To determine the Rydberg constant by studying Hydrogen spectrum.
Balmer series is the emission spectrum associated with the transition of electrons from states with the principal quantum number n>2 to the state with n = 2. The wavelengths of the corresponding lines are expressed by a formula
where, n1 = 2 and n2 > 2.
In Hydrogen spectrum, there are a few bright lines, namely
Hα : n2 = 3 : Colour = Red
Hβ : n2 = 4 : Colour = Blue-green
Hγ : n2 = 5 : Colour = Violet
Hδ : n2 = 6 : Colour = Violet
In the present experiment wavelengths of these lines are determined by measuring the angle of diffraction by a transmission grating using the formula
Here α is the width of the opaque line in the grating and b is the width of the transparent region between two opaque lines and consequentlywhere N is the number of rulings per unit length of the grating, n is the order of the spectrum and θ is the angle of diffraction.
Spectrometer, Spirit level, Hydrogen discharge tube, Power supply for the discharge tube. (A magnifying lens and a torch in hand may prove useful)
- Vernier Constant of the Spectrometer:
- Measurement of angle of Diffraction:
No. of Rulings N = ………………. per mm.=……………… per cm.
RH from red line=
RH from blue-green line =
RH from violet-1 line=
RH from violet-2 line =
Average RH =
Standard value of RH =