The Doppler Effect

Question 1

What is the Doppler Effect?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

It increases

Question 4

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

Answer 4

It becomes lower

Question 5

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

Answer 5

Red end

“Red Shift”

Question 6

Describe Red Shift

Answer 6

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

Question 7

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

Answer 7

It decreases

Question 8

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

Answer 8

It becomes higher

Question 9

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

Answer 9

redder than the actual light emitted by the star

Question 10

Describe Blue Shift

Answer 10

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

Question 11

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

Answer 11

Blue end

“Blue Shift”

Question 12

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

Answer 12

star will look bluer than it actually is.

Question 13

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

Answer 13

How fast the star is moving away or towards us.

Question 14

Higher velocity means the waves are …. more

Answer 14

Higher velocity means waves are SHIFTED more

Question 15

In the Doppler Shift formula, what does λ mean?

Answer 15

Emitted wavelength

Question 16

In the Doppler Shift formula, what does f mean?

Answer 16

Emitted frequency

Question 17

In the Doppler Shift formula, what does Δλ mean?

Answer 17

Difference between emitted wavelength and observed wavelength

Question 18

In the Doppler Shift formula, what does Δf mean?

Answer 18

Difference between emitted frequency and observed frequency

Question 19

In the Doppler Shift formula, what does v mean?

Answer 19

Recessional velocity

Question 20

When is v positive and when is it negative?

Answer 20

Source moving away V is negative.

Source moving towards observer V is positive

Question 21

When is Z negative

Answer 21

If red shift is negative = moving towards = blue shift

Question 22

What is recessional velocity?

Answer 22

How fast the source is moving AWAY from the observer

Question 23

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

Answer 23

Still red and blue shift

Question 24

In the Doppler Shift formula, what does z mean?

Answer 24

The amount of Red/Blue Shift

Question 25

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

Answer 25

Question 26

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

Answer 26

Question 27

What is Δf?

Answer 27

Observed frequency - emitted frequency

Question 28

When is Δf is negative and when is it positive?

Answer 28

Question 29

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

Answer 29

Question 30

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

Answer 30

Cosmological red shift: | Space itself is expanding. Light waves are being stretched with it

Question 31

What does HBB stand for?

Answer 31

Hot Big Bang Theory

Question 32

What is the Hot Big Bang Theory?

Answer 32

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

Question 33

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

Answer 33

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.

Question 34

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

Answer 34

Space itself is expanding and waves are stretched with it.

Question 35

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

Answer 35

Cosmological Red Shift

Question 36

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

Answer 36

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

Question 37

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

Answer 37

About half

Question 38

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

Answer 38

Lines in their spectra show a binary star system | Two separate lines (one Blue Shift, one Red Shift)

Question 39

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

Answer 39

Spectroscopic binary stars

Question 40

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

Answer 40

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

Question 41

Answer 41