Energy levels and photon emission Flashcards – AQA A-level Physics (7408)

An electron falls from energy level $E_1$ to a lower level $E_2$. What is emitted, and what is its energy?

A photon is emitted with energy $hf = E_1 - E_2$, where $h$ is the Planck constant and $f$ is the photon frequency.

Why does an atomic emission spectrum contain discrete lines?

Atomic energy levels are discrete, so only particular energy differences and photon frequencies are possible.

What does the line emission spectrum of atomic hydrogen provide evidence for?

Quantised atomic energy levels.

What is an electronvolt, and how many joules is one electronvolt?

It is a unit of energy: $1\,\text{eV} = 1.60 \times 10^{-19}\,\text{J}$.

When calculating photon frequency using the Planck constant in joule seconds, what unit must be used for the energy difference?

Joules.