Physics STP Waves Study Guide
Wave: A regular, repeating disturbance that carries energy.
Properties of Waves: Amplitude, Frequency, Period, Wavelength
Property / Units / DefinitionAmplitude / m / Distance from median to peak. Energy of the wave.
Frequency / Hz / Number of cycles per second.
Period / s / Time for one cycle.
Wavelength / m / Distance from peak to peak.
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. How about in a vacuum?
Slowest / 2 / 3 / FastestDiffraction: The bending of a wave around an obstacle or through an opening.
The alternating light and dark pattern occurs Plane waves that encounter a small opening create
due to constructive and destructive interference. 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 When passing into a material with greater density,
different angles. This is why a prism separates waves will bend toward the vector that is normal to
white light into its constituent colors. 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 / Color Shift of Light / Change in Pitch of Sound / Change in FrequencyTowards Each Other
Away From Each Other
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?