LIGHT

Types of Light Waves

• Light waves are grouped by different frequencies and wavelengths.

• These are the different types of electromagnetic waves.

Electromagnetic Spectrum

• Video

Electromagnetic Spectrum

• Energy that is given off by electrons that moves in waves.

Look at your pictures and answer the questions:

• Which ELECTROMAGNETIC WAVE has the most energy? The least?

• Which ELECTROMAGNETIC WAVE has the longest wavelength? The shortest?

• As frequency increases, what happens to energy?

• As frequency increases, what happens to wavelength?

• As the wavelength increases, what happens to the frequency of the waves?

• Radio waves• Microwaves• Infrared Waves• Visible Light Waves• Ultraviolet Waves• X-Ray Waves• Gamma Waves

Radio Waves

• Radio waves are used for radio broadcasts, amateur radio, digital television, and cell phones.

Microwaves

• Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn.

Infrared Waves

• Infrared waves are used to heat food at restaurants, by police scanners, in your remote control.

Ultraviolet Waves

• UV Waves are used in tanning and in sterilization of equipment.

X-Ray Waves

• X-Rays are so strong, they can go right through you!

Gamma Waves

• Gamma rays and X-Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is called radio-therapy or radiation.

LIGHT WAVES- Visible Light

• VISIBLE LIGHT is a form of electromagnetic energy that we can see.

Visible Light

White Light

• Sunlight is white light.• White light = every color of light

PRISM

• A prism REFRACTS white light into all its colors!

What color light is refracted the most?

Visible Spectrum

• Visible Spectrum = the colors that you can see.• All the colors of the rainbow

Visible Spectrum

Red (longest wavelength)OrangeYellowGreenBlueIndigoViolet (shortest wavelength)

                                                             

How does light travel?

• Light is made up of bunches of energy called photons.

• Light travels in waves.• Light is an example of a transverse wave.

Speed of light

• Light travels fastest through empty spaces.• Light waves slow down or get stopped by matter.

In air at room temperature, speed travels at:v = 300 000 km/s = 3 X 108m/s

Remember, sound travels at 344 m/s, so light is about 1,000,000 times faster!

Light & Optics

How do I see Light?

Materials that light hits can be:

• Opaque- (Solid) – Does not let light pass through.– A door is opaque.

• Transparent- (See-through) – Lets light pass through.– A window is transparent.

• Translucent- (Not clear) – Lets some light pass through. – A glass of lemonade is translucent.

When light hits a material, the light may:

• Reflect: Bounce off• Refract: Bend• Get Absorbed

Reflection

Law of Reflection

• The angle the light ray hits the mirror equals the angle it bounces off.

• The angle of incidence equals the angle of reflection.

The Law of Reflection

• Diffusion = the breaking up of light

Think about roads…

Look at the curved mirrors.

What do you observe about the reflection?

Sound waves that hit this would all go to the microphone.

What color light is in the middle?

Refraction

• Waves bend when they pass into a different medium.

• This happens because the speed of light changes.

Refraction explains how lenses work:

Your eyes have color sensors.

• Thousands of rods & cones in your eye tell your brain how much red, green and blue light hits your eye.

How do we see colors?

                                                   

When ALL of the colors of light combine…

White light is produced.

                

The Sun gives off "white" light, a mixture of all the colors in the spectrum. The object looks WHITE because an equal mixture of RED, BLUE, and GREEN light is reflected off the object and interpreted by our eyes and brain as WHITE.

You can use a FILTER to absorb a color of light.

Your TV works using little pixels that look like this:

Any color can be made from a combination of these three colors of light.

When colors of pigment, (or paint) combine:

Colors affect our mood!

• Red = Stimulating• Yellow = Excitement• Blue = Calming• Which would you eat?

Colorblindness

• Some people have trouble telling the difference between colors.

• Their rods and cones do not detect differences.

The last test is the easiest to use.

• A person with normal color vision will see a “5” in the dot pattern.

• A person with Red/Green color blindness (the most common) will see a “2” revealed in the dots.

Sometimes your eyes get tired!

• Your rods & cones get used to what they see and it takes them some time to go back to normal.

Sometimes, your eyes play tricks on you!

Which guy is the tallest?

How many shelves are here?

Are these bricks in straight rows?

Look at the center and move closer to the screen!

Are the long lines parallel?

Look at the center & move your head.

Are the purple lines parallel?

Curved or straight?