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II. Wave Properties

A. Amplitude—the measure of how high the crests are or how deep the troughs are; or the distance between the particles in a compression and rarefaction

B. Wavelength—distance from the top of one crest to the top of the next crest or from the bottom of one trough to the bottom of the next trough; or the distance from compression to compression or rarefaction to rarefaction

C. Frequency—number of wavelengths passing a given point per second

1. Longer wavelengths result in smaller frequencies.

2. Larger frequencies result in shorter wavelengths.

3. Color and pitch result from wavelengths and frequencies of light and sound.

D. Wave speed—how fast a wave travels through a medium

1. Mechanical waves travel faster in a medium in which atoms are closer together.

2. Electromagnetic waves travel faster in a medium with fewer atoms in it.

A. Sound is produced by vibrations.

B. A sound wave is a compressional wave in which air molecules move back and forth along the direction the sound wave is moving.

1. A sound wave is created by a series of compressions and rarefactions.

a. A compression is a region of higher density air molecules.

b. A region of lower density air molecules is called a rarefaction.

2. Sound waves can be described by their wavelength and frequency.

C. Sound waves can travel through various materials at different speeds.

1. Sound travels fastest through solids, and slowest through gases.

2. Sound travels faster in a warmer substance.

D. Loudness is the human perception of how much energy a sound wave carries.

1. Sound waves with greater amplitude carry more energy and sound louder.

2. The decibel (db) scale describes the energy carried by sound waves.

E. Pitch—how high or low a sound seems

1. Pitch is related to frequency and wavelength; the higher the frequency and the shorter the wavelength, the higher the pitch.

2. The length and thickness of vocal cords help determine the pitch of the human voice.

a. Shorter, thinner chords vibrate at higher frequencies than longer or thicker ones.

b. People can vary their vocal pitch within a limited range by using the muscles in the throat to stretch the cords.

F. Echo—a sound wave reflected off of a hard surface

1. The delay in reflection of sound is used to measure distances such as in sonar systems which map the ocean floor and other undersea features.

2. Some animals use echolocation to navigate and hunt.

IV. The Nature of Electromagnetic Waves

A. Electromagnetic waves, produced by charged particles in motion, travel through space, transferring energy.

B. An electromagnetic wave is composed of two force fields—an electric field and a magnetic field.

1. Earth’s gravity field exerts a force on all objects and extends out into space.

2. A magnetic field exerts a force on other magnets, causing them to line up along the direction of the magnetic field.

3. The electric field surrounding a charged particle exerts a force on all other charged particles in the field.

a. A moving charged particle is surrounded by an electric field and a magnetic field.

b. As a charged particle moves up and down, it produces an electromagnetic wave.

C. Electromagnetic waves have a wavelength and a frequency.

1. One complete vibration of the charged particle up and down creates one wavelength in an electromagnetic wave.

2. The number of wavelengths that pass by a point in 1 second is the frequency of the electromagnetic wave.

D. Radiant energy—energy carried by an electromagnetic wave

1. The amount of energy carried by an electromagnetic wave is determined by its frequency.

2. The higher the frequency, the more energy the electromagnetic wave has.

E. Electromagnetic waves travel at the speed of light, 300,000 km/s, in space.

A. Electromagnetic waves have a series of different frequencies and wavelengths called the electromagnetic spectrum.

1. For waves that travel with the same speed, wavelength increases as frequency decreases.

2. Radiant energy decreases as wavelength increases.

B. Radio waves have the lowest frequency and carry the least energy.

1. AM and FM radio signals and television signals are types of radio waves; they can be sent with radio waves using a transmitting and receiving antenna.

a. One way to make radio waves is to make electrons vibrate up and down in a piece of metal called an antenna.

b. The radio waves from the transmitting antenna can cause electrons in another piece of metal, such as a receiving antenna, to move up and down, creating an alternating current.

c. The current can be used to produce sound from a loudspeaker, allowing for the transmission of music, television shows, and telephone signals.

2.Microwaves have a higher frequency and shorter wavelength than radio waves; they are used for some phone calls and to heat food.

3. Radar uses electromagnetic waves to locate objects by measuring the time it takes for the waves to reach the object, be reflected, and return.

C. Infrared waves have wavelengths between one thousandth and 0.7 millionths of a meter and feel warm or hot.

1. Infrared detectors sense objects that are warmer or colder than their environment; TV and VCR remote controls also use infrared waves.

2. Some animals, such as piranhas and rattlesnakes, can detect infrared waves, which helps them find prey.

D. Visible light has wavelengths between 0.7 and 0.4 millionths of a meter.

1.What you see as different colors are electromagnetic waves of different wavelengths.

2. Red light has the longest wavelength (lowest frequency); blue light has the shortest wavelength (highest frequency).

E. Ultraviolet radiation is higher in frequency and has shorter wavelengths than visible light.

1. Too much exposure to ultraviolet radiation from the Sun can cause sunburn and other health problems.

2. Since ultraviolet radiation can kill cells, it is sometimes used to sterilize equipment.

3. The ozone layer in Earth’s upper atmosphere helps protect the surface by absorbing much of the Sun’s ultraviolet radiation.

F. X rays and gamma rays, with even higher frequencies than ultraviolet rays, can go right through skin and muscles.

1. Too much exposure to X rays or gamma rays can damage or kill cells.

2. X rays are useful in medical diagnosis if used with appropriate precautions.

3. Gamma rays, which have the highest frequency, can be used to treat cancerous tumors and to kill bacteria in food.

G. Some astronomical objects emit no visible light but are known through infrared and radio images; satellite observations outside Earth’s atmosphere help scientists study space at wavelengths that do not reach Earth’s surface.

VI. Using Electromagnetic Waves

A. The world is becoming increasingly connected through the use of electromagnetic waves in telecommunication.

B. Radio waves are the electromagnetic wave of choice for most telecommunication technology.

1. The assigned frequency for a TV or radio station signal wave is its carrier wave.

2. In amplitude modulation, the amplitude of the carrier wave is changed to transmit information; the frequency is not changed.

3. In frequency modulation, the frequency of the carrier wave is changed.

C. Telephones can convert sound waves to an electrical signal that can be converted to radio waves, microwaves, or light waves. Receivers convert the transmission back into an electric signal, and a speaker changes the electric signal into a sound wave.

1. Cordless phones and cellular phones use radio waves to transmit signals.

2. Pagers use electromagnetic signals from a base station.

D. Communication satellites enable radio signals to be sent from one part of Earth  to another.

E. The Global Positioning System consists of satellites, ground-based stations, and portable units with receivers used to help locate objects on Earth.