Waves
• The medium is the material
through which a wave moves
Type of Wave Medium
Ocean water
Sound air molecules
light zero
electromagnetic zip
Crests and Troughs
• Crests are the highest points of a
wave;
• Troughs are the lowest points of a
wave.
Amplitude
• The maximum displacement of the wave.
• Distance from mid-point to crest or trough.
• Indicates the intensity, energy or power in
a wave
Wavelength
• Distance from crest to crest or
trough to trough.
Frequency (f)
• Frequency is the number of
waves past a point/second.
• The unit is the Hertz. (Hz)
• 1 Hz = 1/sec.
Speed is frequency * wavelength
v=f
In 1st semester: v = d/t
note: =d
f = 1/t
so: v = f = d/t
If train cars are 18 m long and 3
For example:
cars pass each second, how fast is the
train going?
v = f
List
v = 18(3)
= 18 m
v = 54 m/s
f = 3 Hz
In km/hr:
v=? 54 m 3600 s 1 km = 194.4 km/hr.
s 1 hr. 1000m 121.5
mi/hr.
Period (T)
• The amount of time (in sec.) it
takes for a particle to complete
a wave motion.
• reciprocal of frequency.
• T = 1/f
• f = 1/T
What is the frequency if the period is 5s?
List
f=? f = 1/T
T=5s f = 1/5 s = 0.2 Hz
Problems: text p 388 #’s 21-25, 36-38
Pulse
As a wave moves through a
medium it has a pulse.
Waves transmit energy
• Waves transmit energy from
one place to another.
• The medium ends up where
it started.
Wave Types
• Transverse – up & down motion
–Surface
–Electromagnetic
–String
• Longitudinal – back & forth motion
–Sound
Transverse Waves
• In transverse wave, the
particles of the medium
move in a direction
perpendicular to the
direction of the wave.
Longitudinal Wave
• In a longitudinal wave, the
particles of the medium move in a
direction parallel to the direction
of the wave.
• Sound is an example of a
longitudinal wave.
• In longitudinal waves, the
medium compresses and
releases.
A vibrating Tuning Fork will
Surface Waves
• In surface waves, the medium
undergoes a circular motion.
Electromagnetic Waves
• Electromagnetic Waves do not
require a medium
• Electromagnetic waves are the
only waves that can travel
through space. (A vacuum)
• More on this later.
Mechanical Waves
A mechanical wave is a
disturbance created by a vibrating
object. The energy from the
disturbance is transmitted from
one area to another across the
medium.
Mechanical Waves
• Mechanical Waves are not
capable of being transmitted
through a vacuum.
• Which of the previous waves
are mechanical waves?
Problems
• p 389
– #’s 39,40
• p 683
– #’s 1-8 (Vibrations and Waves)
Imagine:
• You toss a pebble into a pond.
• It creates ripples that travel
outward as concentric circles until
they reach the edges of the pond.
• What they do then, we will
discuss later.
Ocean Waves
• Demonstrate characteristics of
wave motion.
• Ocean waves form in many ways.
Ocean Wave Types
• Some types of Ocean Waves are:
–Wind Generated
–Tides
–Tsunamis
Traveling Wave / Standing Wave
• Traveling waves move across a
medium. (ripples on the pond)
• A standing wave appears to not be
moving, but that is just an illusion.
Standing Waves result from..
• Interference.
• Interference occurs when two or more
waves encounter each other in such a
way that crests and/or troughs
interact.
• If one crest is at the same location as
the crest of a second wave, the two
crests add together.
• If a crest of one wave encounters a trough
of a second wave, the crest and trough
subtract from one another. If they were
equal in size, there is no longer a trough
or a crest.
Constructive Interference
Constructive Interference
Destructive Interference
• Since these waves are equal and
opposite, they obliterate one another.
If two waves are equal in size
and have the right frequency…
• A standing wave forms in which
the crests and troughs seem to not
move.
• Point A vibrates back and forth
vertically, but always returns to
the same spot. Antinode
• Point B does not move and is
called a stationary node.
Other Wave Topics
• Doppler Effect sound
• Reflection
• Refraction light
• Diffraction