Continous spectra - line spectra - the doppler effect

krd

If the continous spectra of hot objects (tungsten in a light bulb), caused by the line spectra of the atoms becoming blurred via the movement of the atoms and the doppler effect?


Or is something else happening?

Same with absorbtion. Does the Doppler effect allow atoms to absorb wavelengths that are not in its absorption spectra?

Capt'n Midnight

single atoms have well defined energy levels for that electrons can occupy

when photons move from one level to another the energy difference can be emitted as light / uv / infra red / heat etc. so you get a series of distinct lines - so monoatomic or ionised gases

when you have molecules or groups of atoms solids or liquids
the energy levels can 'merge' so you get a more continuous spectrum, in fact you can have the opposite effect where the energy gaps of some atoms adsorb strongly and cause dark lines



red shift and blue shift moves these lines , but they stay distinct and don't get blurred.

krd

Capt'n Midnight wrote: »

single atoms have well defined energy levels for that electrons can occupy

when photons move from one level to another the energy difference can be emitted as light / uv / infra red / heat etc. so you get a series of distinct lines - so monoatomic or ionised gases

Yes, I knew this. I even remember doing spectroscopy experiments - where I'm pretty sure, I was able to determine the I can't remember.

Yeah, you get the lines.

But, say if you pump enough electricity through an ionised gas, eventually the lines will disappear and you will get a continuous spectra. Strictly speaking, the lines don't disappear, but you do get a continuous spectra. Like most of the light from the sun is continuous spectra. When we get light from the sun, it's not limited to the lines of hydrogen.

Now I'm not sure what causes the continuous spectra - do excited or free electrons release photons with any old wavelength?

red shift and blue shift moves these lines , but they stay distinct and don't get blurred.

No. I've found out recently in plasma physics - one trick to measure the temperature of the plasma is to watch this Doppler broadening. The velocity of the atoms in the plasma shift the wavelengths of the lines - and the lines broaden.

Red shift and Blue shift, is a shift of either approaching or receding from a continuous spectra. The continuous spectra from stars only appears white for useful evolutionary reasons.

I've been thinking about this. Hot atoms whizzing around - that velocity has to have a shift effect on the emitted wavelengths - I see they use it in plasma physics. I wasn't sure if it caused the continuous spectra we see from something like the sun.

I've also been thinking about this in terms of how wavelengths are absorbed by atoms. If the atom is in motion, that velocity will shift the incoming photon, and if I'm right, the photon will appear either more or less energetic to the atom.

krd

The Doppler effect is far more interesting that just red and blue shift, when you think about it.

It shifts the dimensions of waves relative to each other, and their velocities.

Though I'm not sure about this - I've been thinking. When a photon hits an atom - because of the photons velocity, it would appear to it that it was hitting a flat plane.

krd

From what I've learned.

The continuous spectra is caused by phonons. That's why it's continuous and increases in intensity with temperature. And it's also the reason the peak frequency increases with temperature - the atoms are moving faster creating phonons with higher frequencies.

IRWolfie-

Capt'n Midnight wrote: »

when photons move from one level to another

Just to correct the mistype, it's electrons not photons.

Capt'n Midnight

IRWolfie- wrote: »

Just to correct the mistype, it's electrons not photons.