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Early Concepts of Light
The only thing we can really ________ is __________. Because of this, it
has been studied for many years. Some of the ancients, thought that light
was made up of tiny __________________ that entered the eye. Others, like
P________, S______________ and E__________, thought that vision
resulted from s__________________ or f________________ that
______________ the eye. This notion of things leaving the eye was shot
down by the ________ ________ ________________.
Until the time of N__________, most scientists thought that light consisted
of __________________. Newton liked the idea that light is a particle
because it explains ____________________ (bouncing of light) and he
thought light’s particle nature explains why light cannot ________________
(go around obstacles). However, we know that light can go around
obstacles; silly Issac! Newton also had a difficult time explaining what
makes light a certain __________.
A Dutch scientist __________________ ______________ led the charge
that light is a ________. H____________ noticed diffraction in light, which
seemed to back up his theory that light is a wave. Huygens also had a
difficult time explaining the difference between different ____________ of
light.
Huygens “knew” that if he (or someone else) could just show that light
____________________, then it could be “proven” that light is a wave. In
1801, Thomas __________, did his famous ____________-________
experiment, showing how light does __________________. For the
remainder of the century, those in the know said that light is a wave.
Now, we say that light has a d______ nature; sometimes it acts like a
________________, and sometimes it acts like a ________, although it ____
neither a particle nor a wave.
The Speed of Light
The ancients were unsure if light traveled
i____________________________, or if it had a time d________. Many
tried to measure the speed of light, but measuring the ________ over which
it traveled proved to be too hard.
The first demonstration that light travels at a finite speed was supplied by
Danish astronomer O________ R__________ about 1675. He noticed
discrepancies in the period of ____, one of _______________’s moons.
This discrepancy was explained by Huygens as the extra time it took for
light to travel across E________’s o________.
The most famous experiment to measure the speed of light was that done by
Albert M________________ in 1880. He used an o________________
____________ that spun to measure the time light traveled to a distant
mirror and back. For his effort, he won the __________ __________, the
first one by an ________________.
A __________ ________ is the distance light travels in ______ ________.
The closest star is ________ light years away. Since we know that light
travels ______________ m/s, that is very, very far away.
Electromagnetic Waves
Light is energy that is emitted by a______________________
e______________ c____________. Since this wave is partially
e______________ and partially m______________, it is called an
______________________________ wave.
Electromagnetic waves are arranged in order of frequency and wavelength
on the electromagnetic ________________. The lowest frequency (or
highest ____________________) are the __________ waves. Just above
them are the m__________________, and then i______________. Next
comes the ______________ spectrum, which includes all the colors we can
see, arranged from ________ (longest wavelength) to ____________
(shortest wavelength). This visible spectrum’s wavelengths range from
________ ____ for red light to about ________ _____ for violet light.
Even shorter wavelength than that are the ______________________ and
__-rays. Finally, __________-rays have an extremely short wavelength, and
consequently, a very ________ frequency.
Reflection and Refraction
At a boundary or __________________, usually part of a wave is
__________________ and part passes into the second medium. According
to the law of reflection, the angle of _________________ equals the angle
of ____________________.
A plane mirror forms a ______________ image of an object; the image
appears to be as far in back of the mirror as the object is in front of the
mirror and is the same size as the object.
In ____________________, a wave reaches the boundary between two
media and changes direction as it passes into the second medium.
Refraction is caused by a difference in __________ of the wave in the two
media.
In __________ ________________ ____________________ , an incident
light wave on a boundary is at a __________ enough angle (talking about
the angle of incidence), so that none of the wave can be
__________________, so only ____________________ occurs.
Convex mirrors always form images that are ______________,
______________, and ______________.
Concave mirrors can form different images. If an object is beyond the focal
point, the image formed will be ________ (it can be put onto a screen
because actual light rays are producing it) and ________________. When
the object is within the focal point (between the mirror and the focal point),
the image is _______________, _______________, and ______________
(not formed by actual light rays-only formed in the mind).
Any lens refracts parallel light rays so they cross or appear to cross at a
__________ __________. A converging lens is ______________ in the
middle than at the edges, and a diverging lens is ______________ in the
middle than at the edges.
A converging lens forms virtual, enlarged images when the object is within
one __________ ____________ of the lens. A converging lens forms
________ images when the object is beyond one focal length of the lens.
A __________________ lens always produces virtual, reduced images.
