# Hydrogen Gas Transparency With Visible Light

1. Mar 23, 2014

### Neek 007

I'm reading my physics text, Matters and Interactions, and there is an example about why Hydrogen gas is transparent in visible light.

It says it is transparent because visible light has energies from 1.8 to 3.1eV, and in order to move a Hydrogen atom from ground state to the first excited state, requires 10.2eV.

I read online that if a current is passed through a container of hydrogen, some light is emitted, and if this light emitted is put through a prism, 4 bands of light are observed.

So say, instead, only UV light was passed through a container of hydrogen gas, would any atoms rise energy levels? UV light has energy of 100 eV, so this is enough energy, but I could not find anything on the internet about this. What color would this light emitted be, if any light was emitted?

2. Mar 23, 2014

### Staff: Mentor

It depends on the frequency of the UV light used. Look at http://en.wikipedia.org/wiki/Hydrogen_spectral_series for all the details.

For the hydrogen atom to be able to emit in the visible part of the spectrum, it needs to be excited to at least $n=3$, meaning at least 103 nm light (12.0 eV). That would give only one band in the visible. To see all 4 bands, it needs to be excited at least to $n=6$ with 93.8 nm (13.2 eV) light. Anything of higher energy will result in all 4 visible bands being emitted.