Waves
What do you
know?
Types of waves
• Mechanical – need a medium or material
to travel through ex. Water, slinky
• Electromagnetic- do not need materials to
travel ex. Xrays, light
• Waves transmit energy through space or
materials
Transverse Waves
• The wave travels
perpendicular to
the motion of the
matter being
displaced
Anatomy of a wave
• Six properties of
waves
• Frequency
• Wavelength
• Velocity
• Amplitude
• period
AMPLITUDE
• Distance between the normal and the top
or bottom of a wave.
• The greater the amplitude, the greater the
energy of the wave or the greater the
energy went in to producing a wave.
• Ripple vs tsunami
Frequency
• The number of times a wave passes a
point in a given time period.
• Measure in hertz.
• 1 hz = a cycle per second
Wavelength
• The distance between 2 crests or troughs.
• Long wavelengths usually mean low
frequencies
Period
• Time it takes for a cycle or disturbance to
occur
• Time from crest to crest or trough to
trough
• Period and frequency are determined by
the source of that wave. They do not
depend on the wave’s speed or the
medium.
Velocity
• The speed of a wave formula
• Velocity = wavelength X frequency
• Velocity is determined by the material that
the wave is traveling through.
• EX. Sound travels in water at a different
speed than in air.
• Temp and viscosity can effect velocity.
Speed
• Sound travels at 343 m/s in air.
Ex. problems
• A sound wave has a frequency of 262 Hz
and a wavelength of 1.29m. What is the
speed of the wave?
Longitudinal wave
• Particles
•
•
vibrate
parallel to the
motion of a
wave as in
earthquakes
and sound.
Compressions
rarefactions
Longitudinal waves
• Waves transmitted in fluids and air are
longitudinal
• This includes sound and water waves
• Water waves at the surface of water have
both longitudinal and transverse
characteristics. These are known as
surface waves.
One of three things happens to
waves when they hit a barrier or
change mediums.
• Reflection
• Refraction
• Diffraction
Reflection
• All or part of a wave
•
bounces back or
returns
The approaching
wave is the incident
wave
What happens when a wave hits a
more rigid barrier.
• The reflected waves comes back inverted
or upside down.
What happens when a wave enters
a less rigid medium?
• The reflected wave returns right side up or
erect.
Law of Reflection
• Normal is
perpendicular to
surface of a
barrier
Refraction
• Waves are bent when
•
•
they hit a barrier or
change media
Ex. Water wave on
the shore
Light traveling
through glass (
broken pencil trick)
Diffraction
• When a wave bends
around a barrier.
Diffraction of water waves
• http://www.smeter.net/propagation/diffra
c1.php
Interference
• When 2 waves
•
•
traveling in opposing
directions cross one
another interference
occurs.
These may cancel one
another out.
Can you see where
interference occurs.
Constructive interference
Destructive interference
•
•
Polarization of a wave occurs
when light is restricted to one
plane.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the polarizer
is rotated to transmit the reflections as well as possible; by rotating the polarizer by 90°
(picture on the right) almost all specularly reflected sunlight is blocked.
Polarizing film
•
Sound Waves
• Longitudinal
• Their amplitude is measured in decibels.
This is a measure of their loudness.
Their frequency is heard as its pitch.
Speed in air is 343 m/s.
Resonance
• Resonance is usually
•
associated with sound
waves.
This occurs when the
vibrations of one
object are picked up
by another and it
vibrates in sync.
Pitch
• Pitch in sound waves refers to the
frequency of the sound wave.
• Amplitude of a sound wave is measured in
dedibels and refers to the strength or
energy of the waves.