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 re-emitted. 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