Chapter 18 3c531n

Chapter 18: Electromagnetic Spectrum & Light

18.1: Electromagnetic Waves Electromagnetic Waves- (EM) transverse waves consisting of changing _______________________ and changing _______________________________________. Electromagnetic Waves: Can carry ______________ from one place to another Produced by constantly changing fields Magnetic and electric fields travel at ________________________ to each other Electromagnetic waves are produced when an electric charge _________________________________. As fields regenerate, their energy travels in the form of a _________________. Unlike mechanical waves, EM waves ____________________________________________. EM waves can travel through a _______________________ (or empty space) or matter. _________________________________________- the transfer of energy by electromagnetic waves traveling through matter or across space. Speed of Light Analogy Scientists have discovered that light and all electromagnetic waves travel at the same speed when in a vacuum  __________________________ m/s! Consider driving non-stop at 60 mph from NYC to San Francisco. This trip would take you ~50 hours Light travels this distance in less than 0.02 second!!! •

Speed of EM wave = wavelength x frequency

Wavelength is ______________________________________ to frequency As the wavelength _______________________, the frequency ___________________.

Differences between EM Waves: Even though all EM waves travel at the same speed, it does not mean they are all the same! EM waves vary in __________________ and ___________________. •

Math Skills p. 535 1-3

•

Section 18.1 Assessment Questions 1-10 p. 538

•

Handout on Frequency, wavelength, and speed problems

•

18-2: The EM Spectrum In 1800, _________________________ used a prism to separate the wavelengths present in sunlight. He produced a band of color: ____________________________________________

•

______________________________________________________________________ EM Spectrum –

The full range of frequencies of electromagnetic radiation is called the ______________________________ which includes the following parts: radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays.

Each kind of wave is characterized by a range of _________________ and ______________________. ___________________________________ have the ________________________________ in the EM spectrum, from 1mm to 1000’s of km. They also have the ______________________________, 300,000 mHz or less. Ex. used in radio, TV, microwaves, and radar In a radio studio, music and voices are changed into electronic signals that are carried by radio waves.

AM radio stations broadcast by _____________________________________, the amplitude of the wave is varied FM radio stations broadcast by ______________________________________, the frequency of the wave is varied A station is lost when its signal becomes too weak to detect, an FM station is more likely to be lost because FM signals do not travel as far Radio Waves also include the application of:

a. Television-Radio waves also carry signals for TV, including the information for pictures b. Microwaves c. Radar (___________________________________________) Short bursts of radio waves that reflect off objects they encounter and bounce back, being detected by a radio receiver Infrared Radiation: Infrared waves have higher frequencies than radio and wavelengths that vary from about 1mm to 750nm Used as a source of heat and to discover areas of heat differences _____________________________ to our eye Warmer objects give off more infrared than cooler, a device called a thermograph create thermograms (color-coded picture) that show temperature variation ________________________________ can be used to find places where a building loses heat, search and rescue teams use infrared cameras to locate victims Visible Light: The visible part of the EM spectrum is ____________________________________________________. Each color of the visible spectrum corresponds to a specific frequency and wavelength (ROYGBIV) Ultraviolet (UV) Rays: The wavelengths of ultraviolet rays very from 400nm to about 4nm, and higher frequencies than violet light. In moderation, UV rays help your ______________________________________ Excessive exposure can cause ___________________________________

Used to ______________________________ and Plant nurseries use UV to help plants to grow during winter Gamma Rays: Gamma rays have the ___________________________ about 0.005nm or less, and have the _________________________ and therefore the ___________________________________ ___________________________________________________________________________ Used in the medical field to ___________________________________, in brain scans, and in industrial situations such as inspecting pipelines for sign of damage Overexposure can be deadly Gamma Rays & Radiotherapy The normal cells receive a lower dose of gamma radiation than the cancer cells, where all the rays meet. ___________________________________ aims to kill the cancer cells while doing as little damage as possible to healthy normal cells. •

Data Analysis: How Long Does an Antenna Need to Be? P. 542

•

Quick Lab Evaluating Sunscreen p. 544

•

Section 18.2 Assessment Questions 1-7 and Writing in Science p. 545

18.3 Behavior of Light How light behaves when it strikes an object depends on many factors…including the material it is made of. Materials can be: 1._______________________ 2._______________________ 3._________________________

Transparent: _______________________________________________________________ Most light is able to through Examples: water, windows

Translucent: ___________________________________________________________________ ______________________________________________________________________________. Scatters Light Examples: some types of jello, certain bars of soap, frosty windows Opaque: ______________________________________________________________________t. NO light is able to through Examples: fruit, wooden table, metal desk Interactions of Light When light encounters matter, some or all of the energy in the light can be transferred to the matter. And just as light can affect matter, matter can affect light. When light strikes a new medium, the light can be: 1._____________________________________ 2.______________________________________ 3._______________________________________ Reflection: •

When you look in a mirror, you see a clear image of yourself. –

•

•

An _________________ is a copy of an object formed by reflected (or refracted) waves of light.

