Physics
Photon Interactions with Matter
Quick fact
When a photon is absorbed by an atom, the atom's electron jumps to a higher energy level; when it drops back, a new photon is emitted—this is exactly how neon signs glow.
Why this is interesting
You see a red apple—but why is it red and not blue? The answer lies in how photons, the particles of light, bounce off or get swallowed by the apple's skin.