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Light and Atoms
Chapter 3
Properties of Light
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It does not need a medium (substance
to travel through)
need air or water to
travel through.
There is no sound in space
Manifestations of Light
Light can be explained by
models
1. Light as a _______
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wave – A wave consisting of
alternating electric and magnetic energy.
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– Ex. Visible light, color depends on wavelength.
2. Light as a ____________.
 Light is also considered a subatomic particle
that in empty space travels in a straight line at
the speed of light.
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– A particle of visible light or other
electromagnetic radiation.
When to use a specific
model?
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Scientist use whichever model best explains
the properties of light at any given time.
When they explain how a lens focuses light
they use the wave model.
When they want to explain how light
bounces off of a mirror they use the particle
model.
Light is described as having ____________
_____________.
Light and color
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_______________ – The portion of
electromagnetic radiation that the human
eye is sensitive to.
– Red, orange, yellow, green, blue, indigo, and
violet
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The difference in color is due to the
difference in wavelength.
Wavelength – Wavelengths of light are measured in
nanometers.
Various Laws related to
light
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Wien’s law
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– Remember higher energy light has higher
frequency and shorter wavelengths.
Various laws related to
light
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Stefan’s law –
When Stefan’s law and Wein’s law are
both applied we are able to determine
that as temperature increases so does
the intensity of light
Various laws related to
light
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Kirchhoff determined that there are 3 different
kinds of spectra.
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– light we see via a prism
– light we see emitted from a source.
Shows lines from the wavelengths emitted by a
heated element.
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– spectra of light with black lines
(light that was absorbed by a material or gas)
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Kirchhoff’s law –
The Doppler Shift
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If a source of light is in motion, its
spectral lines shift to new
wavelengths.
The Doppler shift results in the
Directions of the Doppler
Shift
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The shift is an increase in the
wavelength if the source and observer
move apart.
The shift is a decrease in wavelength if
the source and observer approach
each other.
The Doppler shift results in a redshift
or blueshift.
Redshift
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A shift in the wavelength of electromagnetic
radiation to a longer wavelength. For visible
light this implies a shift toward the red end
of the spectrum.
Redshifts occur when the source moves
________ from the observer or when the
observer moves away from the source.
If a star moves away from the Earth then its
light will appear more red.
Blueshift
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A shift in the wavelength of electromagnetic
radiation to a shorter wavelength. For the
visible light, this implies a shift toward the
blue end of the spectrum.
The shift can be caused by the motion of
the source of radiation ____________ the
observer or by the motion of the observer
toward the source.
A star moving ________ the Earth will
exhibit a blueshift.
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Our atmosphere also bends light
waves so that most stars have a
similar appearance regardless of what
spectra of light they may be emitting.
Blackbodies
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A blackbody is an object that absorbs
all light that falls on it.
No electromagnetic radiation passes
through it and none is reflected.
Because no light is reflected or
transmitted, the object appears black
when it is cold.
Blackbodies (Continued)
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When a blackbody is “hot”, it is a source
of thermal radiation.
– Incandescent light bulbs are an example of
black bodies.
– The Sun is also an example of a Blackbody
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When a Blackbody is hot enough to emit
radiation, it is termed blackbody radiation
When hot gases emit radiation it is
termed emission-line radiation
Blackbody Radiation
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At room temperature, black bodies emit
infrared light.
As temperature increases past a few hundred
degrees Celsius, black bodies start to emit at
visible wavelengths of light
Blackbody radiation in the visible spectra
ranges from red, through orange, yellow, and
white before ending up at blue,
Beyond blue light, the emission includes
increasing amounts of ultraviolet light.
Parts of the Atom
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– Positively charged particles
found in the nucleus of an atom.
– The identity of an atom is determined by the
number of protons found in the nucleus.
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– Neutrally charged particles
found in the nucleus of an atom.
– Negatively charged particles
spinning around the nucleus of the atom.