Light and Transparent Materials
Materials can be either ______________________,
______________________, or ____________, depending on how they
allow light to pass through them. If an object is _____________________,
light can pass through and as it does, photons stay in their original
a____________________, allowing a picture to come through.
Consequently, it is possible to ________ through.
Photons can come through so easily because the frequency of the light does
not match the ______________ __________________ of the glass atom.
Because of the different frequency, glass atoms hold onto the photon’s
____________ for a very short while.
It is important to remember that when a photon hits a glass atom, the photon
is a______________ by the atom. One of the atom’s e________________
gets ex__________ to a higher e__________ l________. This is a short
lived state, however, and soon the electron returns to its original state,
releasing a p__________ of energy. Importantly, the emitted photon is not
the same photon as the original photon. Same e___________, but different
p__________.
Photons in the u___________________ and i______________ range more
closely match the natural frequency of glass. As a result, glass holds onto
energy in this range, and glass becomes o__________ to ultraviolet and
infrared light.
T____________________ materials are similar to transparent materials with
one big difference: you cannot _______ _____________ them. When a
photon hits a translucent material, the photon is absorbed as in a transparent
material, but instead of a speedy re-________________, the translucent
material atom will hold onto the energy ____________. This longer time
delay can result in re-emission in a different d________________ than
originally. Photons get all mixed up, resulting in their picture message being
lost. Rather than seeing a picture, we only see l________.
27.5 Opaque Materials
Materials that absorb light without re-______________ are called
o__________. Light photons match the n___________ frequency of the
opaque material atoms, and r________________ occurs. Energy is not reemitted. Instead, it is turned into ________.
Metals are also opaque, but they are shiny. This results from the f______
electrons metal atoms have. They can absorb photons and re-emit them back
the way they came. This gives metals their __________ appearance.
Wet materials appear dark because water is ______________________.
When incident light his dry materials, the light is quickly
__________________. When incident light hits wet materials, the light can
pass through the water and bounce around for awhile. When it is finally
reflected back, the numerous bounces each allowed
some____________________, and the light that is finally reflected to your
eye is less intense.
Polarization
A transverse wave is __________________ if the medium is only vibrating
in _______ direction. In contrast, non-polarized waves vibrate in ________
directions. A single vibrating electron emits an electromagnetic wave that is
polarized, but an incandescent light bulb emits electromagnetic waves that
are not polarized, because electrons are moving in ____________
directions.
A polarizing filter contains long, light-a_____________ molecules that only
permit light vibration in one direction to pass through.
A pair of glasses made with polarizing lenses can be extremely useful to
someone who wants to eliminate g________, which is produced when light
hits a flat surface. When light hits a flat surface, the light becomes
__________________. The reflected light is oriented p_____________ to
the surface, while the transmitted light is oriented
p_____________________ to the surface.
See
Light
Particles
Plato
Socrates
Euclid
Streamers
Filaments
Exited
Dark-room hypothesis
Newton
Particles
Reflection
Diffract
Color
Christian Huygens
Wave
Huygens
Colors
Interferes
Young
Double-slit
Interfere
Dual
Particle
Wave
IS
Instantaneously
Delay
Time
Olaus Roemer
Io
Jupiter
Earth’s orbit
Michelson
Octagonal mirror
Nobel Prize
American
Light-year
One year
Four
3.0 x 108
accelerating
electric charges
electric
magnetic
electromagnetic
spectrum
wavelength
radio
microwaves
infrared
visible
red
violet
700 nm
400 nm
ultraviolet
X
Gamma (γ)
High
Interface
Reflected
Incidence
Reflection
Virtual
Refraction
Speed
Total internal reflection
Great
Refracted
Reflection
Virtual
Upright
Reduced
Real
Inverted
Enlarged
Upright
Virtual
Focal point
Thicker
Thinner
Focal length
Real
Diverging
Transparent
Translucent
Opaque
Transparent
Orientation
See
Natural frequency
Energy
Absorbed
Electrons
Excited
Energy level
Photon
Energy
Photon
Ultraviolet
Infrared
Opaque
Translucent
See through
Re-emission
Longer
Direction
Light
Emitting
Opaque
Natural
Resonance
Heat
Free
Shiny
Transparent
Reflected
absorption
polarized
one
all
all
absorbing
glare
polarized
parallel
perpendicular