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Announcements 10/1/10

- Prayer
- Tutorial Lab only open 12-2 pm tomorrow
- Tomorrow = last day to register your clicker and still get credit for past quizzes. Look at your clicker right now… is one of these your number?

The Exam

- “What’s on the exam” handout
- Exam starts tomorrow in Testing Center (HGB). Anyone not know about the T.C.? See http://testing.byu.edu.
- T.C. opens tomorrow at 8 am.

- Exam ends next Saturday
- Correction to syllabus: on Saturdays, the Testing Center gives out last exam at 3 pm, closes at 4 pm.

- Can bring handwritten 3x5 card (both sides)
- I will give you all constants/conversion factors you need
- Can use your own calculator (storing stuff in calc memory violates spirit if not letter of the law)
- Time goal: 2 hours avg (took me 35 mins)

Demo

- “Adiabatic Cotton Burner”

Waves

- Skipping: Oscillations, Ch. 15
- Today: Basic wave info
- Next week: Detour to “Physics Phor Phynatics”, Dr. Durfee’s book
- For Monday, S&J 16.3-16.6; PpP 2.1, 2.2.
- 2.4.1 & 2.4.2 also recommended (but not 2.3 or 2.4.3)

- Wed = complex numbers. Quick survey via clickers:
- Do you know complex numbers fairly well?
A = “know fairly well”; B = “not”

- Have you seen: eix = cosx + isinx ?
A = “have seen”; B = “not”

- Do you know complex numbers fairly well?

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

Wave intro: some math

- What do these functions look like?
- f(x) = x2
- f(x) = (x – 1)2

- Quick writing: 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”?

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”

Wave properties

- Definition: oscillating disturbance that transfers energy (but not mass).
- Direction
- Medium
- Transverse vs Longitudinal
- 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 only have 34
- There are 46 students in 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
- m/wave

- Period T
- s/wave

- Frequency ( f = 1/T )
- waves/s

- Speed v
- m/s

v = fl

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?

Wavefunction

- Let’s call it “s(x)” (because “f” is used for frequency)
- What does s(x) represent?
- For transverse waves…
- For longitudinal waves…

- What does s(x) represent?

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”

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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