9.3 CHAPTER 9. DOPPLEREFFECT
- The Doppler Effect canbe observed in all typesof waves, including ultrasound,
light and radiowaves. - Sonography makes useof ultrasound and the Doppler Effect to determine the
direction of blood flow. - Light is emitted by stars. Due to the DopplerEffect, the frequency ofthis light
decreases and the startsappear red. This is called a red shift and meansthat the
stars are moving away from the Earth. This means that the Universe is expanding.
Chapter 9 End of Chapter Exercises
- Write a definition foreach of the following terms.
(a) Doppler Effect
(b) Red-shift
(c) Ultrasound - Explain how the Doppler Effect is used to determine the direction of
blood flow in veins. - The hooter of an approaching taxi has a frequency of 500 Hz. If the
taxi is travelling at 30 m·s−^1 and the speed of soundis 300 m·s−^1 ,
calculate the frequencyof sound that you hear when
(a) the taxi is approaching you.
(b) the taxi passed youand is driving away. - A truck approachesyou at an unknown speed. The sound of the
trucks engine has a frequency of 210 Hz, however you hear a fre-
quency of 220 Hz. Thespeed of sound is 340 m·s−^1.
(a) Calculate the speedof the truck.
(b) How will the soundchange as the truck passes you? Explain this
phenomenon in termsof the wavelength andfrequency of the
sound. - A police car is driving towards a fleeing suspect at 35 v m.s−^1 , where
v is the speed of sound. The frequency of the police car’s siren is
400 Hz. The suspect is running away at 68 v. What frequency does the
suspect hear? - (a) Why are ultrasound waves used in sonography and not sound
waves?
(b) Explain how the Doppler effect is used to determine the direction
of flow of blood in veins.
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