CHARACTERISTICS OF WAVES

Chapter 15, Section 2, pp 514-523

A. __________

• Represents the amount of __________ carried by the wave

AMPLITUDE

•The maximum movement of a wave from ________.

• Measured from rest to ________ (top of the wave) or rest to __________ (bottom).

REST

CRESTTROUGH

ENERGY

Ex: A sound wave with more energy and greater amplitude is __________LOUDER!

Earth Harp

AM

PL

ITU

DE

• The intensity of an earthquake is determined by the _____________ of the original disturbance and waves.

AMPLITUDE

• Earthquake energy measured by a

_________________.SEISMOMETER

• The distance between two equivalent parts of a wave. Ex: from ________ to ________

CREST

B. ______________WAVELENGTH

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.

• Ex: Time between crests in a wave pool

WAVELENGTH

D. ________________FREQUENCY• The number of complete waves per unit of time (waves/second)

• Unit = _________.

• Distinguishes one color of ______ from another, or whether or not a _______ is audible.

Hertz (Hz)

SOUND LIGHT

• 1 Hz = 1 vibration / sec

Frequency = 1

T (period)

Frequency vs. PeriodFrequency 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.

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…

the frequencies…

• Ex: Humans hear from 20-20,000 Hz

• Mosquito ring tones

SAME

Different sounds…• In the same medium, sound travels at the

______ speed. What makes differently pitched (high/low) sounds? _______________

• 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

1500 m/s 340 m/s3,800 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)

distancetime

So… wave speed = wavelength ÷ period

• 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 = λ T

v = f x λ

V

λ

T

f

V

λ

Practice ProblemThe 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

Equation =

Solution:

v = 262 Hz x 1.30 m

v = 341 m/s

v = f x λ

Variables: v= ? f= 262 Hz λ= 1.30m

The Doppler Effect• An observed change in the ____________ of a wave when the source of the wave or the observer is _________MOVING

FREQUENCY

Train Horn Doppler

Fire Engine Siren Doppler

BLUESHIFT

REDSHIFT

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. The speed of light is _________ m/s. Calculate the frequency of green light waves with this wavelength.

0.523,000

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)?

340220

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

0.0085 3,000