Transcript What is a Spectrum?

What is a Spectrum?
How much of observed light is
high energy radiation
and how much is
low energy radiation.
Nature of Light
Properties
Short wavelength, λ
Long wavelength, λ
High Frequency, ν
High Photon Energy
Blue
Low Frequency, ν
Low Photon Energy
Red
Small Amplitude - Faint
Low Photon Flux
Faint
Large Amplitude - Bright
High Photon Flux
Bright
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What is a Spectrum
• Brightness or Intensity as a function of Energy
– Flux as function of Energy
– How many photons have what energy?
– How many waves of a certain wavelength or frequency have what
amplitude?
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How many photons (brightness or flux) have what
energy (wavelength, frequency)?
Low energy
High energy
High energy
Low energy
…more
high energy
(blue)
photons.
In the wavelength range
450nm to 750nm,
the Sun emits…
Particle (photon) view of light
…fewer
low energy
(red)
photons.
What is the amplitude (brightness or flux) of light
waves of different energy (wavelength, frequency)?
Low energy
High energy
High energy
Low energy
…short-wave
(blue) light with
large amplitude.
Wave view of light
In the wavelength range
450nm to 750nm,
the Sun emits…
…long-wave
(red) light with
small (or low)
amplitude.
What is a Spectrum
• Brightness or Intensity as a function of Energy
• May equivalently shown be shown as a function of
wavelength or frequency
• Describes the energy distribution of the observed light, or
• Describes how much of the observed light has what energy
value
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