Define Doppler effect .

The apparent shift in wavelength occurring when the source of the waves is moving relative to an observer.

How do wavefronts appear when a source moves towards an observer?

They appear squashed together, so the observed wavelength decreases and the frequency increases .

What happens to the waves emitted behind a moving source?

The wavelength increases (λ + Δλ) and the frequency decreases .

A stationary wave source produces wavefronts that spread out .......... .

A stationary wave source produces wavefronts that spread out symmetrically .

True or False? A moving source changes the actual wavelength it emits.

False. The actual wavelength emitted by the source stays the same . Only the wavelength received by the observer appears to change.

Light from a distant galaxy is shifted towards the red end of the spectrum. What does this provide evidence for?

That the universe is expanding .

Which type of radiation can the Doppler effect be observed with?

Any form of electromagnetic radiation .

The fractional increase in wavelength (or decrease in frequency ) due to the source and observer receding from each other.

What is the difference between redshift and blueshift ?

Redshift occurs when an object is moving away from Earth; blueshift occurs when it is moving towards Earth.

True or False? A redshifted spectral line means the light of that line has turned red.

False. Redshift means the wavelength of the spectral lines increases towards the red end of the spectrum. The lines themselves do not become red.

Hubble's law states that the recessional velocity of a galaxy is .......... to its distance from Earth.

Hubble's law states that the recessional velocity of a galaxy is proportional to its distance from Earth.

How does a galaxy's recessional speed depend on its distance from Earth?

The further away a galaxy is, the faster it moves away from us.

Matter which cannot be seen and that does not emit or absorb electromagnetic radiation .

What is the latest estimate of the Hubble constant from Planck satellite data?

67.4 ± 0.5 km s -1 Mpc -1 (Planck Collaboration, 2020).

How can the Hubble constant be found from a graph of recessional velocity against distance?

It is the gradient of the straight line through the origin.

We would expect an object's velocity to .......... as it moves further from a galaxy's centre, because the gravitational field strength weakens.

We would expect an object's velocity to decrease as it moves further from a galaxy's centre, because the gravitational field strength weakens.

How is dark matter detected, given that it cannot be seen directly through telescopes?

Through its gravitational effects — the rotation of galaxies and the gravitational lensing of starlight.

True or False? In a galaxy, stars further from the centre orbit more slowly, just like the outer planets of the solar system.

False. Unlike the solar system, stars in the outer regions of a galaxy do not slow down as expected. This anomaly is evidence for dark matter .

A LevelPhysicsEdexcelFlashcards10. SpaceCosmology

Cosmology (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

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FrontDoppler Shift
Define Doppler effect.

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Cards in this collection (21)

Define Doppler effect.
The apparent shift in wavelength occurring when the source of the waves is moving relative to an observer.
How do wavefronts appear when a source moves towards an observer?
They appear squashed together, so the observed wavelength decreases and the frequency increases.
What happens to the waves emitted behind a moving source?
The wavelength increases (λ + Δλ) and the frequency decreases.
A stationary wave source produces wavefronts that spread out ...........
A stationary wave source produces wavefronts that spread out symmetrically.
True or False?
A moving source changes the actual wavelength it emits.
False.
The actual wavelength emitted by the source stays the same. Only the wavelength received by the observer appears to change.
Light from a distant galaxy is shifted towards the red end of the spectrum. What does this provide evidence for?
That the universe is expanding.
Which type of radiation can the Doppler effect be observed with?
Any form of electromagnetic radiation.
Define redshift.
The fractional increase in wavelength (or decrease in frequency) due to the source and observer receding from each other.
What is the difference between redshift and blueshift?
Redshift occurs when an object is moving away from Earth; blueshift occurs when it is moving towards Earth.
State the Doppler redshift equation for a non-relativistic galaxy.
$\frac{Δ λ}{λ} = \frac{Δ f}{f} = \frac{v}{c}$
where v = speed of recession and c = speed of light in a vacuum.
True or False?
A redshifted spectral line means the light of that line has turned red.
False.
Redshift means the wavelength of the spectral lines increases towards the red end of the spectrum. The lines themselves do not become red.
Hubble's law states that the recessional velocity of a galaxy is .......... to its distance from Earth.
Hubble's law states that the recessional velocity of a galaxy is proportional to its distance from Earth.
State Hubble's law as an equation, defining each term.
$v \approx H_{0} d$
where v = recessional velocity (km s^-1), H₀ = Hubble constant (km s^-1 Mpc^-1) and d = distance from Earth (Mpc).
How does a galaxy's recessional speed depend on its distance from Earth?
The further away a galaxy is, the faster it moves away from us.
Define dark matter.
Matter which cannot be seen and that does not emit or absorb electromagnetic radiation.
How is the Hubble constant related to recessional velocity and distance?
$H_{0} = \frac{v}{d}$
where v = recessional velocity (km s^-1) and d = distance from Earth (Mpc).
What is the latest estimate of the Hubble constant from Planck satellite data?
67.4 ± 0.5 km s^-1 Mpc^-1 (Planck Collaboration, 2020).
How can the Hubble constant be found from a graph of recessional velocity against distance?
It is the gradient of the straight line through the origin.
We would expect an object's velocity to .......... as it moves further from a galaxy's centre, because the gravitational field strength weakens.
We would expect an object's velocity to decrease as it moves further from a galaxy's centre, because the gravitational field strength weakens.
How is dark matter detected, given that it cannot be seen directly through telescopes?
Through its gravitational effects — the rotation of galaxies and the gravitational lensing of starlight.
True or False?
In a galaxy, stars further from the centre orbit more slowly, just like the outer planets of the solar system.
False.
Unlike the solar system, stars in the outer regions of a galaxy do not slow down as expected. This anomaly is evidence for dark matter.

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