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 energies 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 as a supernova |
|
X – Radiation |
High energy changes in electron structure of atoms Produced when electrons collide with other particles or are decelerated |
X ray tubes |
|
Ultraviolet |
Fairly high energy changes in electron structure of atoms |
Very hot bodies Produced when electric current is passed through gases at very high 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 emits infrared radiation |
|
Microwaves |
Produced by changes in the vibrations of atoms in molecules |
All matter The Universe contains a lot of microwave radiation left from the Big Bang – when the Universe was born |
|
Radio |
High frequency electric circuits Very low energy changes in molecules |
Radio transmitting circuits and aerials |