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Quantum Theory of Light |
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Electromagnetic spectrum
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- All objects emits electromagnetic radiation.
- Cold objects \(\rightarrow\) waves with low frequency (Eg: radio waves, microwave)
- Hot objects \(\rightarrow\) waves with higher frequency (Eg: visible light and ultraviolet radiation)
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Black body |
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An idealised body that is able to absorb all electromagnetic radiation that falls on it.
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Thermal radiation |
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Electromagnetic radiation which includes visible radiation and radiation that cannot be seen by the human eye such as infrared radiation.
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Classical Theory
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- The particle nature of light (Isaac Newton)
- Unsuccessful in explaining the phenomenon of light refraction due to failure in comparing the speed of light in glass and air
- Double-slit experiment (Thomas Young)
- Unable to explain the radiation spectrum produced by black bodies
- Dalton atomic model
- Unable to explain the light spectrum produced by atoms
- Discovery of electrons
- Unable to explain the line spectrum of light produced by atoms
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Quantum theory
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- Max Planck
- Introduced the concept of quantum (discrete energy) in 1900
- Albert Einstein
- Einstein's quantum theory of light was susccessful in explaining the characteristics of the photoelectric effect that could not be explained by classical theory
- Niels Bohr
- Explained the production of line spectrum by hydrogen atoms
- Louis De Broglie
- Introduced the hypothesis on the wave nature of particles in 1924
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Electromagnetic spectrum may be a:
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- Continuous spectrum
- Line spectrum
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Continuous spectrum |
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The dispersion of white light by a prism consisting of seven visible colours.
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Line spectrum |
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Produced by an excited atom is a series of colored lines with unique wavelengths and frequencies.
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Photon energy, \(E\) |
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\(E=hf\),
where \(h\) = Planck constant (\(6.63\times10^{-34} \text{ J s}\)
\(f\) = frequency of light waves
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Wavelength, \(\lambda\) |
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\(\lambda = \dfrac{h}{mv}\),
where \(m\) = mass of particle,
\(v\) = velocity of particle
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