Wave powerpoint.ppt

Characteristics of Waves
What Are Waves?
Properties of Waves
Interactions of Waves
Seismic Waves
Table of Contents

What are Waves?
• Remember back……
• A wave is a disturbance that transmits energy
through matter or space.

One Way to Classify Waves
Mechanical Waves
•Must have a medium
•Can travel at any
speed
• Ex:
Electromagnetic Waves
•Do NOT need a medium
•Travel at the speed of
light
•Ex:

Characteristics of Waves - What Are Waves?
Mechanical Waves and Energy
Waves travel through water, but they
do not carry the water (or the duck)
with them.

Mechanical Waves
Examples Include:
Ocean waves,
medium = water
Sound waves,
medium = air
Seismic Waves
(Earthquake),
medium = earth

Wave Movement
A wave front is the front of a wave that is transferring energy.
In a single system all of the wave fronts have the same
amount of energy, but as the wave front spreads out, so
does the energy.

Transverse Waves
Waves that move the medium at right angles (perpendicular)
to the direction in which the waves travel are called
transverse waves.

Longitudinal Waves
Longitudinal waves move the medium parallel to the direction
in which the waves travel.

Longitudinal Waves
The compressions of a longitudinal wave correspond to the
crest of a transverse wave. The troughs correspond to
rarefactions.

Transverse vs. Longitudinal Waves
Click on the link to see how the differ waves
travel or propogate.
Another link with animation

Characteristics of Waves - Properties of Waves
Wave Properties
The basic properties of all waves are amplitude, wavelength,
frequency and speed.

Parts of a Wave
Wavelength (λ) is the total
length of 1 wave.
In transverse waves it’s typically
measured from crest to crest or
trough to trough.
In longitudinal waves it’s
measured from compression to
compression or rarefaction to
rarefaction.
The shorter the wavelength, the
more energy the wave is carrying.

Parts of a Wave
Amplitude can be measured on a transverse wave. It height from the
resting point to the crest or the resting point to the trough.
The larger the amplitude, the more energy the wave is carrying.

Wave Measurements
The frequency (f) of a wave
is the number of
complete waves that
pass a given point per
second.
The SI unit for measuring
frequency is Hertz (Hz).
1 waves occurs every
second= 1 Hz
2 waves occur every
second= 2 Hz

Wave Measurements
• Frequency and wavelength have an INVERSE relationship--as
one increases, the other decreases.
• Example: The higher the frequency the shorter the wavelength
and vice versa.

Wave Measurements
Wave speed (v) is the speed at which a wave passes through a
medium and is measured using the following equation:
wave speed (m/s) = frequency (Hz) x wavelength (m)
v = f x λ

Calculations
The speed of a wave on a rope is 50 cm/s and its wavelength is
10 cm. What is the wave’s frequency?
Read and Understand
What information have you been given?
Speed = 50 cm/s
Wavelength = 10 cm
- Properties of Waves

Calculations
Plan and Solve
What quantity are you trying to calculate?
The frequency of a wave = __ Hz
What formula contains the given quantities and the unknown
quantity?
Frequency = Speed/Wavelength
Perform the calculation.
Frequency = Speed/Wavelength = 50 cm/s/10 cm
Frequency = 5/s = 5 Hz

Calculations
Look Back and Check
Does your answer make sense?
The wave speed is 50 cm per second. Because the distance from
crest to crest is 10 cm, five crests will pass a point every second.

Calculating Frequency
Practice Problem
A wave has a wavelength of 2 mm and a frequency of 3
Hz. At what speed does the wave travel?
(2 mm)(3 Hz) = 6 mm/s

Calculating Frequency
Practice Problem
The speed of a wave on a guitar string is 142 m/s and
the frequency is 110 Hz. What is the wavelength of the
wave?
(142 m/s)/(110 Hz) = 1.3 m

STOP HERE 
Lets do the Wave!

