Origins of Electromagnetic Radiation

Electromagnetic radiation comes in a wide range of energies. Some electromagnetic radiation has energy vanishingly small, while some are so energetic that a single particle can be perceived. When astronauts first went into orbit around the Earth, they told of light flashes when they were asleep. Some of these were due to individual high energy light waves (photons) hitting the retina and causing electrical impulses to be produced. While radiation of different energues may be due to a wide variety of causes, some common ones are summarised in the table below.

Type of Radiation

Origin

Sources

Gamma Rays

Nuclei of atoms or cosmic processes

Radioactive materials or high energy cosmic processes such assupernovae

X – Radiation

High energy changes in electron structure of atoms

Produced when electrons collide with other particles or aredecelerated

X ray tubes

Ultraviolet

Fairly high energy changes in electron structure of atoms

Very hot bodies

Produced when electric current iis passed through gases at veryhigh voltages

Visible

Energy changes in electron structure of atoms

Hot bodies – especially stars

Produced by high voltage gas discharge tubes or lightning

Infrared

Low energy changes in electron structure of atoms

All matter above the absolute zero of temperature emitsinfrared radiation

Microwaves

Produced by changes in the vibrations of atoms in molecules

All matter

The Universe contains a lot of microwave radiation left fromthe Big Bang – when the Universe was born

Radio

High frequency electric circuits

Very low energy changes in molecules

Radio transmitting circuits and aerials

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