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# How Light Transmit, Reflect, Absorb and Refract Through Different Materials

By: Kaley
by

## Queenie Zhao

on 2 February 2011

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#### Transcript of How Light Transmit, Reflect, Absorb and Refract Through Different Materials

How Light Works light transmission Reflection
Some materials may contain free electrons that can jump from one atom to another atom within the material, so when the electrons in this type of
material absorb energy from incoming light, they don't pass that energy ontoother atoms.

These electrons just vibrate and then send the energy back out of the object exactly like it came in, like it has the same frequency.

The light doesn't penetrate the material deeply.

Basically the object appears shiny like most metals and sometimes glass.

The wave of light that came out of the object comes out at an equal angle to what it came in.

This is called the Law Of Reflectance, the angle of incidence (the incoming light ray) equals the angle of reflection (the outgoing light ray).

Scattering is just reflection but on a rough surface.

The incoming light waves get reflected every which way because the surface is uneven.

Paper is a good example for this, when you look at paper under a microscope you can see that it's rough.

Because it's rough the light reflects everywhere, which
helps when you write because you can read the letters you write on the paper despite what angle you're looking at it from. Transmission
The frequency of the light is either way higher or way lower than the frequency in the material vibrate, so the electrons will not capture the energy of the light, so the light will pass through the material, unchanged.

Most materials are transparent to some frequencies, but others are not.

AKA

High frequency light light X-Rays and Gamma Rays will pass through ordinary glass but low frequency light like Ultraviolet and Infrared light won't. Bibliography:
http://www.howstuffworks.com/light.htm/printable
http://www.physicsclassroom.com/class/light/u12l2c.cfm
http://www.physicsclassroom.com/class/refrn/u14l2a.cfm
http://www.rpi.edu/dept/phys/ScIT/InformationTransfer/reflrefr/rr_content/reflection_10.html Refraction
Refraction happens when the energy of the incoming light matches the natural vibration frequency of the electrons in the material.

Because of this, the light waves travel deeply into the material, and causes small vibrations in the electrons.

These electrons pass the vibrations onto the atoms in the material, which then send out light waves of the same frequency as the incoming light wave. But this takes time.

The part of the wave that is inside the material slows down while the part of the wave outside of the material maintains it's original frequency.

This bends the portion of the wave inside the material toward the normal line.

The normal line is an imaginary line that is perpendicular to the surface of the object.

The amount of bending in the object depends on how much the material slows down the light wave.

Eg. diamonds wouldn't be really sparkly if they didn't slow down light waves way more than, say, water.

Here's an interesting fact, light of different frequencies/energies, will bend at slightly different angles. The End! Absorption
The absorption of light makes the object dark/opaque to the frequency of the incoming light wave.

Some materials are opaque to some frequencies of light,
but they're transparent to others.

Eg. Glass is opaque to ultraviolet light but transparent to visible light.

In absorption, the frequency of the incoming light wave is at or near the vibration frequency of the electrons in the material.

The electrons take in the energy of the light wave and start to vibrate.

What happens next depends upon how tightly the atoms hold onto their electrons.

Absorption occurs when the electrons are held tightly, and they pass the vibrations along to the nuclei of the atoms.

This makes the atoms speed up, so they collide with
other atoms in the material, and then give up as heat the energy theyacquired from the vibrations. By Kaley And Queenie Singing n1 sine theta sine 1 hey hey hey Equals N2 sine theta sine 2 hip hooray The Angle of Incidence

The angle of incidence is an angle between the ray of light and the perpendicular line to the surface, known as the normal.

To measure the angle of incidense, we just have to measure the distance between the ray of light and the perpendicular line.

We can predict the angle of incidense by knowing the distance from the ray of light to the normal, and subtract the distance by 90, becasue therefore, the perpendicular line is always 90 .

After the light ray is reflected to the normal, two things can happen; the normal will bend the light and cause it to refract, or the normal will absorb the light and cause it to refract. The Angle of Refraction

The angle of refraction happens when light bounces off different mediums than the incidence medium, which cause light to refract.

The angle of refraction is also known as Snell's law, because it's named after Willebrord Snellius.

The angle of refraction can be caused by materials such as water, air, glass and other refracting objects.

The refracted angle depends on what the refracting object is:

E.g.

Let's say the angle of incidense is at 45 in air and the refracting object is water, the angle of refraction will be 32 .

Another example is refracting materials between air and glass, the air angle will still be 45 , but the glass angle will change to 28 . The Angle of Reflection

The angle of reflection is an angle that is caused by the angle of incidense.

The light ray will reflect off the reflective normal and and cause another exactly same ray, in other words;

The Angle of Incidence = The Angle of Reflection

E.g.

In a tennis when player A hits a ball, player B will probaly (most of the time) know where the ball is going to go next, because of the law of reflection.
o o o o o o o o o Here's a video about the angle of incidence, reflection and refraction. Enjoy. In this picture, the eagle's facing the water which cause it to reflect, so the eagle would be the ray of incidence, the water would be the normal, and the eagle's reflection is the ray of reflection.
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