Astronomy – Doppler Effect Quiz with Answers Name ___________________________________
Circle the correct answer. Be sure that you can explain why your answer is correct. Hand in this quiz by the NEXT class. Also work the Doppler tutorial but do not hand in the tutorial.
1. A car horn blares as it comes toward you and passes you at constant speed. The VOLUME of the horn: a. sounds louder and louder as the source approaches and sounds fainter and fainter as the source recedes
[I am referring to the sound you would hear standing by the side of the road. As the horn gets closer it sounds louder and louder and as the horn recedes it sounds fainter and fainter. Note this is not the Doppler
Effect.] b. stays at a constant loudness as the source approaches then drops to a fainter but constant loudness as the source recedes c. stays at the same constant loudness throughout the motion d. varies too much to tell what the volume is doing
2. As the horn passes by you at constant speed, the PITCH of the horn a. gets higher and higher as the source approaches and gets lower and lower as the source recedes b. stays at a constant high pitch as the source approaches and then drops to a constant lower pitch as the source recedes [The motion of the car compresses the waves ahead of the car so you hear a high pitch as the car approaches and a lower pitch as the car recedes.] c. stays at the same constant pitch throughout the motion d. maintains the same pitch except at the moment the source passes e. varies too much to tell what the pitch is doing
3. (Mark all that apply.) Which of the following statements is correct? a. The Doppler Effect is the change in volume of a source as it passes you. b. The Doppler Effect is the change in pitch of a source as it passes you. c. The Doppler Effect is the change in frequency of a source as it passes you. d. The Doppler Effect is the change in wavelength of a source as it passes you.
4. A source moves to the right. What will the observer shown on the right detect?
* X
Source moving

Observer a. longer wavelengths than an observer who stands to the left of the source b. shorter wavelengths than an observer who stands to the left of the source c. the same wavelengths no matter which side the observer stands on

5. A source moves to the right toward an observer as shown below. What will happen to the wavelengths if the source moves faster? a. Wavelengths on both sides of the source become shorter.
( ( ( ( * ) ) ) ) X
Source moving

Observer b. Wavelengths on both sides of the source become longer.
( ( ( ( * ) ) ) ) X
Source moving

Observer c. Wavelengths become longer on the side toward which the source moves but shorter on the other side.
( ( ( ( * ) ) ) ) X
Source moving

Observer d. Wavelengths become shorter on the side toward which the source moves but longer on the other side.
( ( ( ( * ) ) ) ) X
Source moving

Observer e. You can’t fool me, the wavelengths don’t change even if the source is moving.

Use the diagram below to answer questions 6 through 10 that follow:
Spectrum of element Xo at rest in lab
λ = 546 nm λ = 643 nm
↓ ↓
| | |
Spectrum of star A | | | ||
Spectrum of star B | | | |||||
6. From the spectra above, you can conclude that star A a. Contains the element Xo and only that element b. Contains the element Xo and at least one more element
[Xo’s pattern can be seen in star A’s spectrum. Therefore star A contains element Xo. But there are more lines in star A’s spectrum so star A contains at least one other element besides Xo.] c. Does not contain the element Xo d. There is not enough information to determine the composition
7. From the spectra above, you can conclude that star B a. Contains the element Xo and only that element b. Contains the element Xo and at least one more element c. Does not contain the element Xo d. There is not enough information to determine the composition
8. From the spectra above, you can conclude that Earth and star A a. Are moving toward each other b. Are moving away from each other
[The lines in star A’s spectrum are shifted toward longer wavelengths, a red shift. Therefore, star A and
Earth are moving away from each other.] c. There is not enough information to determine the direction of motion of Earth and star.
9. From the spectra above, you can conclude that Earth and star B a. Are moving toward each other
[The lines in star B’s spectrum are shifted toward shorter wavelengths, a blue shift. Therefore, star B and
Earth are moving toward each other.] b. Are moving away from each other c. There is not enough information to determine the direction of motion of Earth and star.
10. From the spectra above, you can conclude that a. Star A moves faster than star B
[The lines in star A’s spectrum are shifted more toward the red end than the lines in star B’s spectrum are shifted toward the blue end. Bigger shift means faster. Red shift tells you moving away and blue shift tells you moving toward BUT the amount of shift tells you how fast.] b. Star B moves faster than star A c. There is not enough information to determine the speeds.

11. What causes light from a star to be Doppler-shifted? a. the distance between the star and us b. the gas and dust between the star and us c. the relative speed of the star and us
[Speed is the issue not distance. Consider a distant star and a nearby star both moving toward you. If they move at the same speed, both spectra would show the same blue shift in spectral lines. If the nearby star moves toward you faster than the distant star, the nearby star’s spectral lines will be blue-shifted more than the distant star. If the distant star moves faster, its spectral lines will be blue-shifted more. Bigger shift means faster.] d. the temperature difference between the star and us
12. What did Vera Rubin and her colleagues measure that led them to discover Dark Matter? a. Mass of a few bright stars and gas b. Speeds of galaxies moving away from us c. Revolution speeds of planets d. Rotation speeds of galaxies
[Galaxies look like the most of the mass is at the center of the galaxy. Therefore astronomers expected stars near the center to move faster than stars near the outskirts, like planets around the sun. But Vera found that stars near the edge moved fast which meant that there must be lots of unseen mass near the outer parts of a galaxy.] e. Distances of galaxies
Rev 23 October 2015