WAVES: Types and Properties

What is a Wave? A wave is a repeating disturbance or movement that transfers energy through matter or space

Waves transfer energy not matter. Waves can only exist as long as they have energy to carry. The Nature of Waves

Molecules of matter bump each other and pass energy from molecule to molecule. How is Energy Carried?

Mechanical waves are waves which require a medium. What are Mechanical Waves? A medium is a form of matter through which the wave travels (such as water, air, glass, etc.)

Two Kinds of Mechanical Waves: 1. Transverse Waves 2. Compressional Waves

Transverse Waves In a transverse wave the matter in the wave moves up and down at a right angle or perpendicular to the direction of the wave Examples: water waves; seismic waves; electromagnetic waves

Example: Water Wave A water wave travels horizontally as the water moves vertically up and down

Anatomy of a Seismic Wave

In a compressional wave the matter in the wave moves back and forth parallel to the direction of the wave Example: sound waves Compressional Waves

Example: Sound Waves Sound waves are mechanical, compressional waves There is NO sound in space – because there is no matter for the waves to travel through

An electromagnetic wave is a wave that can travel through a medium OR in outer space where there is no matter, or medium. Electromagnetic waves are also transverse waves Examples include: –radio waves –microwaves –infrared waves –visible light waves What are Electromagnetic Waves? – –UV waves – –X rays – –gamma rays

Wave Properties: Transverse Waves Crest: top of the wave Trough: bottom of the wave

Wavelength is the 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 (units = nm, mm, cm, m, km) Wave Properties: Transverse Waves

Amplitude: height of the wave (from the crest to the rest position; or from the trough to the rest position) Wave Properties: Transverse Waves

Wave Properties: Compressional Waves Compression: area squeezed together Rarefaction: areas spread out Wavelength: distance from the center of one compression to the center of the next compression (units = nm, mm, cm, m, km)

Frequency The frequency of a wave is the number of wavelengths that pass a given point in 1 second The unit of frequency is the hertz (Hz). Larger wavelength = smaller frequency Smaller wavelength = larger frequency

Wavelength = 25 nm – 5 nm = 20 nm (nm) What is the Wavelength??

Wavelength = 15 nm – 10 nm = 5 nm (nm) What is the Wavelength?? 25

Which has a greater Amplitude? B) A)

Which has a greater wavelength? B) A)

Which has a greater frequency? B) A)

(nm) What is the Frequency?? Time = 1 second Hint: Frequency = wavelengths per second Answer: 4 Hz

(nm) What is the Frequency?? Time = 2 seconds Hint: Frequency = wavelengths per second Answer: 2 Hz

(nm) What is the Frequency?? Time = 0.5 seconds Hint: Frequency = wavelengths per second Answer: 8 Hz

Question 1 A rhythmic disturbance that carries energy but not matter is known as a _______. A. electron B. matter C. volcano D. wave

The correct answer is D. Think of the wave that you send across a bed sheet by shaking one end. Matter does not move across the bed sheet, only energy. Answer

The sound of someone clapping their hands is a wave. Can you explain how? Energy from the clap moves out through the air; it is a rhythmic disturbance that travels away from the source. Answer Question 2

Why wouldn’t a drum solo sound good in outer space? You wouldn’t be able to hear a drum in outer space. Where there’s no air, there can be no compression and rarefaction, and thus no sound waves. Answer Question 3

What is represented by letter C in this illustration? A. amplitude B. crest C. rest position D. trough Question 4

The answer is A. The amplitude of a transverse wave is a measure of how high the crests are or how deep the troughs are. Answer

The amplitude of a transverse wave is _______ the distance between a crest and a trough. A. one-eighth B. one-fourth C. one-third D. one-half Question 5

The answer is D. The amplitude of a transverse wave is one-half the distance between a crest and a trough. Answer