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Join the exam review session this afternoon in Room C460 at 4 pm to prepare for the upcoming physics exam. No textbook or notes allowed, but you will be provided with a list of equations and necessary materials. Use your own calculator but do not store extra information in its memory. No time limit, but aim for an average time of 2 hours. Study homework, class notes, and old exams in preparation.
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Announcements 9/30/11 • Prayer • About that exam… • Review session this afternoon, 4 pm, room C460 • In Testing Center, Saturday morning until Thursday evening • No textbook, no notes • I will give you a list of equations (but not all equations!), and all constants/conversion factors/materials parameters you need • Can use your own calculator, but you’re on your honor not to store extra stuff in calc. memory • No time limit, but “time goal” is 2 hours avg (took me 33 mins)
More on the exam • What to study? I’d recommend in this order: • Homework • Class notes • Old exams • Book Chris office hours today: 3-4 pm Some more specifics about the exam… xkcd
Waves • Skipping: Oscillations, Ch. 15 • If you don’t recall “simple harmonic motion”, please review on your own. • Starting next lecture: Some sections from Physics Phor Phynatics, Dr. Durfee’s book • Starting lecture after that: Complex numbers • Clicker: Have you seen: eix = cosx + isinx ? A = “have seen” B = “not” C = “maybe, but I can’t remember”
Reading quiz • Which of the following phenomena do NOT exhibit a combination of transverse and longitudinal waves? • sound waves in air • surface water waves • waves in the earth generated by an earthquake
Wave intro: some math • What do these functions look like? • f(x) = x2 • f(x) = (x – 1)2 • Think: What would be an equation for a parabola that moves 1 m to the right every second? • What will this function look like at 0 s? at 1 s? at 2 s? • f(x) = (2x – 6t)2 • What is its “velocity”?
Sinusoidal waves • Nothing special about parabolas… • What does f(x) = cos(x – vt) look like at t = 0? at t = a little later? • Add in “amplitude” • Add in “phase” • How to change spatial period? • What if you want wave to move right-to-left instead of left-to-right? “Wave function”
Wave properties • Definition: oscillating disturbance that transfers energy (but not mass). • Direction of travel • Direction of oscillation: transverse vs longitudinal • Medium • Examples… • Water • Earthquake (P & S) • Sound • Light • Rubber tubing (demo) • Slinky (demo) Wikipedia: “S-wave”
Did you say “Slinky”? • The handing out of the slinkies • We have about 35 • There are 34 students registered for the class
Web demo • http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html
Wave properties, cont. • Web demo: Stokes’ “Traveling Sine Wave” http://stokes.byu.edu/sinewave_script_flash.html • Wavelength l • meters/wave • Period T • seconds/wave • Frequency ( f = 1/T ) • waves/second • Speed v • m/s v = fl
Wavefunction • Let’s call it “s(x)” for now (because “f” is used for frequency) • What are the units of s? • What does s really represent? • For transverse waves… • For longitudinal waves… • What does s(x) represent?
What’s that funny symbol? The (Linear 1D) Wave Equation • Why is it called the wave equation? • Because traveling waves are solutions of the equation! C = v2 Any function that has “x-vt” will work! …or “x+vt”
k and w • What’s the difference between these: • General form of cosine wave: …sometimes written as: • k = “wavevector”; w = “angular frequency” w = _______