Question about absorption line spectra

[songoku]

Homework Statement

A beam of light consists of a continuous range of wavelengths. The light passes through a cloud of cool gas. The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction grating. Explain why this spectrum contains a number of dark lines

Relevant Equations

Absorption line spectra

The answer from answer key is electrons in gas absorb photon energy and causes electron to move to higher energy level. When electrons de-excite, photons emitted in all directions so dark lines occur.

My question is if photons are emitted in all directions when electrons move from higher to lower energy level, is there possibility that some photons are actually emitted in the direction of the screen so the wavelengths that should be missing turn out to be seen on the screen?

Thanks

 

[kuruman]

My question is if photons are emitted in all directions when electrons move from higher to lower energy level, is there possibility that some photons are actually emitted in the direction of the screen so the wavelengths that should be missing turn out to be seen on the screen?

Yes, and you can estimate the fraction of photons of a particular wavlength that reach an area element $dA$ on the screen for any particular absorption line. It's a simple calculation for which you need to know the distance from the source to the screen.