Help on Isaac physics D7.13

alliM2007

I've used E=hc/wavelength and I keep getting 0.012nm but it is wrong, does anyone know why? Screenshot 2025-05-18 17.48.02.png

Reply 1

lordaxil

E = hc/λ is only valid for photons (massless). For particles with non-zero rest mass, the de Broglie relationship gives λ = h/p, where p is the momentum. In this case, the electrons have a significant amount of kinetic energy (compared to their rest energy), so you need to use the relativistic expression for momentum. This is most easily calculated by setting kinetic energy T = E - mc² where E is total energy from E² = (pc)² + (mc²)², and then solve for p in terms of T, m and c.

Reply 2

Nitrotoluene

Alright, so de Broglie figured out that a particle's wavelength "λ" is equal to Planck's constant "h" divided by the particle's momentum (p).
First of all, find the electron's momentum "p" from its kinetic energy. As lordaxil said above, use relativistic energy-momentum stuff: Etotal^2 = (pc)^2 + (mc^2)^2. The mass of the electron "m" can be found in official online tables.
You now have all the information needed to calculate "p", which you can then plug into the equation λ = h/p to calculate "λ".
Krgds,
Sandro

(edited 9 months ago)