# Kinetic Energy of neutron and electron

1. Feb 20, 2016

### Dexter Neutron

Question in my textbook:-
The wavelength of light from the spectral emmision line of sodium is 589 nm.
Find the kinetic energies of electron and neutron at which they both have same de broglie wavelength.

Logically, since light of same energy is falling on both then their kinetic energies must be same thus single answer, but there are two answers given(4.34 ueV, 0.236neV).How could their kinetic energies be different if they are absorbing the same amount of energy?

Mathematically equating the de Broglie wavelength of both gives the relation that momentum of both must be same and their kinetic energies must be in a ratio of 2000:1 same ratio as that of mass.

Why logical and mathematical aspects are different?What mistake I am doing?

2. Feb 20, 2016

Hi Dex,