CHARACTERISTICS OF WAVES Chapter 15, Section 2, pp 514-523

A. __________ AMPLITUDE REST CREST TROUGH ENERGY Earth Harp The maximum movement of a wave from ________. REST CREST Measured from rest to ________ (top of the wave) or rest to __________ (bottom). TROUGH ENERGY Represents the amount of __________ carried by the wave Ex: A sound wave with more energy and greater amplitude is __________ LOUDER!

AMPLITUDE

The intensity of an earthquake is determined by the _____________ of the original disturbance and waves. AMPLITUDE Earthquake energy measured by a _________________. SEISMOMETER

WAVELENGTH B. ______________  The distance between two equivalent parts of a wave. Ex: from ________ to ________ CREST CREST  Symbol = ___ (Greek letter _______) Lambda unit = ______ meter

shorter wavelengths carry _______ energy than longer wavelengths. MORE

C. _______ PERIOD the time (seconds) required for one full _____________ of a wave to pass a certain point. WAVELENGTH Ex: Time between crests in a wave pool

FREQUENCY D. ________________ The number of complete waves per unit of time (waves/second) Unit = _________. Hertz (Hz) 1 Hz = 1 vibration / sec Distinguishes one color of ______ from another, or whether or not a _______ is audible. LIGHT SOUND Frequency = 1 T (period)

Frequency vs. Period Frequency Period How often something happens Time it takes something to happen (start to finish) Rate quantity Time quantity Cycles/second Seconds/cycle Example: If the woodpecker drums upon a tree 2 times in one second, then the frequency is 2 Hz. Each drum must endure for one-half a second, so the period is 0.5 s.

Floating along……… Suppose you are floating on an inner tube in the ocean. A wave crest passes the inner tube every 2 seconds. Period: 2s (total time for one complete wave/oscillation to occur) Frequency: f = _1_ f = 1 T 2 f = 0.5 Hz

Different colors… In the same medium, light travels at the _____ speed (300,000,000 m/s or 186,000 mph). What makes the colors different? ___________ SAME frequencies…

Different sounds… In the same medium, sound travels at the ______ speed. What makes differently pitched (high/low) sounds? _______________ SAME the frequencies… Ex: Humans hear from 20-20,000 Hz Mosquito ring tones

For two waves moving at the SAME speed, as  INCREASES, frequency ____________ DECREASES In addition, as the period of a wave decreases, the frequency _____________ (INVERSE relationship) INCREASES

Wave Speed The speed of a wave depends on the ________. MEDIUM In a given medium, the speed of a wave is ____________. CONSTANT 3,800 m/s 1500 m/s 340 m/s WHY DOES SPEED DIFFER?

The speed of a wave is equal to wavelength divided by period, or to frequency multiplied by wavelength. Remember… the speed of a moving object is found by dividing the ________ the object travels by the ____ it takes the object to travel that distance or… speed = distance / time (v = d / t) distance time

So… wave speed = wavelength ÷ period λ V T Because wave speed is the inverse of frequency, dividing by the period is equivalent to multiplying by the frequency. Therefore the speed of a wave can also be calculated: wave speed = frequency × wavelength v = f x λ V f λ

Practice Problem The string of a piano that produces the note middle C vibrates with a frequency of ____ Hz. If the sound waves produced by this string have a wavelength in air of ____ m, what is the speed of the sound waves? Given: Unknown: frequency, f = 262 Hz wave speed, v = ? m/s wavelength, λ = 1.30 m 262 1.30

v = f x λ Variables: v= ? f= 262 Hz λ= 1.30m Equation = Solution: v = 262 Hz x 1.30 m v = 341 m/s

The Doppler Effect An observed change in the ____________ of a wave when the source of the wave or the observer is _________ FREQUENCY MOVING

Fire Engine Siren Doppler Train Horn Doppler Fire Engine Siren Doppler

REDSHIFT BLUESHIFT

Doppler Big Bang

More wave speed practice problems 1. The average wavelength in a series of ocean waves is _____ m. A wave crest arrives at the shore on average every ____ s, so the frequency is ______ Hz. What is the average speed of the wave? 15.0 10.0 0.100

2. Green light has a wavelength of __________ m 2. Green light has a wavelength of __________ m. The speed of light is _________ m/s. Calculate the frequency of green light waves with this wavelength. 0.52 3,000

3. The speed of sound in air is about _____ m/s 3. The speed of sound in air is about _____ m/s. What is the wavelength of a sound wave with a frequency of _____ Hz (on a piano, the A below middle C)? 340 220

4. Calculate the frequency of microwaves that have a wavelength of _______ m and a speed of _________ m/s. 0.0085 3,000