Special Things About a Light Wave It does not need a medium through which to travel Its highest velocity is the speed of light, c, equal to 300,000 km/sec (or 3 X10 8 m/s) The frequency (or wavelength) of the wave determines whether we call it radio, infrared, visible, ultraviolet, X-ray or gamma-ray.
Wave Speed Wavelength is distance between peaks Frequency is number of peaks per second going past a point in the water Frequency depends on wavelength and how fast the wave moves!!!
Wave Properties Wavelength Wavelength: The distance between identical points on the wave. Amplitude A l Amplitude: The maximum displacement A of a point on the wave. A
PERIOD wave period : the time that elapses between the passage of two successive wave crests past a fixed point Ex. if frequency is 17, means 17 waves passed in a second, so each wave has a period of 1/17 of that second.
Transmission of energyTransmission of energy ReflectionReflection RefractionRefraction DiffractionDiffraction InterferenceInterference
reflected A travelling wave is reflected when it hits a barrier. This phenomenon can easily be observed when a travelling water wave hits a reflector in the ripple tank. Reflection of Waves Reflected waves Reflecto r
Wave Reflection Think of arrows pointing in the direction of the wave motion We can trace the path of these arrows Angles Equal
Wave Reflection Acoustics of room design is very interesting. Need some reflections to “liven” the room. Too many reflections and the sound gets mushy. Look in a concert hall or auditorium to see the different sound treatments
Diffraction of Waves. When a travelling water wave hits an obstacle, the wave fronts spreads out round the edge and becomes curved. This phenomenon refers to diffraction. The wavelength of the wave is not changed in diffraction.
Interference of Waves interference When two or more waves propagating in the same medium meet at the same point, interference is said to occur. A stable interference pattern can be observed when two water waves of same frequency meet one another in a ripple tank. + =
Interference Constructive interference – the waves combine into a bigger wave. Destructive – one wave subtracts – so you get a smaller wave.
Standing Waves Recall from the discussion of wave interactions that waves can be reflected when they encounter a boundary. When that happens, the wave flips over and heads back in the opposite direction. So far, so good.
Now suppose that a whole series of waves are introduced into the medium. The incoming waves will meet up with the reflected waves. The result might be a jumbled mess. But if the frequency of the wave is just right, an interesting pattern will emerge.
Some points on the medium will move up and down with very large amplitudes. These are called ANTINODES. Other points on the medium will not move at all. These are called NODES. This pattern we are describing is called a STANDING WAVE
If a standing wave is established in a rope, and Frieda the fly were sitting on a node, she would not feel the rope move. On the other hand, her boyfriend Frankie the flea who's sitting on an antinode, will be in for the ride of his life.