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Packet #5. Transmitted Properties & Refraction. When a wave is transmitted, the FREQUENCY stays constant. Example 1: Wavelength ( ) shortened, so the speed must have decreased. When a wave is transmitted, the FREQUENCY stays constant.
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Packet #5 Transmitted Properties & Refraction
When a wave is transmitted, the FREQUENCY stays constant. Example 1: Wavelength () shortened, so the speed must have decreased. When a wave is transmitted, the FREQUENCY stays constant. Example 2: Wavelength () lengthened, so the speed must have increased.
Equations & Relationships**** • If the medium is CONSTANT, then the speed (v) is CONSTANT. Wavelength and frequency have an indirect relationship. • v = f or v = f • If the medium is CHANGING, then the frequency (f or ) is CONSTANT. Speed and wavelength have a direct relationship. • v = f or v = f const const const const
A picture of water in a “ripple tank”: The wavelength () obviously shortened, so the speed must have _____ (increased or decreased?)
But, what if the new medium is at an angle? Then the wave bends. This is called refraction, when “a wave bends because of a medium change”.
Self-Check Questions • What happens to the frequency, wavelength, and speed of a wave as it is transmitted into a new medium? • What is refraction? (also see book page 391) • Do waves of different frequency refract differently? (The answer is yes! A primary example is the color spectrum, as seen below.) • Which color bends or refracts more? R O Y G B I V
When waves “interfere with each other during that split-second they interact/overlap, we use the Principle of Superposition: “the displacement of a medium caused by two or more disturbances is the algebraic sum of the displacements caused by the individual waves.” (In other words, you add the amplitudes.) Depending on whether you get a bigger amplitude, or smaller amplitude, you have constructive interference or destructive interference…… (You may also want to look at the pictures in your book on page 388 for some examples.)
Note, that in the case below, you will still get CONTRUCTIVE Interference, as the amplitude is getting bigger, albeit in the bottom!
Self-Check Questions • Do waves pass through or bounce off? • What is the (simple) Principle of Superposition? • What is destructive interference? • Draw out two examples: • Pulses +1 and 1 • Pulses 1 and +1 • What is constructive interference? • Draw out two examples: • Pulses +1 and + 1 • Pulses 1 and 1
11. Do page 398-399 #84 and #87 (**on test) 12. Tell whether each of the three cases in #84, and each of the four cases in #87, is constructive or destructive. (Note: #84 wave 3 is “partially destructive”.)
Standing Waves …. Standing waves are produced by constructive & destructive interference. ***A wave is reflected off of a much more dense medium, so that it is mostly reflected, and reflects inverted. The length between the source and reflection point must be a VERY specific amount! …...
Example 1: length is one-half a wavelength Example 2: length is two-halves a wavelength Example 3: length is three-halves a wavelength
Do you get it? The length between the source and the reflection point has to be EXACTLY a number times half the wavelength.Lengthsource to reflection = (whole #) ·(½ )
Nodes & Antinodes …. How many nodes and antinodes does each example have? Answer: ex 1 (length = 1/2): 2 nodes, and 1 antinode ex 2 (length = 2/2): 3 nodes, and 2 antinodes ex 3 (length = 3/2): 4 nodes, and 3 antinodes
Nodes/Antinodes & Interference: • So, what kind of interference happens at nodes? (destructive) • So, what kind happens at antinodes? (constructive)
Music Application:
Self-Check Questions • **How are standing waves produced? (length between reflection point and source has to be _____; reflection point has to be ____ so that a) _____ and b) _____ happen.) • Draw a picture with 5 nodes and 4 antinodes. • Label the nodes & antinodes • What kind of interference happens at each? • What “principle” do you use to figure out constructive & destructive interference? • (See book page 389 for more information.)
When you have one “slit” through which the wave passes, it is called “single-slit diffraction”. (On the test, you will have to label this picture with those exact words, AND define diffraction!) waves direction
If there are two slits, you get “double-slit diffraction”. The pattern gets interesting, because you get very complicated interactions. You use the “principle of superposition” and get constructive and destructive interference of the two waves spreading out from the two slits, which then produces nodes & antinodes (see next slide).
On the test, you will have to label on of these picture with the exact words “double-slit diffraction”, define diffraction, AND talk about how constructive and destructive interference are linked to double-slit diffraction. (Note - waves in both examples start from the left …)
Self-Check Questions • There are three very similar terms that have been covered: Reflection, Refraction, and Diffraction. It is extremely important that you keep them straight! ….. • Write out the 6 dots below on your paper. Fill in the underline for each. • Next to each phrase (dotted thing), you must draw ONE sketch of what that looks like (for a total of 6 sketches.) • Erect or inverted _____ (packet 4, slide 9 or 10) • law of _____ (packet 4, slide 13 or 14) • water waves bending due to _____ (packet 5, slide 5 or 6) • white light breaking up into colors due to _____ (packet 5, slide 7) • single-slit _____ (packet 5, slide 22 or 23) • double-slit _____ (packet 5, slide 24 or 25)
