Question

(a) Use Rydberg formula to calculate the wavelengths of the four visible lines in the
Balmer series of light emitted by a hydrogen gas-discharge lamp. A diffraction grating of
width 1 cm has 2000 slits. It is used to measure the wavelengths of the visible spectrum of
hydrogen. (b) Determine the first-order diffraction angles of the four observed lines. (c)
What is the angular width of each one of them?

Answer 1

In visible spectrum for H the Balmer series is given by -

Now, since there are 2000 slits in 1 cm, then slit spacing, d = 5002.50 nm.

So by using the following relationship;

where m is the order of diffraction and θ is the diffraction angle. for first order, i.e., m=±1, we get -