10 minutes maximum! Can you do it in 5?

1. The Doppler effect causes a shift in some properties of waves. Which quantities on the right are affected?

• A. All three.
• B. I and II
• C. I and III
• D. II and III

I wavelength

II wave speed

III frequency

2. An ambulance is moving towards an observer. Which of the following changes occurs to the sound wave heard by the observer?

 frequency wavelength A stays the same increases B increases decreases C decreases stays the same D decreases decreases

3. 'Red shift' is an effect seen in distant galaxies. White light is shifted towards the red end of the spectrum. This is explained by...

• A. the galaxy moving away from us, causing an increase in the wavelength.
• B. the galaxy moving towards us, causing an increase in the wavelength.
• C. the galaxy moving away from us, causing a decrease in the wavelength.
• D. the galaxy moving towards us, causing a decrease in the wavelength.

4.The formula on the right is used to calculate the frequency recorded by an observer. Which of the following best describes the use of this formula?

• A. Can be used for sound waves.
• B. Can only be used for light waves.
• C. Can only be used for a moving observer, not a moving source.
• D. Can only be used if source and observer are moving closer together

5+6. These questions are about choosing the correct formula.
The following formulas can be used to find the frequency of an observed source:

Which of the above formulas should be use if we are trying to find the frequency...

5. .. heard when an observer is standing still, and a fire engine is approaching at high speed?

6. .. from a house fire alarm whilst the observer is moving away in a car?

7-9. A radio wave of wavelength 100 m is emitted from a distant galaxy, travelling away from us at 10% the speed of light.

7. The observed wavelength will be approximately:

• A. 10 m
• B. 90 m
• C. 100 m
• D. 110 m

8. The observed speed of light will be:

• A. 0.1 c
• B. 0.9 c
• C. c
• D. 1.1 c

9. The observed frequency will be approximately:

10. The doppler effect can be used to find...

• A. the oxygen level in blood
• B. an image of a foetus in the womb using ultrasound
• C. the thickness of a thin film of glass or liquid
• D. the speed of a vehicle using radar