Properties of Waves
The Ripple Tank
• To study waves, we will
use a ripple tank. A ripple
tank works by having a
wave generating probe
produce a continuous
wave in the water. The
ripple tank has a glass
bottom that allows light to
be projected down
through the water and the
glass onto a screen
below the table
Rectilinear Propagation
Rectilinear Propagation for Straight Waves
• Straight waves are produced by
periodically dipping a long straight edge
probe into the water.
• For straight waves, the path of two points
show that the direction of propagation of
the advancing straight wave is
perpendicular to the wave front.
Rectilinear Propagation for Circular Waves
• Circular waves are created by periodically
dipping a pointed probe into the water.
• The direction of propagation of the two
segments of the advancing circular wave
lie along radial lines away from the center
of disturbance. (See diagram on
chalkboard).
Reflection
• Some examples of reflection are echoes
from walls, reflection of light off a mirror,
and the reflection of water waves from the
edge of a pool.
When does reflection occur?
• A wave is turned back, or reflected, when
it encounters a barrier that is the boundary
of the medium in which the wave is
traveling.
Reflection of Straight Waves
• Case 1: The wave fronts are parallel to the
boundary.
• In this case, both the direction of
propagation of the incident waves and the
reflected waves will lie perpendicular to
the surface of the barrier. See diagram on
board.
Straight Waves continued
• Case 2: The barrier is
turned at an angle to
the incident waves
The Law of Reflection
• The Law of Reflection states that when a
wave disturbance is reflected at the
boundary of a transmitting medium, the
angle of incidence (Θi) will equal the angle
of reflection (Θr).
Partial and Complete Reflection
• Reflection may be partial or complete
depending on the nature of the reflecting
boundary. If there is no boundary
mechanism for extracting energy from the
wave, all of the energy incident with the
wave is reflected back.
Free end termination
• A wave crest is reflected back as a wave
crest and a trough as a trough during free
end termination reflection. This occurs
when the reflecting medium is less dense
than the medium in which the waves are
traveling.
Free end termination diagram
Longitudinal Waves
• Longitudinal waves reflect from a less
dense material with a change in phase.
That is, if sound traveling in a solid reflects
from air back into the solid, a compression
will reflect as a rarefaction and a
rarefaction as a compression.
Fixed end termination reflection
• Reflection from a fixed end occurs with a
180 degree phase shift. That is, a crest
will reflect back as a trough and a trough
as a crest. This occurs when the reflecting
medium is more dense than the medium in
which the wave is traveling.
Fixed end reflection diagram
Longitudinal Waves
• Longitudinal waves reflect from a more
dense material without a change in phase.
That is, if sound traveling in air reflects
from a solid back into the air, a
compression will reflect as a compression
and a rarefaction as a rarefaction.
Refraction
• The properties of the medium through
which a certain wave disturbance travels
determines the propagation speed of that
disturbance.
• Traveling waves passing from one medium
into another experience a change of speed
at the interface (boundary) of the two
materials.
Waves traveling from deep to
shallow water
Waves traveling from deep to
shallow water at an angle
Diffraction
• Diffraction is the spreading of a wave
disturbance beyond the edge of a barrier.
Fixed Aperture
• When waves of different wavelengths
encounter a fixed aperture (opening) size,
the extent to which diffraction occurs
varies. See diagram on board.
• Conclusion: For a fixed aperture, as
wavelength increases, diffraction also
increases.
Fixed Wavelength
• When waves of a fixed wavelength
encounter different aperture sizes, the
extent to which the waves diffract varies.
See diagram on board.
• Conclusion: For waves of a fixed
wavelength, as aperture size increases,
diffraction decreases.
Superposition Principle
• When two or more waves travel
simultaneously through the same medium,
(1) Each wave proceeds independently as
though no other waves were present and
(2) the resultant displacement of any
particle at a given time is the vector sum of
the displacement that the individual waves
acting alone would give.
Interference
• The term interference is used to describe
the effects produced by two or more
waves that superpose while passing
through a given region.
Constructive Interference
• When two waves are added together and
the resulting displacement for a given
particle is greater than it had been in either
of the waves being added, the waves are
said to interfere constructively.
Constructive Interference
Destructive Interference
• When two waves are added together and
the resulting displacement for a given
particle is less than it had been in either of
the waves being added, the waves are
said to interfere destructively.
Destructive Interference