travelling in circles at the speed of light

Anyone here into physics?

I read that electrons travel at the speed of light in a vacuum.
What about when an electron is part of an atom?
Is it travelling round in circles at the speed of light?

Quantum physics tells us that the electron's location is uncertain until we measure it so is it simply nonsense to try and talk about an electron's velocity when it is part of an atom?
Is it the case that we have to use the particle model of an electron when it is "free" and the wave model when it is trapped around an atomic nucleus? Does an atomic electron have velocity?

I like the mental image of travelling in circles at the speed of light. Sounds like a 70s prog album title.
 
>mms

yeah, you know, I am back to thinking about that stuff.
I was hoping someone on here could shed some light, maybe I should email your lady professor friend again....
 

turtles

in the sea
Edward said:
Anyone here into physics?
Sure! Aren't there any other science nerds in this place??

I read that electrons travel at the speed of light in a vacuum.
What about when an electron is part of an atom?
Is it travelling round in circles at the speed of light?
I'm not 100% certain on this (it's been awhile since i took any physics classes), but I'm pretty sure the answer is no. Basically since electrons have mass (though it is very small), it would require a large amount of energy to crank it up to the speed of light, and since electrons can exist at different energy levels (quantums) within an atomic orbit, i would assume that means they'd be moving at a speed less than the speed of light. Looks like wikipedia backs me up too--electrons can only approach the speed of light in a vacuum.

(and it's not really correct to say electrons travel in circles anyway, they travel in much more fun looking orbitals)
orbitals.jpg


Quantum physics tells us that the electron's location is uncertain until we measure it so is it simply nonsense to try and talk about an electron's velocity when it is part of an atom?
Is it the case that we have to use the particle model of an electron when it is "free" and the wave model when it is trapped around an atomic nucleus? Does an atomic electron have velocity?
You're missing the other half of the Heisenberg Uncertainty Principle, in that if you know an electron's position, you can't know it's velocity, but if you know an electron's velocity, you can't know it's position. So it is reasonable to talk about an electron's velocity. Generally I think it's all spoken of in probabalistic terms anyway, with probability curves for position and velocity giving you a rough idea where and at what speed electrons are travelling.

I like the mental image of travelling in circles at the speed of light. Sounds like a 70s prog album title.
Sorry for messing with your mental image ;) but i agree, it does sound good. Going around in circles as fast as possible seems like a very modern thing to do...
 
So all we can really say about electrons in atoms is what energy level they are at.

I guess the atom is small enough to be close to the limits of how accurately you can guess either the speed or the velocity of something anyway.
Or not so?

The Planck length is a lot smaller than the diameter of an atom.
hmm...


Thanks for your reply.

I think I will still use the album title!
 

Mr. Tea

Let's Talk About Ceps
Hmm. Couple of points worth making here:

Firstly, electrons - having mass - can NEVER travel at the speed of light. It would take not merely a 'large' amount of energy to make them travel at light speed, but an *infinite* amount of energy. In other words, it can't happen. Only massless particles (like photons - particles of light itself) can travel at light speed. (In fact, they can ONLY travel at this speed).

Secondly, particles moving in a circle are accelerating, and accelerating electic charges - like elctrons - give off radiation. The tighter the circle or the higher their energy, the more radiation they give off. This is why the next big electron/positron collider will be a linear accelerator, because electrons in circular accelerators simply lose too much energy.

http://en.wikipedia.org/wiki/Lep this one is closed down now
http://en.wikipedia.org/wiki/International_Linear_Collider this one is under conceptual development

Edit: just read the stuff about electrons in atoms. Yes, you can still talk about an electrons expected, or average, speed when it's part of an atom - although measuring its actual speed (technically, velocity) at any one time would mean you can't have any knowledge about it's position. This is one incarnation of the famous Heisenberg U. P.
Electrons in some atoms move very fast indeed - in fact, I remember hearing (a long time ago) that gold has the colour it does because it's such a big atom the outer electrons have to travel close to the speed of light, and a relativistic correction causes the light reflected by such atoms to have a yellowy (rather than whitish) colour.

It's worth mentioning that electrons in atoms aren't *really* moving in circles, like planets around the Sun - if they did, they'd give off radiation (as described above), lose energy and rapidly spiral into the nucleus. Instead they exist as 'probability waves', as someone mentions above with the diagrams of various atomic excitations.
 
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