MadSci Network: Physics

Re: Can UV photons (energized mercury atoms) induce an electric field?

Date: Mon Mar 7 14:31:47 2005
Posted By: Lawrence Skarin, Rochester Museum and Science Center Technical Assistance Group
Area of science: Physics
ID: 1109597148.Ph

Hello Gonzalo,

Let's slow down a bit and define terms.  Let's agree on a description of a 
mercury atom.

It's got 80 protons in its nucleus, and has 80 electrons spinning round 
it, each in the lowest energy orbit allowed. It has no unbalanced charge, 
and the outside world can consider it an uncharged particle and it 
is 'unexcited'.

If an outer orbit electron is given some energy (say by absorbing a 
photon) and it jumps to a higher level (there's more than one), the atom 
is said to be 'excited'.  This is not a stable state, and soon the 
electron will fall back to its lowest level , sometimes directly , 
sometimes stopping at intermediate levels.  Each time it jumps down, a 
photon with energy equal to the level jump will be emitted.

Photons are not charged particles.  They are the quanta (plural of 
quantum) of light energy.  Photons are electromagnetic waves : they have 
no mass and no charge.  No charge means neither an electric nor magnetic 
field will affect their travel, which is always at light speed in vacuum 
or whatever medium they are traveling through.

Note that an excited atom is NOT a photon.  But it makes photons as it 

Here's a nice java applet animating the phenomenon in a hydrogen atom from 
our friends at the University of Guelph in Ontario.

To the extent that emitted photons do represent a high frequency 
electromagnetic field, I guess you can say the process of exciting and 
deexciting do represent reverses.  But it's an unusual way to express the 

It's always a good idea to use standard descriptions whenever possible.

Larry Skarin

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