Mr. Bouyer

Day 1 | Day 2 | Day 3 | Lab 1 | Lab 2 | Vocabulary Test | Energy WebQuiz

Light Excited atoms Electromagnetic spectrum Photoelectric effect Transparent Translucent Opaque Index of refraction Prism Incandescent Fluorescent	Neon Polarized Laser Primary colors Complementary colors Pigment Mirror Plane Virtual image Concave Real image Convex	Lens Focal point Hologram Fiber optics Pupil Iris Retina Rods Cones Nearsighted Farsighted Flicker-fusion

Light

Excited atoms:  (ps lab 134)
• Electrons in an energy level have a specific amount of energy.
• If an electron absorbs energy, it is bumped to a higher energy level.
• This produces an unstable, or "excited" atom.
• Atoms do not like to be excited. The electron will loose the extra energy by giving off a photon, allowing it to fall back to its original energy level.
• Photon - a packet of energy released by an excited electron.

The frames of this animation of an atom producing light represent:
1. The atom is normal.
2. The electron absorbs a packet of energy.
3. Because of the excess energy, the electron must move to a higher energy level.
4. The atom is now "excited".
5. The electron immediately drops back to its normal energy level.
6. To do this, the electron releases the excess energy in the form of a photon.
7. Light is produced.

Electromagnetic spectrum:

• An arrangement of all electromagnetic waves by decreasing wavelength, and therefore increasing frequency.

Light behaves like a wave -
The wave theory of light explains most of the properties and behavior of light very well. However, this theory can no longer explain all the things we have observed about light.
Light behaves like a particle -
High energy light will produce an electric current when it strikes a metal plate, while Low energy light will not. If light was a continuous wave, even the energy from lowly "red" light would eventually be absorbed and cause some electron movement. This does not happen.
Speed of light:

In a vacuum, light travels at a speed of 186,000 miles per second. In a vacuum, light travels at a speed of 300,000 kilometers per second. In a vacuum, light travels at a speed of 3 X 106 meters per second. The speed of light decreases as the density of its medium increases.

Find things thatslow light down.  

Photoelectric effect: the production of electrons by the photons of light.

• A high-energy "violet" photon can knock a single electron out of its atom.
• A low-energy "red" photon cannot.
• This can be explained only if light is made up of particles.

Test Your Concept Understanding: Do you believe light is a particle or a wave? Give the reasons for your belief. Learn about the discovery of the electromagnetic spectrum. Who is the person credited with first thinking of light as waves? Even Galileo Galileii failed to determine the speed of light because it was much faster than he thought possible. Who was the first to measure the speed of light and what did he use to do it? At 186,000 miles per second, how many times could light travel around the world in one second? What was Albert Einstein awarded the Nobel Prize for in 1921?

1. Light can be transmitted - Light passes through the substance it strikes.
   Transparent - Light passes through so you can see clearly.
   Translucent - Light passes through but is scattered so you cannot see clearly.
   Opaque - Light does not pass through.
2. Light can be absorbed - Light passes into the substance and is held there.
3. Light can be reflected - Light strikes a substance and bounces back.

• The comparison of the speed of light in air with the speed of light in a certain material.
• The larger the index of refraction, the more light rays are bent.
• Prism - An object that forms a spectrum as light passes through it.

Primary Colors: The three colors of light that can be mixed to produce white light.

Primary colors of light

Secondary colors of light

Complementary colors: Any two colors of light that combine to form white light.

Pigments: Chemicals that reflect certain wavelengths of light and absorb the others.

The three primary colors of pigments are the "complements" of the three primary colors of light. When the three primary pigment colors are added, you get black instead of white. Your textbook has a good color chart showing this.

Mix somecolors.

Homework Assignment 332:
This assignment must be turned in by the beginning of class tomorrow to receive credit.
Scoring criteria

1. What three things can happen when light strikes an object?

2. Look at the west wall (not the windows) in the science room. What type of reflecting surface is that wall?

3. Answer the following questions about rainbows.
   1. Three things are needed to see a rainbow: an observer, rain, and sunlight. Describe the way these three must be positioned for a rainbow to be seen.
   2. We all know that it is the raindrops that are refracting the sunlight. How many colors can be observed from a single raindrop?
   3. What color is always at the top of a primary rainbow?
   4. What color is always at the bottom of a primary rainbow?
   5. List the two ways that secondary rainbows appear different from primary rainbows?

4. The following questions relate to this picture of a prism.
   1. Describe the two places in this picture where "reflection" is demonstrated.
   2. Which color of light is bent the most?
   3. The color of light that is bent the most has the shortest wavelength. How does this cause it to be bent the most?

When everyone at your table has completed the assignment, ask your facilitator for a prism and a flashlight. Use these to project a visible spectrum onto the wall. How does the arrangement of the colors in the prism compare with the arrangement of colors in a rainbow?

Hologram A three-dimensional image produced with laser light.

Fiber optics The transfer of light through long, thin, flexible optical fibers. These fibers are rapidly replacing wires in communication systems because of the capacity they have to carry large amounts of information.

How you see:

• Pupil - The opening through which light enters the eye.
• Iris - The colored area around the pupil that controls the amount of light entering the eye.
• Lens - Focuses light rays on the retina.
• Retina - The lining of the back of the eye containing nerves that transfer the image to the brain.
• Rods - Nerve cells that are sensitive to light and dark.
• Cones - Nerve cells that are sensitive to a particular primary color.

Flicker-fusion: the number of frames per second at which sequential images are no longer seen as separate. Humans can distinguish from 16 to 24 flickers per second. Motion pictures show about 30 still frames per second. A honey bee can see about 265 flickers per second.

Test Your Concept Understanding: You watch a movie shown at 10 frames per second. What do you see? One of your classmates is wearing a red shirt. Why is the shirt red? Find out about fireworks. Yellow is the most common color of fireworks. The atoms of which element are used to produce yellow? Blue is the color least often used in fireworks. The atoms of which element are used to produce blue? A deep forest green color is almost impossible to produce in fireworks. Using one sentence, explain why this is true.

Research Links:

• Rainbows - University of Minnesota
• All About Color - Color Matters
• Causes of Color - Web Exhibits

Red has the longest wavelength of all colors of light.

"Neon lights" producing colors other than red are made of an inert gas other than neon.

Cones of your eyes can only recognize the three primary colors, red, yellow, and blue.
Each cone in the eye can only recognize one of the colors, so we have three types of cones in our eyes.