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# Doppler effect

### IGCSE revision

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.
Created by: waslancing

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