Light and electricity united
In 1800 William Herschel placed a thermometer beyond the red end of a prism's spectrum and discovered invisible infrared light; the next year Johann Ritter found ultraviolet beyond the violet. In 1831 Michael Faraday discovered electromagnetic induction — a moving magnet makes current — and imagined "lines of force". In 1865 James Clerk Maxwell put this into equations and calculated that changing electric and magnetic fields regenerate each other as a wave travelling at the speed of light, concluding that light is an electromagnetic wave. This idea later became a starting point for Einstein's relativity.
Hertz's proof and the spectrum
In 1887–88 Heinrich Hertz made invisible radio waves with a spark apparatus and showed they reflect, refract and interfere, confirming Maxwell; the unit of frequency, the hertz, honours him. Jagadish Chandra Bose in India studied millimetre waves in the 1890s, and Guglielmo Marconi made wireless telegraphy practical. In 1895 Wilhelm Röntgen discovered X-rays, and in 1900 Paul Villard found gamma rays from radium. From long radio waves through microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays, all are the same phenomenon differing only in wavelength. In 1900 Max Planck assumed light energy is exchanged in lumps, and Einstein explained the photoelectric effect by treating light as particles, photons. In 1965 Arno Penzias and Robert Wilson found the cosmic microwave background, supporting the Big Bang.
Electromagnetic waves in daily life and health
Radio and TV, mobile phones and Wi-Fi, microwave ovens, infrared remotes, lasers and medical X-rays and radiotherapy all use electromagnetic waves. Health effects depend strongly on energy. Wavelengths shorter than ultraviolet (X-rays, gamma rays) are ionising — they knock electrons from atoms and can damage DNA, so exposure must be managed — and ultraviolet causes sunburn and skin cancer, so sun protection matters. Radio waves from phones and Wi-Fi are low-energy non-ionising radiation whose main established effect is slight heating. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) sets exposure limits on this basis, and there is no consistent evidence of harm below them, though research on long-term effects continues.
FAQ
- Does a microwave oven make food radioactive?
- No. Microwaves shake water molecules to produce heat; they do not make food radioactive, and they vanish the moment the oven switches off.
- Do mobile-phone emissions cause cancer?
- The WHO's International Agency for Research on Cancer classes radio-frequency fields as "possibly carcinogenic" (Group 2B), meaning evidence is limited. So far there is no consistent evidence of increased cancer risk from use within exposure limits.
Sources reviewed: 2026-10-26
References
- Herschel, W. (1800). Experiments on the refrangibility of the invisible rays of the sun. Philosophical Transactions of the Royal Society of London, 90, 284–292.
- Faraday, M. (1832). Experimental researches in electricity. Philosophical Transactions of the Royal Society of London, 122, 125–162.
- Maxwell, J. C. (1865). A dynamical theory of the electromagnetic field. Philosophical Transactions of the Royal Society of London, 155, 459–512.
- Hertz, H. (1888). Über Strahlen elektrischer Kraft. Annalen der Physik, 272(4), 769–783.
- Bose, J. C. (1897). On the determination of the wavelength of electric radiation by a diffraction grating. Proceedings of the Royal Society of London, 60, 167–178.
- Villard, P. (1900). Sur la réflexion et la réfraction des rayons cathodiques et des rayons déviables du radium. Comptes rendus de l'Académie des Sciences, 130, 1010–1012.
- Planck, M. (1901). Ueber das Gesetz der Energieverteilung im Normalspectrum. Annalen der Physik, 309(3), 553–563.
- Penzias, A. A., & Wilson, R. W. (1965). A measurement of excess antenna temperature at 4080 Mc/s. Astrophysical Journal, 142, 419–421.
- International Commission on Non-Ionizing Radiation Protection (ICNIRP). (2020). Guidelines for limiting exposure to electromagnetic fields (100 kHz to 300 GHz). Health Physics, 118(5), 483–524.