Week 3 Lecture 2
Solutions at the bottom.

1)  In-video quiz at timepoint 02:01.

"Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength."

http://www.qrg.northwestern.edu/projects/vss/docs/communications/1-what-is-wavelength.html

2)  In-video quiz at timepoint 03:42.

Which of the following equations is correct for finding the frequency (f) of a sound wave (or light wave)?

c = speed of the wave
⋋ = wavelength
A = amplitude of the wave

A) f = A² ⋋
B) f = c ⋋
C) f = c/⋋
D) f = ⋋/c

3)  In-video quiz at timepoint 13:01.

The speed of sound in air is roughly 340 m/s.  How fast does a noise source, like an airplane, have to move toward you for the wavelength of the sound to be half as long for a stationary observer than for a person in the airplane?  Give your answer in m/s rounded to two significant digits.

[Open-ended]

Solutions:

2) The correct answer is C) f = c/⋋

3) The correct answer is (160,180)

λ = λ0 ( 1 - v / c) 

From the problem statement, λ, the observed wavelength, is half of the value of λ0 the emitted wavelength.  Therefore (1 - v/c) = 0.5

Solving for v gives v=0.5 c.  With a known value for c of 340 m/s, the answer correct to two significant digits is v=170 m/s.