I encountered a question in my book:(adsbygoogle = window.adsbygoogle || []).push({});

a)An electron is trapped in a solid between a group of atoms where the potential is +2.8V

The de Broglie wavelength of this electron is 1.2nm. Calculate

i) its speed

ii) its kinetic energy

iii) the sum of its kinetic energy and its potential energy

b)i) Calculate the energy of a photon of wavelength 650nm

ii)State and explain whether or not the electron in part a) can escape from this group of atoms as a result of absorbing this photon

I can do the whole question via formulae "taught" to me and find that the resolved kinetic energy after the photon absorption will result in it escaping.

But I have some problems with the question itself, it says the electron is "trapped". I would have thought since it is trapped it was stationary.

Also I do not understand what is trying to get across when it mentions "potential", is this the potential that the electron needs to cross to escape?

I don't think I fully understand potential differences, would placing 2 opposite charges far from eachother and close together result in the same potential difference and consequently the same KE? I always thought that placing 2 charges away from eachother no matter the distance (Electromagnetic force has infinite range) would attract eachother, closing the distance and also increasing the force.

I thought that momentum and KE are both conserved in a closed system. Say you had 2 particles of equal opposing momentums and you collided them both so they both stopped.

Particle 1 - 0.5kg - 1 m/s

Particle 2 - 1kg - 0.5m/s

But Particle 1 has a KE of 0.25J

and Particle 2 has a KE of (relatively) 0.125J

0.25-0.125=0.125J

If both particles are now stationary, where has the extra KE gone when KE is also meant to be conserved?

A lot of questions here, sorry.

Thanks

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Potential difference of a group of atoms

**Physics Forums | Science Articles, Homework Help, Discussion**