Glossary / History of physics
Bohr model
The 1913 model in which electrons circle only on certain orbits and emit light of definite energy when jumping between them.
In 1913 Niels Bohr assumed that an electron on certain orbits (stationary states) emits no light, and emits a single quantum of light, carrying the energy difference, only when it moves to another orbit[1]. From this the wavelengths of hydrogen's light could be calculated from basic quantities such as the electron's mass and charge.
For ionised helium it agreed with experiment to five figures, yet why electrons could take only certain orbits, and why they did not radiate on them, went unexplained. Those questions led on to quantum mechanics.
Related terms
- Planck constantThe fundamental constant, written h, that sets the step size of energy for light and matter. Frequency times h is the smallest unit of energy for that light.
- Fine structureThe splitting of what looks like a single line in an atom's spectrum into several closely spaced lines when examined in detail.
- Correspondence principleThe principle that quantum results must agree with classical physics in the limit of large quantum numbers — large objects and high energies.