# Emission and absorption? confused!

1. Oct 6, 2011

### J-Girl

emission and absorption?? confused!

hiii, im just wondering if anybody can give me a very simple definition of each of the two terms, and what the main difference is. Is emission when a wave enters a denser medium (from air to water)? and absorption when a wave enters a medium of lower refractive index number?- just a guess lol, but anyways, would really appreciate some input!:)

2. Oct 6, 2011

### Staff: Mentor

Re: emission and absorption?? confused!

Are you talking about emission and absorption spectra?

3. Oct 6, 2011

### J-Girl

Re: emission and absorption?? confused!

sorry i should have specified, yes emission and absorption spectra. not stated clearly in my book and im spose to learn this! i just cant find a good definition on the internet

4. Oct 6, 2011

### Staff: Mentor

Re: emission and absorption?? confused!

A google search will turn up more explanations, and better ones, than you'll get on PF.

But I'll give a brief explanation to get you going. If you heat the vapours of some substances, the vapour emits light of characteristic colour/s, the exact colour being determined by the arrangement of the electrons in the atoms of the particular elements in that substance. This emitted light is the emission spectrum, and you can see it in things such as neon lights, or coloured fireworks, or school science lab experiments, and even your kitchen gas stove.

An alternative arrangement is to shine white light through the gaseous state of a substance, and use precison optical instruments to examine the light that passes through. You will find some of the individual colours that were in the white light have gone missing, or are at least reduced, because they have been absorbed by the atoms in the vapour. This is the absorption spectra. You need something better than an untrained naked eye to see this effect. Again, the colours that go missing are characteristic of the elements in that vapour.

To excite a substance to the point that it glows and emits light, it is sprayed into a gas flame.

Last edited: Oct 6, 2011
5. Oct 6, 2011

### DaveC426913

Re: emission and absorption?? confused!

Yeah, if you're talking about spectra.
Emission sprectra is when something hot glows in it own characteristic spectrum.
Absorption is when something cold absorbs (ideally white) light in its own characteristic spectrum.

6. Oct 6, 2011

### Staff: Mentor

Re: emission and absorption?? confused!

Yes, that's a good point. A gas, but not heated, not necessarily, anyway. I'll amend what I wrote.