Heat an element in a flame, and it gives out its own colours. Hydrogen gives a few sharp lines, and not a smooth rainbow. In this course we learn how light behaves as a wave and as a stream of particles, how the lines of hydrogen are counted, and how Bohr explained them with energy levels, with numbers that you can check.
4 lessons, about 1 h 40 min4 simulations12 problems8 practice questionsPython in every lesson
Light is an electromagnetic wave. Its speed in vacuum is c = 3.00 × 10⁸ m/s, and c = νλ links the frequency and the wavelength. The wavenumber is 1/λ. Visible light is a narrow band, from about 400 nm to 750 nm.
Planck said that energy is given out in packets, . Einstein used this to explain the photoelectric effect: light is a stream of photons, each of energy , and . Light behaves as a wave and as a particle.
An element gives out light of certain wavelengths only, a line spectrum, which is its fingerprint. The lines of hydrogen fall in series, and all of them follow the Rydberg formula, wavenumber , with .
Bohr said that an electron in a hydrogen-like atom can be only in certain circular orbits, with energy and radius . It gives out or takes in a photon of energy hν when it jumps between orbits. This explains the lines of hydrogen.
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