Communication
Topic 2: The Electromagnetic Spectrum
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT Point(s)
 identify the limited range of wavelengths of the electromagnetic
spectrum detected by humans and compare this range with
those of other vertebrates and invertebrates
 use available evidence to suggest reasons for the differences in
range of electromagnetic radiation detected by humans and
other animals (this is on the handout you’ll get for homework)
Introduction
The Electromagnetic spectrum is a major stimulus that impacts on
our senses.
It is a range of energy forms that all travel at the speed of light
(300 000 000m/s) but have different wavelengths and frequencies.
These energy forms are disturbances of electrical and magnetic
fields rather than disturbances of a material medium such as water.
This is why they are called electromagnetic radiation.
www.takechargemama.com
The Electromagnetic Spectrum
 Electromagnetic radiation
travels in waves.
The distance between successive
crests of a wave is called a
wavelength (λ). The symbol for
the speed of light is (c). This
comes from the Latin word
‘celeritas’ meaning swiftness. The
frequency (f) is the number of
waves that pass a point in a second
and is measured in hertz (Hz). 1
Hz is one wave (or wavelength)
passing a point each second.
www.acecrc.sipex.aq
The Electromagnetic Spectrum
The mathematical equation that connects these three quantities is:
c = λf
www.chemistryland.com
The Electromagnetic Spectrum
Electromagnetic waves all travel at the speed of light but differ in
their wavelengths. So they range from very short gamma rays and
X-rays with wavelengths of 0.001μm or less to very long radio
waves with wavelengths of 1 or more meters.
timitzers.deviantart.com
The Electromagnetic Spectrum
Since all electromagnetic radiation travels at the speed of light, the
longer wavelengths have shorter frequencies and the shorter
wavelengths have higher frequencies. A spectrum is a range of
wavelengths hence the term electromagnetic spectrum.
imagine.gsfc.nasa.gov
The Electromagnetic Spectrum
 Visible light is somewhere in the middle of the electromagnetic
spectrum with wavelengths of 400-700nm.
All other forms of electromagnetic radiation will pass us by
undetected. The only range of wavelengths the human eye can
detect are those of visible light.
9-4fordham.wikispaces.com
Visible Light
Newton (1643-1727)
discovered that if a beam of
visible light is passed through a
prism, it can be broken up into
the seven colours of the
spectrum. This splitting of
white light is known as
dispersion. These are the
colours of the rainbow with
which we are all familiar: Red,
Orange,Yellow, Green, Blue,
Indego, Violet
www.symbolicliving.com
Visible Light
 Most humans are able to see all of the wavelengths (colours).
Studies have shown that the greatest sensitivity to light in humans
is in the green range of the spectrum.
lisathatcher.wordpress.com
Visible Light
Objects tend to absorb some wavelengths of light and reflect
others. Objects appear coloured because of the light that they
reflect. White light is a mixture of all the colours of the spectrum
so when white light falls on an object like a green leaf, green light
is reflected off the object into our eyes and this is the colour we
see. The other wavelengths are absorbed and not detected by our
eyes.
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Visible Light
When an object appears black, it is absorbing all of the light that
falls on it. A white object reflects all of the wavelengths of light
that reach it. The human eye has evolved to see colours in bright
daylight.
www.gtspirit.com
Visible Light
 We have receptors that are
sensitive to light mainly in
three regions of the spectrum:
red, green and blue
wavelengths.
 This is termed trichromatic
vision.
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Invertebrates and Other Vertebrates
Most living organisms have a
visual range close to that of
humans, however some are very
different.
 Many insects, including
honeybees, are able to detect
wavelengths in the ultraviolet
range of the spectrum.
Their light sensitive cells can
detect the shorter wavelengths
present in the electromagnetic
spectrum.
commons.wikimedia.org
Invertebrates and Other Vertebrates
UV patterns on flowers that attract bees may have a ‘bullseye’
pattern, directing bees to the pollen and nectar in the centre of the
flower.
www.dailymail.co.uk
Invertebrates and Other Vertebrates
Honeybees are unable to detect some of the longer wavelengths in
the red part of the spectrum. It is thought that they see red objects
as black of the absence of colour. Therefore honeybees do not see a
wider range of colours than humans, but rather a different range
(from Ultraviolet through the blue and green range but not red).
photographyoftheinvisibleworld.blogspot.com
Invertebrates and Other Vertebrates
Most studies of colour vision in
insects use honeybees as a
model animal, but recent
research involving the use of
butterflies indicates that they
may have even more visual
pigments and receptor sites
than honeybees. This suggests
that some butterflies may be
able to detect a greater range of
colours than honeybees or
humans.
www.angkorcbd.com
Invertebrates and Other Vertebrates
 Many bird species are able to
detect light well into the
ultraviolet range of the
spectrum.
In addition to this birds tend to
be able to detect light most
efficiently in the red (longer
wavelength) and green ranges of
the spectrum.
outandaboutincooloola.blogspot.com
Invertebrates and Other Vertebrates
They are also able to detect light in the blue range, suggesting
tetrachromatic vision. Some studies on pigeons have even led to
suggestions of pentachromatic vision in birds.
www.ghuth.com
Invertebrates and Other Vertebrates
Sensitivity to light in the near
UV range, previously thought to
occur only in insects and birds,
has been found to be present in
some reptiles like geckos and
rodents such as mice. The blue
cone receptor in mice are
actually UV sensitive.
physicsworld.com
Invertebrates and Other Vertebrates
Many animals that are able to fly are also able to detect polarised
light which humans cannot. Polarisation of light is through to be
used by these animals for navigation during flight.
photographylife.com
Homework
-Students to complete DOT Point 2.4 Range of
electromagnetic radiation detected by humans and other
animals