15. Section 2:Waves I. Traveling Waves Traveling wave- a fluctuation traveling in some type of matter, AKA medium. They deliver energy from one location to another. Medium - substance that tends to return to equilibrium when displaced(can be solid, liquid or gas). Amplitude - distance from the peak or trough to equilibrium. When it's positive-peak, when it's negative-trough.
16. Traveling waves(continued) Wavelength - distance for a wave to repeat its motion. Measured from peak to peak or from trough on displacement vs position graph. Period - how long it takes a point at a fixed location on a wave to repeat it's motion. To find it on a displacement vs time graph, measure from peak to peak or trough to trough. Measured in seconds. Frequency - how often a certain wave displacement such as a peak, passes by an observer at a fixed location. It’s the inverse of the period. Unit is Hz or cycles per second Wave velocity -found by multiplying the wavelength and frequency. Represents speed at which the wave is propagating through the medium.
17. Traveling waves(continued) The wavelength depends on the frequency and wave velocity. The frequency depends on the wave source. The wave velocity depends on the medium
18. Transverse Waves For a transverse wave, the displacement of the wave medium is perpendicular (think 90 degrees) to the direction of travel of the wave. Light- a true transverse wave. Transverse vibrations of electric charges create light waves. Frequency of light visible to us is between 4x10^14Hz and 7x10^14Hz. In air, light waves correspond to wavelengths of 700nm(red light) and 400nm(violet light). Human eyes are most sensitive to light with a wavelength of 560nm(yellow-green light).
19. Transverse waves(continued) Light waves- wave that can go through a medium but can also go through a vacuum. The wave speed of light in a vacuum is 3.0x10^8 m/s(c). From a vacuum to any medium, light will slow down. The index of refraction, n, relates how much slower something travels in a given medium compared to how it moves in a vacuum. Equation--> n=c/v . the index of refraction (in a medium) is a unitless ration and has to be greater than one
20. Longitudinal waves Longitudinal wave- a wave where the displacement takes place in the same direction. Physically, they are a compression of particles that propagates through the medium. Sound- an example of these waves. It is a fluctuation of density or pressure in a given medium. The more the particles in the medium interact, the faster the wave speed. The speed of sound is 340 m/s. The speed of sound in water is about 1,100 m/s. Humans can hear sounds between 20Hz and 20,000Hz. Sounds under 20Hz-infrasonic. Sounds above 20,000Hz-ultrasonic
21. Wave interference Superposition- addition of the amplitudes of the two waves(AKA wave interference). Constructive inteference- when two waves overlap such that their peaks are at the same position so their amplitudes combine as a result. Destructive interference- when two waves overlap such that the peak of one wave is at the same position as the trough of the other wave at the same time so that the amplitudes combine to make an amplitude of zero .
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