# Ejected Electrons with 0 KE?

So I was taught that:

Kinetic Energy (of electron) = Energy (of photon) - Ionization Energy

If E(photon) = IE, then KE=0 of the electron.

What does this physically/theoretically mean?

My current thoughts/interpretation is that enough energy/force is applied to ionize the electron so it is 'sufficiently far' from the atom, and then I guess it just moves with whatever speed it is moving at with natural kinetic laws, since no more energy/force is being applied....?

Any clarifications would be greatly appreciated, thanks in advance.

• It simply means that it's speed after ionization will be zero, anyway you should be aware of that this is idealization that the electron left the potential well of the atom, thus in quantum physics this little bit different.. – TMS Dec 2 '12 at 21:11
• hmm, so is it like the speed of the electron decreases as it is pulled away from the atom..? Because it wouldn't make much sense for it to just stop after being ionized, right? – student Dec 2 '12 at 22:04
• Why not? imagine you are rolling a ball "across" a road of sand, if you give it a very big speed at start it will decrease due to friction with sand until it reaches the other side, and then will continue to move at constant speed (supposing that out of the road is very smooth), now if you give it less energy but at the same time enough to reach the other side of road, it's speed will continuously decrease but it will stop once reaches the edge. – TMS Dec 2 '12 at 22:12
• Well, atoms are always continuously moving with some speed, because they are never at 0K temperature. They are always moving/vibrating with some KE /viceversa. But so in the case of an electron, if it just 'stopped', is it at absolute zero temperature..? Doesn't it have SOME KE/movement? – student Dec 2 '12 at 22:17
• Yes you absolutely right, this why I said from the beginning that this an idealization, because this thermal vibration of atoms/electrons is usually negligibly small comparing to ionization energy. – TMS Dec 2 '12 at 22:21