E-M Spectrum and Waves

Prentice Hall Chapter 18

Chapter Assignments

• Workbook and E-M Spectrum Activity

• Book

• Section 18.1: 535/math practice 1-3 and 538/9,10

• Section 18.2: 545/4, 5, &7

• Section 18.5: 562/3-7

• 565-67/1-10, 32-35, and FCAT practice

Review from the last chapter:• Two types of waves are:

– Regarding requiring a medium for travel• Mechanical and electromagnetic

– Electromagnetic does not require a medium

– Regarding shape of the wave• Transverse and longitudinal

– Electromagnetic waves are transverse waves

Electromagnetic (E-M) Waves (LIGHT!)

Do not require a medium through which to travel

Light travels at 3.0 x 108 m/s in a vacuum or air

Its wavelength and frequency varies according to the type of E-M wave

The full range of frequencies of electromagnetic radiation is called the electromagnetic spectrum.

Again, all of these forms move at 3.0 x 108 m/s in a vacuum (space) or air.

One type to the left of another type has a longer wavelength and a lower frequency. For instance: radio waves have a longer wavelength than infrared.

Blue light has a higher frequency than red light.

Electromagnetic waves vary in wavelength and frequency

Higher frequency

Greater energy

More penetration

Properties of E-M Waves (Light)

• Light can act as a wave or a particle• Only a very small portion of the E-M

Spectrum is visible to humans (between infrared rays and ultraviolet rays)

• Those types to the right of the visible portion are more penetrating and harmful (can be used to “look inside” or pass through objects); i.e., x rays and gamma rays

c = f c = ?

• This formula is used to determine information about light.

• Let’s say that you know the wavelength of yellow light is 600 x 10-7 m. What is its frequency? Using c = f

• f = c/ • f = 3.0 x 108 m/s / 600 x 10-7 m • f = 3/600 x 108 + 7 = 0.005 x 1015

• f = 5 x 10-3 x 1015 = 5 x 10-3+15 = 5x1012 Hz

Another problem

• Find the frequency of an electromagnetic wave in a vacuum with a wavelength of 0.02m

• f = c/ • f = 3.0 x 108 m / 0.02 m

• f = 1.5 x 1010 Hz

Assignment:

535/math practice 1-3 and 538/9,10

Behavior of Light

• Materials can affect the behavior of light– Transparent materials allow most light to pass

through– Translucent materials scatter light and makes

figures appear unclear in appearance– Opaque materials either absorb or reflect all

of the light that hits them. No light can pass through.

Interactions

• When light strikes a new medium, the light can be reflected, absorbed, or transmitted. When light is transmitted, it can be refracted, polarized, or scattered.

Reflection• When you look into a mirror, light reflects

from the mirror, and you see yourself

• Because of total internal reflection, laser light can travel inside small glass (optical) fibers and carry information

Refraction

• Bending of light as it passes from one medium into another. It makes the pencil

look broken.

Newton and Prisms• When white light passes through a prism

you see a rainbow, because of refraction:

• Different colors bend at different angles

• A rainbow is formed when water droplets in the air disperse light.

Colors of objects

• Is dependent upon what the object is made of and on the color of light that strikes the object.

• See figure 24 (page 552) in your book

Primary Colors

Primary colors of light are Red, green, blue

Primary colors of

pigment areMagenta, cyan,

and yellow

(See page 552

In your book)

Red, blue, and green light added together produce white light.

R, blue, and green are primary colors of light

Red plus green produce yellow, a secondary color

Since yellow contains both red and green, when you add yellow to blue, you get white light!

What about cyan and red?

Since cyan contains green and blue, when you add red, you get white light again!

Mixing

• Mix colors of light together, you get more light - additive process*Mix complementary colors

of light white light (blue

& yellow or green & magenta)

*Complementary colors

are opposite each other

in the color wheel.

• Mix colors of pigment together, you get less light (it’s absorbed) - subtractive process.

The primary colors

of pigment are the

secondary colors

of light!

Assignments:

• Section 18.2: 545/4, 5, &7

• Section 18.5: 562/3-7

• 565-67/1-10, 32-35, and FCAT practice

Other tidbits about light:

• Microwaves are used to communicate between cell phones

• Light is produced in the filament of an incandescent light bulb when electrons flow through the filament

• Sodium-vapor lights are used for lighting many streets and parking lots

• Fluorescent light tubes usually contain mercury vapor (which give off invisible uv light causing phosphors to emit visible light)

Light shining on objects

• See page 552

• What an object is made of and the color of light that strikes it determine the apparent color of the object.

• In white light all colors of the object are evident

• When other colors of light shine on the object, the colors appear very different.

Laser Light

• Laser stands for Light Amplification by Stimulated Emission of Radiation.

• Laser light is coherent - all the waves have the same: wavelength, direction, and coincidental peaks. This means IT IS VERY INTENSE & CAN BE HARMFUL!!!

Light - wave or particle?

• A wave when light interferes either constructively or destructively

Light is turned “on” by constructive interference and “off” by destructive interference resulting in an interference pattern (shown at left).

Light acts as a particle when…

• Electrons are emitted from a metal caused by light striking the metal during the PHOTOELECTRIC EFFECT

Examples:

Light sensors in cameras, video cameras, automatic doors.

Newton said it acted as particles because it travels in a straight line and casts shadows.

Polarization

Only the blue waves can pass through the opening in the first card but not through the 2nd card.

Infra- and Ultra-

• Infra- means under, so infrared light is under red light (or to the left in the E-M spectrum)

• Ultra- means above, so ultraviolet light is above violet light (or to the right in the E-M spectrum)

Sources• Frames 3 & 4

• concise.britannica.com/ebc/art-70892/The-spec... • Frame 11

• www.allrefer.com/pictures/s1/r0118400-refraction • Frame 11

• hyperphysics.phy-astr.gsu.edu/.../refr2.html • Frame 12• http://www.physics.ohio-state.edu/~gilmore/images/collection/misc/prism.gif

•www.britannica.com/eb/art-90651/A-prism-sprea...

• Frame 13• www.fas.harvard.edu/.../ColorMixing06.jpg

Frame 17• hyperphysics.phy-astr.gsu.edu/.../lassol.html • Frame 18• http://abyss.uoregon.edu/~js/images/interference.gif