Question

Astronomers use diffraction gratings to study the spectra of light from stars. For stars like the Sun, Calcium produces a pair of spectral features called the H and K lines at wavelengths of 396.9 nm and 393.4 nm, respectively. One of the spectrographs on the Keck telescope contains a diffraction grating with 1200 lines/mm. What is the angular separation between the H and K lines in the second order produced by this spectrograph?

Astronomers use diffraction gratings to study the spectra of light from stars. For stars like the Sun, Calcium produces a pair of spectral features called the H and K lines at wavelengths of 396.9 nm and 393.4 nm, respectively. One of the spectrographs on the Keck telescope contains a diffraction grating with 1200 lines/mm. What is the angular separation between the H and K lines in the second order produced by this spectrograph?

71.4 degrees

73.0 degrees

3.2 degrees

0.3 degrees

1.6 degrees

Answer 1

Given there are 1200 lines in 1mm of the grating. The separation between adjacent lines of the grating are

The condition of maximum for diffraction grating is

The angular separation between two lights is

Substituting , , n=2