Two types of reflection: –

__________________ Reflection

–

_______________________ Reflection

_________________________________: occurs when parallel light waves strike a surface and reflect all in the same direction

Occurs when light hits a smooth, polished surface Mirrors or surface of a still body of water (page 547, figure 18)

______________________________________: occurs when parallel light waves strike a rough, uneven surface, and reflect in many different directions – Paper has a rough surface, (page 547, figure 18) – Rough surfaces causes diffuse reflection of the light that shines on it Reflection occurs because there is no transmission of light (light is not able to through to the new material) However, when light is transmitted different things can happen. Light can be:

1. ________________________ 2. ________________________ 3. ________________________ Refraction: ability of light to refract, or ___________________________________________ ___________________________________________________________________________. –

•

Two easily observable examples that occur when light travels from air into water: Underwater objects appear closer and larger than they really are and can make an object such as a skewer (or pencil) appear to break at the surface of the water (page 548, figure 19)

Refraction can sometimes cause a mirage.

Mirage: a _______________________________________________________________. Mirages occur because light travels faster in hot air than in cooler, dense air –

On a sunny day, air tends to be hotter just above the surface of a road than higher up

–

Mirages also form this way above the hot sand in deserts

Polarization Light is an EM Wave  EM waves vibrate in TWO planes Light waves that vibrate in only one plane is called __________________________________. –

Polarizing filters transmit light waves that vibrate in only one direction or plane (page 548, figure 20)

–

Unpolarized light vibrates in ALL directions

Scattering ___________________________________ contains many molecules and other tiny particles. These particles can ______________________________________. Scattering: light is redirected as it es through a medium (page 549, figure 21)

•

Scattering effect reddens the sun at sunset and sunrise

Small particles in the atmosphere _____________________________________________________ _________________________________________________________________________________ By the time the sunlight reaches your eyes, most of the blue and even some of the green and yellow have been scattered Most of what remains for your eyes to detect are the longer wavelengths of light, orange and red •

Do why is the Sky Blue Activity

•

Do Build Science Skills p. 548 using polarizing filters

•

Section 18.3 1-7 p. 549

18.4 Color How does a prism separate white light into a rainbow? Light enters a new medium (the prism) and is _________________. The __________________________________________________________ than the longer wavelengths and the colors separate. Draw a picture of how the light would look leaving a prism. (Color code it)

Describe how a rainbow forms. Water droplets in the air act like ____________________________________________________________________________________ Explain what the color of an object depends on. The color of any object depends on ________________ _____________________________________________________________________________________ What are the primary colors of light? _______________________________________________ What are the secondary colors of light? _____________________________________________

What are complementary colors of light? Any two colors of light that combine to form white light. (one primary color and one secondary color of light) Give examples of two sets of complementary colors of light. 1. Magenta + green 2. yellow + blue What are the primary colors of pigment? ___________________________________________________ What are the secondary colors of pigment?__________________________________________________ What are complementary colors of pigments? Any two colors that combine to make black (secondary color + primary color) Give examples of two sets of complementary colors of pigments. 1. Green + magenta 2. red + cyan 18.5: Sources of Light Incandescent Light: When electrons flow through the filament of an incandescent light bulb, the _____________________ ________________________________________________________________________________. Common light bulbs. mercury atoms to emit ultraviolet rays. These rays cause the phosphorcoating to emit light. Fluorescent Light: Emit light by causing a phosphor (usually zinc sulfide) to steadily emit photons. Electrodes in a fluorescent bulb emit electrons that cause the mercury atoms to emit ultraviolet rays. These rays cause the phosphor coating to emit light Neon Light: Light is emitted when electrons move through a gas or a mixture of gases inside the tube. Advertising signs Laser Light:

Coherent lights in which waves have the same wavelength, and the crests and troughs are lined up. This beam doesn’t spread out significantly from its source, so it has a relatively constant intensity allowing the energy it carries to be focused on a small area. Read bar codes, surgeries, DVD players Sodium Vapor Light: As electric current es through a sodium-vapor bulb, it ____________________________________. The mixture warms up and the heat causes the sodium to change from a solid into a gas. These are used to light streets and parking lots. Tungsten-Halogen Light: Inside a tungsten-halogen bulb, electrons flow through a tungsten filament. The filament gets hot and emits light. Section 5 Assessment Questions 1-5 p. 562 Exploration Lab: Mixing colors p. 563