Target: 10 Questions in 10 minutes

An IB Physics data booklet is helpful

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

I. wavelength
II. wave speed
III. frequency
  • A. All three.
  • B. I and II
  • C. I and III
  • D. II and III

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 can be used - in certain circumstances - to calculate the doppler effect on the frequency and wavelength of waves.

${\Delta f \over f} = {\Delta \lambda \over \lambda} \approx {v \over c} $

Which of the following best describes the use of this formula?

  • A. Used when the velocity of source/observer is close to the wave speed
  • B. Used when the velocity of source/observer is much smaller than the wave speed
  • C. Can only be used for a moving observer, not a moving source.
  • D. Can only be used for a moving source, not a moving observer.

 

 

5+6. A space satellite is travelling towards the Sun at 3 x 105 ms-1. Red light emitted from the sun has a wavelength of 6 x 10-7 m. The wavelength of this light is different when observed by the satellite.

The speed of light can be taken as 3 x 108 ms-1.

  

5. What is the change in wavelength Δλ observed?

  • A. 6 x 10-10 m
  • B. 6 x 10-4 m
  • C. 3 x 10-10 m
  • D. 3 x 10-4 m

5. What is the change in frequency Δf observed?

  • A. 2 x 109 m
  • B. 2 x 1012 m
  • C. 5 x 108 m
  • D. 5 x 1011 m

 

7-9. A radio wave of wavelength 100 m is emitted from a distant galaxy, travelling away from us at 1% the speed of light.

 distant galaxy

7. The observed wavelength will be approximately:

  • A. 1 m
  • B. 9 m
  • C. 101 m
  • D. 99 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:

  • A. $ 1.01 \times {c \over 100} $
  • B. $ 0.99 \times {c \over 100} $
  • C. $ 101c $
  • D. $ 99c $

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. a break or fracture in a bone
  • D. the speed of blood flow in an artery