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Announcements 2/7/11

Announcements 2/7/11. Prayer About that exam… In Testing Center, Tues (tomorrow) until a week from Tues; late fee after 5 pm on last day Can bring handwritten 3x5 card (both sides) I will give you all constants/conversion factors/ materials parameters you need

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Announcements 2/7/11

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  1. Announcements 2/7/11 • Prayer • About that exam… • In Testing Center, Tues (tomorrow) until a week from Tues; late fee after 5 pm on last day • Can bring handwritten 3x5 card (both sides) • I will give you all constants/conversion factors/ materials parameters you need • See first page of last year’s exam • Can use your own calculator (but storing extra stuff in calc. memory violates spirit if not letter of the law) • Time goal: 2 hours avg (took me 33 mins)

  2. More on the exam • What to study? Well, especially… • Homework • Class notes • Old exams • Book • Some more specifics about the exam

  3. Foxtrot

  4. Waves • Skipping: Oscillations, Ch. 15 • Today: Basic wave info • Starting Wednesday: Some sections from Physics Phor Phynatics, Dr. Durfee’s book • Starting Friday: Complex numbers • Clicker: Have you seen: eix = cosx + isinx ? A = “have seen” B = “not” C = “maybe, but I can’t remember”

  5. Reading quiz • Which of the following phenomena can NOT exhibit a combination of transverse and longitudinal waves? • sound waves in air • surface water waves • waves in the earth generated by an earthquake

  6. 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) = (x – 5t)2 • What is its “velocity”?

  7. 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” • What if you want wave to move right-to-left? • “Wave function”

  8. 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”

  9. Did you say “Slinky”? • The handing out of the slinkies • We have about 36 • There are 40 students registered for the class

  10. Web demo • http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

  11. 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

  12. Worked Problem • AM1320 KFAN broadcasts the Utah Jazz games at a frequency of 1320 kHz. (Check out www.jazzfanz.com.) Radio waves travel at the speed of light, 3  108 m/s. (a) What is the wavelength of the AM1320 radio waves? (b) What is the period?

  13. 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?

  14. 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! Any function that has “x-vt” will work! …or “x+vt”

  15. k and w • What’s the difference between these: • General form of cosine wave: …sometimes written as: • k = “wavevector”; w = “angular frequency” w = _______

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