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

Homework: PS 13, Chapter 15, is due Wed. at 11PMClicker question feedback:

see WebAssign ForumRe-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/

A. PH 105-003/4 ---- Monday, Nov. 26, 2007A. Homework: B. PS 14, Chapter 16 (short), due Wed. at

11PMC. Clicker question feedback: 4 responsesD. Problem Session: Weds. 5 PM (Jones

Th@5?)

E. Exam Friday: F. Ch. 13.3 (Kepler) – Ch. 19.5 (ideal

gas)G. [may skip 19.4, thermal expansion]

Chapter 17: I = intensity = power/area10-12 w/m2 = ideal threshold of hearing10-7 w/m2 = conversationuse log scale“sound level” = 10 log10 I/I0

A. PH 105-003/4 ---- Monday, Nov. 26, 2007

= I0

(units decibels) e.g., I/I0 = 100,000 ↔ = 50 decibels

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

40

1

Threshold of hearing

w/ left aid on high

depends on frequency – but is about 10-12 watts for a range of frequencies (50 Hz – 12KHz).Free wwwhearing test:

Chapter 17: Point source: Total power P = area*I

P = 4r2 I I=?

r

PH 105-003/4 ---- Monday, Nov. 26, 2007

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

Chapter 17: Doppler Effect moving source and/or observer

Active Figure 17.8Apparent frequency (heard by observer):

A. PH 105-003/4 ---- Monday, Nov. 26, 2007

fvv

vvf

source

observer'

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

A. Less than 500 Hz

B. Exactly 500 Hz

C. More than 500 Hz

Solution: Plug into equation:vs = +85 mph (toward observer)vo = -85 mph (away from source)

A. PH 105-003/4 ---- Monday, Nov. 26, 2007

fvv

vvf

source

observer'

fv

v

)mph 85(

)mph 85(

Hz 500 f

Solution: Plug into equation:vs = +85 mph (toward observer)vo = -85 mph (away from source)

A. PH 105-003/4 ---- Monday, Nov. 26, 2007

fvv

vvf

source

observer'

fv

v

)mph 85(

)mph 85(

Hz 500 f

Chapter 18: Standing waves.Review: On a string of length L, there can

be n half-wavelengths: L = n /2, so n = 2L/nResulting frequencies: fn = v/nn v/2L = n f1

In an air column, closed end displacement node2 closed ends: like string, f = f1, 2f1, 3f1, ...

open end pressure node displacement antinode

One open, one closed: L = n /2 + /4f = f0, 3f0, 5f0, …

A. PH 105-003/4 ---- Monday, Nov. 26, 2007

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

Exam backHomework due FridayClosing assessment WednesdayChapter 18.5: Beats Active Figure 18.17

fbeat = f2 – f1

Chapter 19: Temperature

A. PH 105-003/4 ---- Monday, Dec. 3, 2007

[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

A. Very good idea

B. Good idea

C. No opinion

D. Bad idea

E. Very bad idea