THE ELECTROMAGNETIC
SPECTRUM
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LIGHT IT UP
•Electromagnetic energy is commonly
known as light.
•There are many types of light energy –
visible light, infrared, ultraviolet and Xrays are all forms of light energy.
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PROPERTIES OF LIGHT
Crest – the highest point on a wave.
Trough – the lowest point on a wave.
Rest Position – the level of a fluid (like
water) when there are no waves passing
through it.
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WAVES OF LIGHT
•We can use the wave properties of light
to differentiate between different types of
energy.
•Frequency is the number of cycles of a
wave that pass a given point in a second.
This basically means how many time each
second a crest (or trough) pass by a given
point.
•The frequency of a light wave totally
depends on its wavelength since all light
travels at the same speed – which is
300,000,000m/s!!!.
•Let’s think about this using mopeds and
busses!
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FREQUENCY 2.0
•The waves below can illustrate what frequency
means in terms of cycles per second. (A cycle is
crest-to-crest or trough-to-trough.)
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WAVELENGTH & COLOUR
•The electromagnetic spectrum has light
rays that differ based on their frequencies
– this means they must have different
wavelengths!
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THE SPECTRUM 1.0
•We can separate visible light into a
continuous spectrum – an uninterrupted
pattern of colours. (Light through a prism.)
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The SPECTRUM 2.0
•We can also see what is known as a line
spectrum when energy is emitted
(released) from various types of matter.
•The line spectrum is discontinuous and
can be used to identify a specific element.
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ELEMENT FINGERPRINTING
•Each element gives off its own line
spectrum with its own pattern of colours
based on the energy the electrons absorb
and release. (We just saw this…)
• A device called a spectroscope allows us
to see the bands created by separating
light
energy
into
its
component
wavelengths/colours.
•The spectroscope basically catches the light energy
released from the electrons as they release the energy they
absorb…our eyes blend the rays into one colour but the
spectroscope keeps them separated – producing the
characteristic bands used to indentify the element.
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EMISSION SPECTRUM
•This video explains why each element
gives off its own unique pattern of light.
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•http://www.youtube.com/watch?v=QI50GBUJ48s Page 10
SO WHAT HAPPENED?
•The atom absorbed the energy of the
flame and the valence electrons absorbed
that energy and got excited and jumped
up to a higher orbit or energy level – we
can’t see this. The electrons are now said
to be in an excited state.
•BUT – they must return to their most
stable position which is closest to the
nucleus – the ground state.
•In order to do this they must give off the
energy they absorbed and when they do
this it is given off as light energy.
•The distance between the excited state
orbit and the ground state orbit will
dictate
the colour of the light emitted.
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FLAME TEST RESULTS
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THAT’S ALL FOLKS!
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