Download What is a Wave?

WAVES:
Types and Properties
What is a Wave?
• A wave is a
repeating
disturbance or
movement that
transfers
energy through
matter or space
The Nature of Waves
• Waves transfer energy not matter. Waves
can only exist as long as they have energy to
carry.
How is Energy Carried?
• Molecules of matter bump each other and
pass energy from molecule to molecule.
What are Mechanical Waves?
• Mechanical
waves are waves
which require a
medium.
•A medium is a form of matter through
which the wave travels (such as water,
air, glass, etc.)
Two Shapes 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
Example: Seismic Waves
• Like water waves, seismic
waves are mechanical,
transverse waves
• A seismic wave is an energy
wave which vibrates through
the earth’s crust as the crust
bends or breaks.
• Some travel through the
earth and some travel
across the earth’s surface.
Anatomy of a Seismic Wave
Compressional Waves
• In a compressional wave the matter in the
wave moves back and forth, parallel to the
direction of the wave
• Example: sound 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
What are Electromagnetic Waves?
• 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
– UV waves
microwaves
– X rays
infrared waves – gamma rays
visible light waves
Wave Properties: Transverse
• Crest: top of
the wave
• Trough:
bottom of the
wave
• Rest
Position: half
way between
the crest and
trough
Waves
Wave Properties: Transverse Waves
• 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: Amplitude
• The lower the amplitude, the less energy the wave
carries.
• The greater the amplitude, the more energy the
wave carries.
A)
B)
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)
Wave Properties: Compressional Waves
• The amplitude of a compressional wave is
determined by the closeness of the compressions.
•The closer the compression lines and the farther
the rarefaction lines, the greater the amplitude, the
greater the energy.
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
Color and Pitch
• COLOR: the
wavelength &
frequency of a light
wave determines the
color of the light.
• PITCH: the wavelength &
frequency of a sound wave
determines the pitch of a
sound.
What is the Wavelength??
5 10 15 20 25 30 35 40
(nm)
Wavelength = 25 nm – 5 nm = 20 nm
What is the Wavelength??
5
10
15
20
25
(nm)
Wavelength = 15 nm – 10 nm = 5 nm
Which has a greater Amplitude?
A)
B)
Which has more energy?
A)
B)
Which has a greater wavelength?
A)
B)
Which has a greater frequency?
A)
B)
What is the Frequency??
5 10 15 20 25 30 35 40
(nm)
• Time = 1 second
• Hint: Frequency = wavelengths per second
• Answer: 4 Hz
What is the Frequency??
5 10 15 20 25 30 35 40
(nm)
• Time = 2 seconds
• Hint: Frequency = wavelengths per second
• Answer: 2 Hz
What is the Frequency??
5 10 15 20 25 30 35 40
(nm)
• Time = 0.5 seconds
• Hint: Frequency = wavelengths per second
• Answer: 8 Hz
Wave Speed
• The speed at which a wave travels is its
wave speed.
• wave speed (v) = wavelength () *
frequency (f)
• Wavelength is represented by the Greek letter lambda (λ) and
frequency is represented by (f)
• Sound travels through air at about 340 m/s. Light travels
through air at about 300,000,000 m/s.
What is the Wave Speed??
wave speed = wavelength * frequency
5 10 15 20 25 30 35 40
(m)
Time = 1 second
Frequency = 4 hz
Wavelength = 25 m – 5 m = 20 m
Wave Speed = 20m * 4hz = 80 m/s
What is the Wave Speed??
wave speed = wavelength * frequency
5
10
15
20
25
(m)
Time = 1 second
Frequency = 9 hz
Wavelength = 15 m – 10 m = 5 m
Wave Speed = 5m * 9hz = 45 m/s
Question 1
A rhythmic disturbance that carries energy
but not matter is known as a _______.
A. electron
B. matter
C. volcano
D. wave
Question 2
The sound of someone clapping their hands
is a wave. What kind and shape is it?
Question 3
Why wouldn’t a drum solo sound good in
outer space?
Question 4
What shapes of waves are depicted below?
A
B
Question 5
Label each of the following 4 letters:
A. ____________
B. ____________
C. ____________
D. ____________
Question 6
On this compressional wave, what do
letters A and B represent?
A
B
Question 7
The amplitude of a wave is also a measure
of the wave’s __________.
A. compression
B. wavelength
C. energy
D. motion
Question 8
5 10 15 20 25 30 35 40
(nm)
What is the frequency of this transverse wave
if time = 2 seconds
• Hint: Frequency = wavelengths per second
Question 9
If a wave has a frequency of 500 Hz and a
wavelength of 90 m, what is its speed?
wave speed (v) = wavelength () * frequency (f)
Question 10
wave speed = wavelength * frequency
5
10
15
20
25
(m)
A) Determine the frequency and wavelength
if time is 0.5 seconds
B) Calculate the wave speed
Answer 1
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 2
Energy from the clap moves out through the
air. It is a mechanical wave because it needs
a medium. It is also a compressional wave
because of its shape.
Answer 3
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 4
A
B
A) Compressional
B) Transverse
Answer 5
A. Crest
B. Trough
C. Amplitude
D. Rest Position
Answer 6
A) Rarefaction
B) Compression
A
B
Answer 7
5 10 15 20 25 30 35 40
(nm)
There are 4 wavelengths in 2 seconds which
means there are 2 wavelengths in 1 second.
Thus the frequency is 2 Hz.
Answer 8
The answer is C, energy. The greater a
wave’s amplitude, the more energy it
carries and vice versa.
Answer 9
The wave speed is 500Hz * 90m = 45,000 m/s.
Wave speed is calculated by multiplying
frequency times the wavelength.
Answer 10
wave speed = wavelength * frequency
5
10
15
20
25
(m)
Time = 0.5 seconds
Frequency = 9*2 = 18 hz
Wavelength = 15 m – 10 m = 5 m
Wave Speed = 5m * 18hz = 90 m/s