line depends upon the energy associated with the two energy levels, between which the transition of the electron takes place.
iii. If the energy absorbed is equal to difference between the energies of the two levels then it jumps to a higher permitted orbit and revolves in it. In this case, electron is said to be in the excited state.
iv. In the excited state, the electron is not stable and tries to attain stability by going back to the ground state by emitting the extra amount of energy it had gained in one or more jumps.
v. The energy is emitted as electromagnetic waves and produces a spectral line of the corresponding frequency or wavelength.
Bohr’s formula for spectral lines in hydrogen spectrum:
i. Let, En = Energy of electron in nth higher orbit
Ep = Energy of electron in pth lower orbit
ii. According to Bohr’s third postulate,
iv. From equations (1), (2) and (3),
where, c = speed of electromagnetic radiation
Equation (4) represents Bohr’s formula for hydrogen spectrum.
Given: μg = \(\frac{3}{2},\) μw = \(\frac{4}{3},\) vw - vg = 0.24 × 108 m/s
To find: Velocity of light (c)
Formula: μ = \(\frac{c}{\text{v}}\)
Calculation: From formula,
Velocity of light in air is 3 × 108 m/s.
