Mav Mark
9/16/11
s = 50 cm/s
λ = 10 cm
f=?
Characteristics of
Waves
Part II
Reflection
• When an object or a wave hits a
surface through which it cannot pass, it
bounces back.
• Reflection is the bouncing back of a
wave or object from a surface.
• For example, if you throw a ball at a
wall, the ball bounces back. The ball is
reflected by the wall.
Reflection
• Sound waves bounce off walls and
other hard surfaces. Reflected sound
waves are called echoes.
• Light waves bounce off mirrors and
other shiny surfaces. You see your face
in a mirror because light from your face
bounces from the mirror to your eyes.
Reflection
• Law of Reflection - The angle of
incidence is always equal to the angle
of reflection.
Refraction
• When a wave enters a new medium at
an angle, one side of a wave changes
speed before the other side, causing
the wave to bend.
• Refraction is the bending of a wave
due to a change in speed. Refraction
happens only when a wave enters a
new medium at an angle.
Refraction
• Light travels slower through water than
through air. So, when light enters water,
it slows down.
• If a light wave passes from air into
water - at an angle - one side of the
light wave enters the water before the
other side. This causes the light to
bend.
Diffraction
• When a wave moves around a barrier
or through an opening in a barrier, it
bends and spreads out.
• Diffraction is the bending and
spreading out of waves. Diffraction
happens when waves go around a
barrier or through a hole in a barrier.
Interference
• There are two types of interference:
constructive and destructive
• Interference is what happens between
waves that bump into one another.
When waves interfere, the waves
combine to form a single wave.
Interference
•
•
Constructive interference happens when
the crests of one wave pass through the
crests of another wave. The two waves
combine to make a wave with a larger
amplitude.
Destructive interference happens when
the crests of one wave pass through the low
points of another wave. The two waves
combine to make a wave with a smaller
amplitude.
Types of Seismic
Waves
• Seismic waves include P waves, S
waves, and surface waves.
• Earthquakes cause waves that move
through the ground. Earthquake waves
are called seismic waves.
Types of Seismic Waves
•
•
•
P (primary) waves are longitudinal waves. P
waves move more quickly than other types of
seismic waves.
S (secondary) waves are transverse waves. S
waves cannot travel through liquids, including
Earth’s liquid outer core. Because of this, if you are
on the other side of the planet, you can primarily
only feel P waves.
Surface waves are a combination of of
longitudinal and transverse waves. Surface waves
move more slowly then P waves or S waves. They
also cause more damage than P waves or S
waves.
Globe video
Types of Seismic
Waves
• Tsunamis are huge surface waves in
oceans. They are caused by
underwater earthquakes.
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•
•
Detecting Seismic
Waves
A seismograph records the ground movements
caused by seismic waves are they move
through Earth.
Seismographs are instruments that measure
earthquake waves.
Seismographs can be used to find where an
earthquake happened by measuring the time
between a P wave and an S wave.
Seismographs can also be used to find
underground resources, such as oil and water.