Lecture 8: Chapters 16, 32

Homework etc

• Homework folders will go around. Get homework 1, 2, 3. Homework 3 is returned for last names L and after only (but the grading is complete).
• If you did not bring your "paper clicker", get one from the front.

Doppler effect

You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of $f_0$, what frequency does your friend hear?

1. lower than $f_0$

2. equal to $f_0$

3. higher than $f_0$

Ans: C

Doppler effect

In the previous question, the horn had a rest frequency of $f_0$, and we found that your friend heard a higher frequency $f_1$ due to the Doppler shift. The sound from the boat hits the cliff behind your friend and returns to you as an echo. What is the frequency of the echo that you hear?

1. equal to $f_0$

2. higher than $f_0$ but lower than $f_1$

3. equal to $f_1$

4. higher than $f_1$

Ans: D

Doppler effect

Your friend is saying something to you, while there is a very fast wind blowing between you and your friend. Both you and your friend are at rest. Your friend is speaking at 500 Hz. The frequency of the sound that you hear is

1. less than 500 Hz
2. equal to 500 Hz
3. greater than 500 Hz

Ans: B

Doppler effect

Your friend is saying something to you, while there is a very calm air between you and your friend. Both you and your friend are at rest. Your friend is speaking at 500 Hz. Both you and your friend are running very fast at the same velocity. The frequency of the sound that you hear is

1. less than 500 Hz
2. equal to 500 Hz
3. greater than 500 Hz

Ans: B

Reflection

When watching the Moon over the ocean, you often see a long streak of light on the surface of the water. This occurs because

1. the Moon is very large
2. the Moon moves
3. the ocean is calm
4. the ocean is wavy

Ans: D

Reflection

Consider a spherical mirror. The focal length ($f$) can be defined as the image distance ($d_i$) of a very distant object. It is said that $f = r/2$, for a spherical mirror. The actual image of a distant object is

1. closer to the mirror than $r / 2$

2. always equal to $r / 2$ no matter what the height of the distant object is

3. farther way from the mirror than $r / 2$

Ans: A