Light

A guide to

Electromagnetic Waves

Electromagnetic Radiation

• Electromagnetic waves are transverse waves made from electrically charged particles.

• Transfer of energy by these waves is called radiation.– No need for a medium– Travel through a vacuum or empty space– Light from the stars is one example

Electromagnetic Waves

• Electromagnetic waves are arranged on the electromagnetic spectrum by their wavelength and frequency.– Low-frequency, long wavelength---Radio waves – High-frequency, short wavelength--- gamma rays

Photons

• Radiation carries energy and has momentum.

Scientists believe that electromagnetic radiation may act like particles as well as like waves!

Albert Einstein, in 1905 hypothesized that light is composed of tiny particles.

He called these tiny bundles of radiation PHOTONS!

Electromagnetic Spectrum

• All electromagnetic waves are classified by their wavelength and their frequency on the electromagnetic spectrum.

Radio Waves

• Long wavelength, low frequency• Low photon energy• Used in Communication and Cooking:

– Radios, TV’s, Cellular Phones, Cordless phones• Modulation- the process of varying the amplitude or frequency

of radio waves by– Voice, music, video, computer information

– Highest frequency radio waves are called microwaves.• Used in cooking and communication

Radar is used to detect the echoes of radio waves from distant objects.

Infrared Radiation

• Infrared radiation indicates the presence of heat.

• Wavelength is slightly longer than that of visible light.

• Warm objects give off infrared radiation.

• Sunlight, body heat, infrared lamps are all examples of Infrared radiation.

Visible Radiation

• The only part of the electromagnetic Spectrum you can see!

• Small range on the spectrum compared to the other types of radiation.

• Visible light can cause chemical reactions to take place.

Ultraviolet Radiation

• Higher frequency than visible light

• Photons more energetic

• Ozone layer blocks most of the ultraviolet radiation from the sun.– Help the skin to produce Vitamin D– Used to kill bacteria and viruses– Too much causes skin cancer

X-Rays and Gamma Rays

• X-rays:– Shorter wavelengths and

higher frequencies than ultraviolet radiation.

– Photons have higher energy and carry more penetrating power.

– Passes through some materials and absorbed by others.

– Used to Scan luggage at airport

• Gamma Rays– Highest frequency

– Most penetrating

– Emitted from the nuclei of radioactive atoms

– Can kill cancer cells

Light

• The type of material determines the amount of light it absorbs or reflects– Opaque materials absorb or reflect light so you

cannot see through them.• Heavy dark curtains on a window

– Transparent materials allow light to pass through, you can see clearly through them

• Glass windows

– Translucent materials allow some light to pass through, but you cannot see through them clearly

• Sheer curtains, frosted glass, waxed paper

Color

• White light is made up of the colors of the spectrum.

How you see the colors of light

• An object appears to be a certain color because that is the color of the light spectrum it reflects.

• An object appears white because it reflects all the colors of the light spectrum.

• An object appears black because it absorbs all the colors of the light spectrum and reflects little or no light.

How colors of light are seen

• Primary Colors of light– Red Green Blue

Photoreceptors1.Cones: 3 Types

A. Red Cones Absorb Red and Yellow LightB. Green Cones Absorb Yellow and Green LightC. Blue Cones Absorb Blue and Violet Light

2. Rods:Sensitive to dim light and are used for night vision

Color---Seeing the light

• Check your vision for color blindness.– 8% of men, .5% of women suffer.

• What numbers do you see??

• An inherited condition where cones malfunction.

Pigments

• A pigment is a material that absorbs some colors and reflects others.– Used by artists to make

colors of paint.– Three primary pigments

• Cyan, magenta,yellow

– Color of pigment depends on the light it reflects

Battle of the Bulbs

• Incandescent Lighting– Thin wire of tungsten (W)

– Gets very hot!

– Gives off light

– 80% of the energy given off is heat.

• Fluorescent Lighting– Filled with gas, Argon

– Coated with phosphors

• Give off visible light when they absorb UV radiation.

– No excessive heat given off

– Use 1/5 the electricity

– Last longer

– Can confuse your TV and VCR