Physics STP Waves Study Guide
Wave: A regular, repeating disturbance that carries energy.
Properties of Waves: Amplitude, Frequency, Period, Wavelength
Property
Amplitude
Frequency
Period
Units
Definition
m
s
Distance from median to
peak. Energy of the wave.
Number of cycles per
second.
Time for one cycle.
Wavelength
m
Distance from peak to peak.
Hz
Interference: When waves collide!
No two objects can occupy the same space at the same time, but waves can.
These waves are in-phase, meaning that
their crests match up with each other. This
produces constructive interference, and the
waves add together.
These waves are out-of-phase, meaning that
the crests of one wave match up with the
troughs of the other. This produces
destructive interference, and the waves
cancel each other out.
Transverse and Longitudinal Waves
* Longitudinal waves move in the direction of the disturbance.
* Sound waves are longitudinal.
* Transverse waves move perpendicular to the
direction of the disturbance.
* Light waves are transverse.
Wave Anatomy
Label the following on the image: Crest, trough, median, wavelength, and amplitude.
Sound
* Sound requires a medium – sound can not travel through a vacuum.
* The speed of sound increases in substances with higher density.
Rank the following in order of increasing speed of sound: In water, in iron, in air, in wood.
Slowest
2
3
How about in a vacuum?
Fastest
Diffraction: The bending of a wave around an obstacle or through an opening.
The alternating light and dark pattern occurs
due to constructive and destructive interference.
Plane waves that encounter a small opening create
new waves that looks like they came from a point source.
Refraction: The Bending of a Wave as it Crosses a Boundary at an Angle
Cause: The speed of light changes when passing through materials of different densities. This causes the light waves to
bend! The speed of light in a vacuum is 3 x 108 m/s. Light slows down when passing through objects.
Light of different wavelengths are bent at slightly
different angles. This is why a prism separates
white light into its constituent colors.
When passing into a material with greater density,
waves will bend toward the vector that is normal to
the surface of the material.
Reflection: When a wave reaches a boundary, some or all of the wave bounces off.
Reflected waves always come off the surface at the same
angle.
Law of Reflection:
Angle of Incidence = Angle of Reflection
The Doppler Effect: The apparent change in the frequency of waves due to the
movement of the source or observer.
Source and
Observer Motion
Towards Each
Other
Away From Each
Other
Color Shift of Light
Change in Pitch of Sound
Change in Frequency
Polarization: All waves are vibrating in the same direction.
When light passes through a polarizer, all the light is filtered
out except that which is vibrating in one direction.
If light passes through a vertical polarizer and then through a
horizontal polarizer, all the light will be filtered out, so no
light will pass through both.
Key facts:
* Light travels at 3 x 108 m/s.
* Light is one type of electromagnetic wave. Radio waves, infrared waves, and cosmic rays are other types. The only
difference between these types of waves are the frequency and wavelength (and therefore the energies).
* Light is made up of particles called photons. Sometime these particles act like waves. (Quantum mechanics is very
strange!)
Highlight and Identify the Key Quantities in Each Exercise – then Solve
1) Ripples on a pond go up and down once every .15 seconds. What is the frequency?
2) The wings of a crow flap once every 0.5 seconds. The flapping creates sound waves that travel at 320 m/s. What is
the wavelength of the sound waves?
3) A piece of wood floats in the ocean, bobbing once every 1.2 seconds. If the distance between the waves is 1.5
meters, what is the speed of the ocean waves?
4) In a tube, the distance between the mouthpiece and the bell is 0.8 meters. It produces waves of sound that travel at
360 m/s. What is the frequency of the sound waves?