# ENERGIES OF SUBATOMIC PARTICLES

So far, we have seen that an electron may exist in the form of various orbitals. A key concept for understanding semiconductor physics, is understanding the allowed energy values for an electron.

# Hydrogen Atom

Once again, we look at a Hydrogen atom that consists of one electron and one proton.

These subatomic particles are equally, but oppositely, charged.

# Coulomb Force

The attraction force between the electron and proton is governed by the Coulomb law:

$F = {q^2 \over 4 \pi \epsilon_0 r^2}$

Here $\epsilon_0$ is permittivity of free space, q is electron charge, and r is the distance between the particles.

# The Potential Energy

The electronâ€™s potential energy at any point in space is the work done by an external force to move the electron from the reference point to that point at a constant velocity.

If we define the potential to be zero at infinity, the potential energy can be calculated as $E_p = {-q^2 \over4 \pi \epsilon_0 r}$

# Total Energy of Electron

The classical model assumed that the electron revolves around the proton, giving rise to a kinetic energy defined by $E_k = {1 \over 2} m v ^2$

# Absorption of Energy

If a photon is shined on a hydrogen atom, the electron may absorb its energy. With the classical model, any photon can be absorbed.

# Observed Transition

However, the experiments show only photos with particular wavelength (hence energy) are absorbed.

Can you find which photon energies are absorbed?

# Unstable orbitals

Moreover, a hydrogen atom in an excited state would can emit a photon and lose energy.

What photon energies are emitted?

# Orbitals and Energy

Can you excited the electron to the 3rd energy level by shining the right photons?