Section 15-2: Characteristics of Waves
A. Wave Properties
1. sine curve – curve on graph which looks like an S lying on its side
a. used to represent transverse waves and to describe their properties
b. sine wave – wave that has the shape of a sine curve
2. amplitude – maximum distance that the particles of a wave’s medium vibrate from their rest
position; half the vertical distance between the trough and the crest; expressed in
meters; Fig. 1, p. 514, bottom left
a. crest – highest point of a wave
b. trough – lowest point of a wave
3. longitudinal waves also have characteristic parts
a. compression – point of highest density in a longitudinal wave; corresponds to crest
b. rarefaction – portion of wave in which the density and pressure of the medium are at
a minimum; stretched out areas of a longitudinal wave; corresponds to trough
c. amplitude – maximum deviation from the normal density or pressure of the medium;
a large amplitude indicates large energy
4. wavelength – distance from any point on a wave to an identical point on the next wave;
Fig. 2, p. 515, top
a. transverse wave: crest to crest or trough to trough
b. longitudinal wave: between two compressions or two rarefactions
c. if source of a wave vibrates in an irregular way, wavelength may change over time
d. represented by Greek letter lambda, ; expressed in SI unit, meters (m)
5. period – time that it takes a complete cycle or wave oscillation to occur
a. time between two successive crests
b. represented by symbol, T, expressed in SI unit, seconds (s)
15-2b
6. frequency – number of cycles or vibrations per unit of time; Fig. 4, p. 516, bottom left
a. number of full waves to pass a point in a given period of time
b. symbol is f, and the SI unit is the hertz, (Hz); 1/s
c. frequency-period equation –
inverse relationship
frequency = 1/period
f=1/T
B. Wave Speed
1. wave speed equals frequency times wavelength or wavelength divided by period
a. speed of moving object is determined by dividing the distance traveled by the time
speed = distance/time v = d / t
SI units, m/s
b. determining the speed of a wave: speed = wavelength/period
v=/T
c. period is the inverse of the frequency; dividing by the period is equivalent to
multiplying by the frequency
d. wave speed equation –
wave speed = frequencywavelength
v = f
2. speed of wave depends on the medium
3. kinetic theory explains differences in wave speed
4. light has finite speed: 3.00108 m/s in empty space; represented by symbol, c; light
moves more slowly in air or in water
Math Skills p. 519, bottom
15-2c
C. The Doppler Effect
1. an example; ambulance passes and sound of siren changes from high pitch to lower pitch
2. pitch – measure of how high or low a sound is perceived to be depending on the frequency
of the sound wave; higher-pitched sound is caused by sound waves of higher frequency
3. frequency changes when the source of waves is moving
3. Doppler effect – an observed change in the frequency of a wave when the source or observer
is moving
a. ambulance moving toward you; sound reaches the ear at higher frequency and higher
pitch
b. ambulance moving away from you; sound waves reach the ear at a lower frequency
and a lower pitch
c. Doppler effect occurs for many types of waves, including sound waves and light
waves