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The Challenge: Make an underwater flashlight



Why does the filament glow?

Electricity flowing through the filament is essentially just electrons moving along the wire. The movement of these electrons isn't smooth: as well as moving in one direction, they are also bouncing around, hitting each other. The nuclei of the atoms of the wire form a lattice that the electrons have to move across. The material is described as having a 'resistance' to the electron flow. The more resistance the metal offers, the more electrons bash each other and the nuclei and the hotter the material gets.

The heat energy gets other electrons, still trapped around the metal atoms' nuclei, excited. The energy pushes the electrons further away from the nuclei of the atoms. As the electrons fall back, they emit photons of light.

Close up of filament
Electrons moving along the filament.
 

Electrons moving along the filament