Waves
A wave is a rhythmic disturbance that carries energy
through matter or space.
Water waves, sound waves, and the waves that travel
down a rope or spring are types of mechanical waves.
Mechanical waves require a medium.
A wave pulse is a single bump or disturbance that
travels through a medium. If the disturbance is
continuous, a continuous wave is generated.
It is important to distinguish between the motion of the wave and the
motion of the individual particles in the wave. In general, waves travel
from place to place, but the particles in a wave oscillate back and forth
about one location.
For example, a "wave" at a ballgame travels around the stadium, but the
individual people making up the wave simply stand up and sit down.
Waves transmit ENERGY but not MATTER.
Transverse Waves
• The medium (the material the energy/wave travels in) and the
energy travel perpendicular to each other.
• The crest/troughs are the high/low points along the medium.
• The amplitude refers to the energy that the wave has. Larger
amplitude= more energy.
• The wavelength can be determined by measuring the distance
from ANY point on the wave, and the next point just like it. For
example, crest to crest or trough to trough.
wavelength
Compressional/Longitudinal Wave
• The medium and the energy travel parallel to each other. The medium travels back
and forth and really goes no where ultimately. But the energy does travel horizontally
as well and does go somewhere.
• The dense regions are referred to as compressions and the less dense regions,
expansions, are more often referred to as rarefactions.
• The wavelength can be measured in the same way, from any point to the next point
just like it. For example, from the start of one compression to the start of the next
compression.
• Amplitude in a compressional wave can be determined by how dense the
compressions are. The more dense the more energy or amplitude.
Examples of Compressional and
Transverse Waves
Sound
Wave on a Rope
Example of Combination Waves
Surface Waves
& Seismic
(Earthquake)
Waves
Calculating the Velocity of a wave
v=λf
v- velocity (m/s)
λ- wavelength (m)
f- frequency (Hz= 1/s)
v= Δd/ Δt
v- velocity (m/s)
Δd- distance wave travels (m)
Δt- time (s)
Period vs Frequency
The PERIOD is defined as the number of seconds it takes to
complete just one wave cycle. It should be measured in seconds.
If not, convert with a smile on your face.
The FREQUENCY is defined as the numbers of wave cycles that
occur in just one second. The unit would be cycles/s. However,
cycles isn’t technically a unit so the real unit is 1/s which also
happens to be the same thing as Hertz. Hz=1/s
The two words are inverse or opposites of each other. So,
T= 1/f
and
f=1/T
Waves at Boundaries
When a wave hits a boundary, a portion of the energy (wave) will be transmitted to
the new medium and a portion will be reflected. The more dense the boundary,
the more reflection you will get.
Picture “a” shows an erect incident wave headed toward a very dense
boundary. Picture “b” shows the inverted reflected wave….almost 100%
reflection. Remember, the more dense the boundary, the more reflection
you will get.
Wave Hitting a Less Dense Medium
In this case, we have a more dense spring connected to less dense spring. Notice
in picture “b” the reflected wave is still erect.
BIG IDEA: When an incident wave hits a boundary that is more dense than the
medium it is in, it will reflect with opposite amplitude. When an incident wave
hits a boundary that is less dense than the medium it is in, it will reflect with the
same amplitude.
Law of Reflection
The angle of incidence = the angle of reflection.
Superposition of Waves
Suppose a pulse traveling down a spring meets a reflected
pulse coming back. In this case, two waves exist in the same
place in the medium at the same time. Each wave affects the
medium independently. The displacement of a medium
caused by two or more waves is the algebraic sum of the
displacements caused by the individual waves. This is called
the principle of superposition. In other words, two or more
waves can combine to form a new wave. If the waves are in
opposite directions, they can cancel or form a new wave of
less or greater amplitude. The result of the superposition of
two or more waves is called interference.
Destructive Interference
The superposition of waves
with opposite amplitudes
causes destructive
interference.
When the pulses meet and
are in the same location, the
displacement is zero. Point N,
which doesn’t move at all, is
called a node.
Constructive Interference
Constructive interference occurs when
the wave displacements are in the
same direction. The result is a wave
that has an amplitude larger than any
of the individual waves. The figure to
the right shows the constructive
interference of two equal pulses. A
larger pulse appears at point A when
the two waves meet. Point A has the
largest displacement and is called the
antinode.
Calculating the New Amplitude
Assume left wave to
have amplitude of +3
units, and right wave to
have -3 units. What is
the amplitude of new
wave?
Assume left wave to
have amplitude of +3
units, and right wave to
have +3 units. What is
the amplitude of new
wave?
0, 6, 3
Assume left wave to
have amplitude of +5
units, and right wave to
have -2 units. What is
the amplitude of new
wave?
Standing Waves
are created by continuous
interference.
There is a name for these things:
There are calculations for these things:
Refraction
The change in the direction of waves at the boundary
between two different media is known as refraction. It is
caused by the wave changing speeds as it enters a
different medium.
Bends which direction?
If the wave slows down in the new
medium, it will bend toward the
normal. If the wave speeds up in the
new medium, it will bend away from
the normal.
FST = Fast to Slow, Towards Normal
SFA = Slow to Fast, Away From Normal
Diffraction
Polarization….what does that mean?
A light wave that is vibrating in more than one plane is referred to as unpolarized light.
Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized
light. Such light waves are created by electric charges that vibrate in a variety of
directions, thus creating an electromagnetic wave that vibrates in a variety of directions.
This concept of unpolarized light is rather difficult to visualize. In general, it is helpful to
picture unpolarized light as a wave that has an average of half its vibrations in a
horizontal plane and half of its vibrations in a vertical plane.
It is possible to transform unpolarized light into polarized light. Polarized light waves are
light waves in which the vibrations occur in a single plane. The process of transforming
unpolarized light into polarized light is known as polarization. There are a variety of
methods of polarizing light.
For more info, check out http://www.physicsclassroom.com/class/light/Lesson1/Polarization
Comparison between waves
Is there anything that may need to be clarified in this question?