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Energy spreads in waves of electromagnetic radiation, like the
ripples on a pond. It travels through space at the speed of light,
around 300,000 km/sec (186,000 miles/sec). Although energy
always travels through space at the same speed, its wavelength (the
distance between any two peaks or troughs of the waves) can vary.
Short waves, such as X-rays, carry high amounts of energy that can
penetrate the human body, while longer, lower energy waves, such
as light, cannot. Apart from visible light, all electromagnetic waves
are invisible. Together these waves make up a continuous band of
energy known as the electromagnetic spectrum.Electromagnetic
GAMMA RAYS
Gamma rays are produced
by radioactivity, such as
a nuclear explosion. They
have a short wavelength
and carry large amounts
of energy. They are very
harmful to humans, but
are used to treat cancer
by killing damaged cells.WAVELENGTHS
The difference between
wavelengths at either end
of the electromagnetic
spectrum is immense.
The wavelength of
gamma rays is only
a fraction of the size
of an atom, while
radio waves at the
opposite end of
the spectrum can
be thousands of
kilometres long.X-RAYS
These high-energy waves
can pass through materials
such as flesh and suitcase
plastic, but not through
bone or metal objects. This
makes them a valuable
tool for examining bones
in hospitals and searching
for weapons in airports.ULTRAVIOLET RAYS
With a slightly shorter
wavelength than visible
violet light, ultraviolet rays
also carry more energy than
visible light. Ultraviolet rays
emitted by the Sun and
tanning beds can damage
skin not protected by
sunblock, causing sunburn.VISIBLE LIGHT
The Sun emits most of its
energy as visible light, which
can be split into the colours
of the rainbow. Earth’s
atmosphere allows visible light
through, while blocking more
harmful wavelengths. Visible
light is vital for life. Without
it, plants could not grow.112_113_electromagnetic.indd 112 10/01/19 2:26 PM