Question

If a helium atom becomes positively charged, a cation, and is at STP, upon collision with an insulator such as a diamond wafer, is the collision elastic? as would be the case with an uncharged helium atom.
Thanks
Stuart

Answer 1

Hi biodelta. Here's a wild guess.
True, if a helium (inert gas, two electrons complete the 1s shell) atom loses an electron it becomes positively charged. If a said atom collides with an insulator, then during the approach to the insulator, it will presumably induce a negative charge on the insulator. That induced charge may serve to accelerate the hapless helium atom towards the insulator. Since unlike charges attract, I'd guess that the helium ion would be "tempted" to stick to the insulator, which I'd further guess would imply that the collision would be inelastic.
In the same sort of way that if two "macroscopic" bodies collide and then stick together making for an inelastic collision. If the said bodies bounce off each other with "perfect coefficient of restitution" then I think that the collision is "perfectly elastic". so that conservations of momentum (that before = that after) and kinetic energy (that before and that after again) hold.
On the way I'm thinking, the elastic collision refers, in energy terms, to kinetic energy which is conserved. An inelastic collision means that kinetic energy is not conserved, but that the energy goes into different forms such that the total energy (ie KE plus the bits you can't account for with a sexy formula) is conserved.
And all this is BEFORE you get to the relativistic versions !
Have fun with the confusion.
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