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PH 105-003/4 ----Monday, Nov. 19, 2007

PH 105-003/4 ----Monday, Nov. 19, 2007. Homework: PS 13, Chapter 15, is due Wed. at 11PM Clicker question feedback: see WebAssign Forum Re-do clicker question on scientific notation. Chapter 16: we’ll skip Sec. 16.4-5-6 (reflection, energy transfer, wave equation)

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PH 105-003/4 ----Monday, Nov. 19, 2007

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  1. PH 105-003/4 ----Monday, Nov. 19, 2007 Homework: PS 13, Chapter 15, is due Wed. at 11PM Clicker question feedback: see WebAssign Forum Re-do clicker question on scientific notation Chapter 16: we’ll skip Sec. 16.4-5-6 (reflection, energy transfer, wave equation) Chapter 17: Sound waves: Active Figure 17.2, v2 = B/r

  2. PH 105-003/4 ---- Monday, Nov. 26, 2007 • Homework: • PS 14, Chapter 16 (short), due Wed. at 11PM • Clicker question feedback: 4 responses • Problem Session: Weds. 5 PM (Jones Th@5?) • Exam Friday: • Ch. 13.3 (Kepler) – Ch. 19.5 (ideal gas) • [may skip 19.4, thermal expansion]

  3. PH 105-003/4 ---- Monday, Nov. 26, 2007 Chapter 17: I = intensity = power/area 10-12 w/m2 = ideal threshold of hearing 10-7 w/m2 = conversation use log scale “sound level” b = 10 log10 I/I0 = I0 (units decibels) e.g., I/I0 = 100,000 ↔ b = 50 decibels

  4. Clicker question (Nov 19): According to R. Serway, a mosquito buzz has intensity 10-8 w/m2. How many decibels is this? • 40 • 1

  5. Threshold of hearing depends on frequency – but is about 10-12 watts for a range of frequencies (50 Hz – 12KHz). Free wwwhearing test: w/ left aid on high

  6. PH 105-003/4 ---- Monday, Nov. 26, 2007 Chapter 17: Point source: Total power P = area*I P = 4p r2 I I=? r

  7. 2nd Clicker question (Nov 25): If the sound of a mosquito has intensity 10-8 w/m2 at a distance of 0.2 m, what is the total sound power produced by the mosquito, in nanowatts? • 5 • 0.5

  8. PH 105-003/4 ---- Monday, Nov. 26, 2007 Chapter 17: Doppler Effect moving source and/or observer Active Figure 17.8 Apparent frequency (heard by observer):

  9. Clicker Question: While you are traveling at 85 mph, a state trooper driving behind you (moving in the same direction) at 85 mph turns on his 500 Hz siren. The frequency you hear is • Less than 500 Hz • Exactly 500 Hz • More than 500 Hz

  10. PH 105-003/4 ---- Monday, Nov. 26, 2007 Solution: Plug into equation: vs = +85 mph (toward observer) vo = -85 mph (away from source)

  11. PH 105-003/4 ---- Monday, Nov. 26, 2007 Solution: Plug into equation: vs = +85 mph (toward observer) vo = -85 mph (away from source)

  12. PH 105-003/4 ---- Monday, Nov. 26, 2007 Chapter 18: Standing waves. Review: On a string of length L, there can be n half-wavelengths: L = n l/2, so ln = 2L/n Resulting frequencies: fn = v/ln = n v/2L = n f1 In an air column, closed end  displacement node 2 closed ends: like string, f= f1, 2f1, 3f1, ... open end  pressure node  displacement antinode One open, one closed: L = n l/2 + l/4 f = f0, 3f0, 5f0, …

  13. Sec. 18.6: 1D vs. 2D vibrations [or, why 1D objects (strings, horns) make music, while 2D objects (drumheads) make noise] Vibrations of 1D objects: fn = n f1 (integer ratios) Normal modes of a drumhead (Fig. 18.16) ½ # azimuthal nodes, # radial nodes frequency f Fig. 18-16, p. 517

  14. PH 105-003/4 ---- Monday, Dec. 3, 2007 Exam back Homework due Friday Closing assessment Wednesday Chapter 18.5: Beats Active Figure 18.17 fbeat = f2 – f1 Chapter 19: Temperature

  15. [Anonymous] Clicker question:It has been suggested that we have a “lab review” or “lab final” instead of the last lab this Thursday, in which each individual student would do one or two pieces of a previous lab. Rate this as a • Very good idea • Good idea • No opinion • Bad idea • Very bad idea

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