# Warm-Up Exercise for lecture 27

## Due 8:00 am, Tues, 8 Dec 09

Physics 105, Fall 2009

Enter your 3-digit class identification number:

Enter the last 4 digits of your BYU ID:

Did you complete the reading assignment? (Typically this means at least 20-30 minutes looking over the assigned sections of the book.)
☐ yes ☐ no

If two waves are shifted by ________, completely destructive interference will occur.
l/2
2l/3
l
2l

In a standing wave, the points that have the maximum vibration are called:
☐ nodes
☐ anti-nodes

You have two pipes which produce sound: one is open at both ends (like an organ pipe) and the other is open at only one end (like a panpipe). If the two pipes have the same length, the fundamental resonant frequency will be ____________ for the two.
☐ the same
☐ different

Ralph recently saw this bumper-sticker on a professor's car: "If this sticker is blue, you're driving too fast!" (True story: a professor at my previous university had the sticker on her car.) The sticker looks RED to him. He is confused. Can you explain the joke to Ralph? (Note: Light undergoes a Doppler effect similar to sound, although the precise equation is slightly different than the one for sound given in the textbook. Also, you need to know that red light and blue light both travel at c = 3´108 m/s, but red light has a longer wavelength than blue.)

The comments in the next next two boxes go into a big, mostly anonymous text file that I skim through before the morning lecture, using the comments to help me plan class discussion. ("Mostly anonymous", because I can track down who made what comment, but it takes some effort on my part to do so.) Therefore, if you really want to make sure I see your question/comment and answer it individually, you should send it to me via email and not through this form.

Which part of today's assignment was particularly hard or confusing? What would you like to spend extra time on in class?