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Electromagnetic radiation can be pictured as a stream of discrete energy packets rather than a continuous wave — a genuinely strange idea that turns out to explain everything from why gamma rays are dangerous to why a dim blue light can do something a bright red one cannot.
What you'll be able to do
Electromagnetic radiation can be modelled as a stream of discrete packets of energy called . Each photon is massless, travels at the speed of light, and carries an amount of energy determined solely by the frequency of the radiation.
Tip — Higher frequency (shorter wavelength) always means MORE energetic photons — this is exactly why gamma rays and X-rays, at the high-frequency end of the spectrum, are so much more dangerous than radio waves of the same intensity.
Photon (and particle) energies in atomic and quantum physics are often extremely small in joules, so a more convenient unit — the — is commonly used. One electronvolt is the energy transferred when a charge of one electron charge moves through a potential difference of one volt.
Tip — Always convert electronvolts to joules BEFORE using E=hf or any other SI-based equation — mixing eV directly into an equation expecting joules gives an answer wrong by a factor of 1.60×10⁻¹⁹.
Equation recap
Common mistakes to avoid
Key takeaways
Test yourself
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