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Doppler effect
IGCSE revision
Question | Answer |
---|---|
Velocity = what? X frequency | Velocity = wavelength X frequency |
Units of frequency are? | Hertz Hz or kiloHertz kHz |
If the source of a wave comes towards you, Doppler makes the frequency.......? | Higher frequency when the source comes towards you. |
If the source of a wave goes away from you, Doppler makes the frequency.......? | Lower frequency when the source moves away. |
If the source of a wave comes towards you, Doppler makes the wavelength ...........? | Shorter wavelength if the source comes towards you. |
If the source of a wave moves away from you, Doppler makes the wavelength ...........? | Longer wavelength if the source moves away from you. |
Which kind of wave is used to measure blood speeds? | Ultrasound |
Which kind of wave is used to measure car speeds? | microwaves |
If the light from a galaxy has a red shift, which way is it moving? | Red shift means it is moving away from us. |
If the light from a star has a blue shift, which way is it moving? | Blue shift means it is moving towards us. |
Two galaxies both have red shifts in the light we get from them. Galaxy A has twice the red shift that B has. What does this tell you about the speed? | Twice the red shift means that galaxy A has twice the speed of B. |
What did Hubble discover about galaxy speeds and distances? | That for most galaxies the speed a galaxy moves away from us is proportional to its distance. |
What does speed of recession mean? | Speed something is moving away from observer. |
Hubble's Law is evidence that the universe is expanding. What did it start from? | The Universe started from the Big Bang and has been expanding ever since. |
What kind of radiation was around just after the Big Bang? | Very short wavelength gamma radiation. |
What has happened to the gamma radiation that was around at the start of the Universe? | As the universe has expanded the original Doppler effect has expanded to microwaves. |
What does CMBR stand for? | Cosmic Microwave Background radiation. |
Where does CMBR come from? | Everywhere, in all directions. |
What is CMBR evidence for? | CMBR is a second piece of evidence that supports the idea of the Big Bang. |
If CMBR is the second piece of evidence for Big Bang and universe expanding, what is the first? | Hubble's discovery - most galaxies moving away, speed of recession is proportional to distance. |
What is ultrasound? | Waves with a frequency that is above human hearing (over 20000 Hz) |
Blood, car and galaxy speeds. Which measurement does NOT rely on reflected waves? | Galaxy speeds are measured from the light the stars in the galaxy give out. |
Ultrasound, microwaves, light. Which two have the same speed? | Microwaves and light travel at the same speed. |
If ultrasound travels at 1500 m/s in blood, what is the wavelength of 300 000 Hz (300 kHz) waves? | wavelength = speed/frequency = 1500/300 000 = 0.005 metres = 5 mm. |
why do we use ultrasound, not audible sound, to measure blood speeds? | Wavelength of audible sound is too big for measurements inside body. |