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AQA A-Level Astrophysics > The Doppler Effect > Flashcards

The Doppler Effect Flashcards

1
Q

What is the Doppler Effect?

A

The change in the frequency and wavelength of a wave due to movement of its source

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2
Q

Why do the frequency and wavelength of a wave with a moving source change?

A

The waves bunch together in front of the source and stretch out behind it

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3
Q

What happens to the wavelength of a wave when the source moves away from you?

A

It increases

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4
Q

What happens to the frequency of a wave when the source moves away from you?

A

It becomes lower

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5
Q

For a light source moving away from you, the change in frequency and wavelength shifts light to which end of the spectrum?

A

Red end

“Red Shift”

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6
Q

Describe Red Shift

A

As a light source moves away from an observer, the wavelength increases and frequency lowers. This shifts the light towards the red end of the spectrum

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7
Q

What happens to the wavelength of a wave when the source moves towards you?

A

It decreases

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8
Q

What happens to the frequency of a wave when the source moves towards you?

A

It becomes higher

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9
Q

What colour will the light from a star moving away from us appear as more?

A

redder than the actual light emitted by the star

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10
Q

Describe Blue Shift

A

As a light source moves towards an observer, the wavelength decreases and frequency increases. This shifts the light towards the blue end of the spectrum

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11
Q

For a light source moving towards you, the change in frequency and wavelength shifts light to which end of the spectrum?

A

Blue end

“Blue Shift”

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12
Q

What colour will the light from a star moving towards us appear as more?

A

star will look bluer than it actually is.

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13
Q

What does the amount of red or blue shift depend on?

A

How fast the star is moving away or towards us.

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14
Q

Higher velocity means the waves are …. more

A

Higher velocity means waves are SHIFTED more

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15
Q

In the Doppler Shift formula, what does λ mean?

A

Emitted wavelength

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16
Q

In the Doppler Shift formula, what does f mean?

A

Emitted frequency

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17
Q

In the Doppler Shift formula, what does Δλ mean?

A

Difference between emitted wavelength and observed wavelength

18
Q

In the Doppler Shift formula, what does Δf mean?

A

Difference between emitted frequency and observed frequency

19
Q

In the Doppler Shift formula, what does v mean?

A

Recessional velocity

20
Q

When is v positive and when is it negative?

A

Source moving away V is negative.

Source moving towards observer V is positive

21
Q

When is Z negative

A

If red shift is negative = moving towards = blue shift

22
Q

What is recessional velocity?

A

How fast the source is moving AWAY from the observer

23
Q

What is red and blue shift called if the wavelength is not visible light?

A

Still red and blue shift

24
Q

In the Doppler Shift formula, what does z mean?

A

The amount of Red/Blue Shift

25
Q

What will happen to a radiation spectrum of a moving source if it is red-shifted?
What does it look like?

A
26
Q

With absorption lines and a known frequency, how can you find redshift?

A
27
Q

What is Δf?

A

Observed frequency - emitted frequency

28
Q

When is Δf is negative and when is it positive?

A
29
Q

With absorption lines and a known wavelength, how can you find redshift?

A
30
Q

How to astronomers think red shift for all distant galaxies happens?

A

Cosmological red shift:

Space itself is expanding. Light waves are being stretched with it

31
Q

What does HBB stand for?

A

Hot Big Bang Theory

32
Q

What is the Hot Big Bang Theory?

A

The universe started off as an infinitely hot, infinitely dense singularity and has been expanding ever since

33
Q

What evidence does the Doppler Effect give for the Hot Big Band Theory?

A

The spectra from galaxies all show Red Shift (the characteristic spectral lines of the elements are longer than expected), meaning they’re all moving apart.

34
Q

Cosmologists don’t consider galaxies to be physically moving through space away from us. How do they explain Red Shift?

A

Space itself is expanding and waves are stretched with it.

35
Q

What is the theory that space itself is expanding called, in relation to Red Shift?

A

Cosmological Red Shift

36
Q

Why does the Red Shift of planets suggest that the universe started out as a single point?

A

The speed galaxies move away from us depends on how far away they are

37
Q

What proportion of stars we observe are actually two stars orbiting each-other?

A

About half

38
Q

How do we know that there are two stars when they are too far away to be resolved with telescopes?

A

Lines in their spectra show a binary star system

Two separate lines (one Blue Shift, one Red Shift)

39
Q

What do we call a binary star system that has been identified by its line spectra?

A

Spectroscopic binary stars

40
Q

How can the orbital period of a binary star system be calculated?

A

By observing how the absorption lines in the spectrum change with time
The time between maximum Blue Shift and maximum Red Shift

41
Q
A

AQA A-Level Astrophysics (11 decks)

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