**Objective:**

To determine the Rydberg constant by studying Hydrogen spectrum.

**Theory:**

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.

**Apparatus:**

Spectrometer, Spirit level, Hydrogen discharge tube, Power supply for the discharge tube. (A magnifying lens and a torch in hand may prove useful)

**Experimental results:**

**Vernier Constant of the Spectrometer:**

**Measurement of angle of Diffraction:**

*No. of Rulings N = ………………. per mm.=……………… per cm.*

**Calculation:**

λ_{red} =

λ_{blue-green} =

λ_{violet-1 }=

λ_{violet-2} =

R_{H} from red line=

R_{H} from blue-green line =

R_{H} from violet-1 line=

R_{H} from violet-2 line =

Average R_{H} =

Standard value of R_{H} =

**Percentage Error:**

**Conclusion:**