Wave Measurements
A wave along a guitar string has a frequency of
440 Hz and a wavelength of 1.5 m. What is the
speed of the wave?
v =
? m/s
f =
440 Hz
λ =
1.5 m
v = 440 Hz x 1.5 m
v = 660 m/s
v = f * λ
v
f * λ

Wave Measurements
The speed of sound in air is about 340 m/s. What
is the wavelength of sound waves produced by
guitar strings vibrating at a frequency of 440 Hz?
v =
340 m/s
f =
440 Hz
λ =
? m
λ = 340 m/s / 440 Hz
λ = 0.77 m
λ = v / f
v
f * λ

Wave Measurements
The speed of light is 3 x 108 m/s. What is the
frequency of microwaves with a wavelength of
0.01 m?
v =
3 x 108 m/s
300,000,000 m/s
f =
? Hz
λ =
0.01 m
f = 300,000,000 m/s / 0.01 m
f = 30,000,000,000 Hz
f = v / λ
v
f * λ

End of Section:
Properties of
Waves

When an object or wave hits a surface through which it
cannot pass, it bounces back.
- Interactions of Waves
Reflection

Reflection
Reflection is when waves, whether physical or
electromagnetic, bounce from a surface back toward the
source. A mirror reflects the image of the observer.
NORMAL

Characteristics of Waves - Interactions of Waves
Refraction
When a wave enters a new medium at an angle, one side of
the wave changes speed before the other side, causing the
wave to bend.

Refraction
Refraction is when waves, whether physical or electromagnetic, are
deflected when the waves go through a substance. The wave
generally changes the angle of its general direction.

Refraction

Diffraction
When a wave moves around a barrier or through an opening
in a barrier, it bends and spreads out.

Diffraction
Diffraction is when a wave goes through a small hole and has a flared
out geometric shadow of the slit.
• a characteristic of waves of all types
• We can hear around a corner because of the diffraction of sound
waves. For instance, if a wall is next to you when you yell, the sound
will parallel the wall. The wall may stop, but the voice doesn't; sound
will almost turn the corner of the wall.

http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/fl
ash/whiteboardcomplete.swf

Wave Behavior
Interference occurs when
the combination of
two or more waves
exist in the same
place at the same
time.
Constructive interference
= bigger wave.
Destructive interference =
smaller wave.

Interference
The interference that occurs when
waves combine to make a wave with
a larger amplitude is called
constructive interference.
The interference that occurs when
waves combine to make a wave with
a smaller amplitude is called
destructive interference.
Link to animation of interference and
standing waves.
Another cool animation!

Wave Interference Activity
Click the Active Art button to open a browser window and
access Active Art about wave interference.

Standing Waves
If the incoming wave and a reflected wave have just the right
frequency, they produce a combined wave that appears to
be standing still.
ex: Jump rope
Link to standing wave animation- watch for >1 min

Standing Waves
Nodes: Point of zero amplitude
Nodes are always spaced evenly throughout the standing
wave.
Antinodes: point of maximum amplitude (MAX energy)

Resonance
• Most objects have a natural frequency of vibration
• If a nearby object vibrates at the same frequency this can
cause resonance.
•Examples: instruments
Show water glass demonstration

Doppler Effect
https://www.youtube.com/watch?v=h4OnBYrbCjY

Question Answer
Asking Questions
Before you read, preview the red headings. In a graphic organizer
like the one below, ask a what, how, when, or where question for
each heading. As you read, write answers to your questions.
How are waves reflected? Waves are reflected when they hit a
surface through which they cannot
pass and bounce back.
What is refraction? The bending of waves due to a
change in speed
When does diffraction occur? When a wave moves around a
barrier or through an opening in a
barrier
What is a standing wave? A wave that appears to stand in one
place even though it is really two
waves interfering

End of Section:
Interactions of
Waves

Graphic Organizer
Longitudinal
Waves
can be
Transverse
can be
contain contain contain contain
Crests Rarefactions
Troughs Compressions

End of Section:
Graphic Organizer

Wave powerpoint.ppt

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