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

Describe Blue Shift

Answer 9

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 10

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

Answer 10

Blue end

“Blue Shift”

Question 11

In the Doppler Shift formula, what does λ mean?

Answer 11

Emitted wavelength

Question 12

In the Doppler Shift formula, what does f mean?

Answer 12

Emitted frequency

Question 13

In the Doppler Shift formula, what does Δλ mean?

Answer 13

Difference between emitted wavelength and observed wavelength

Question 14

In the Doppler Shift formula, what does Δf mean?

Answer 14

Difference between emitted frequency and observed frequency

Question 15

In the Doppler Shift formula, what does v mean?

Answer 15

Recessional velocity

Question 16

What is recessional velocity?

Answer 16

How fast the source is moving AWAY from the observer

Question 17

In the Doppler Shift formula, what does z mean?

Answer 17

The amount of Red/Blue Shift

Question 18

What does HBB stand for?

Answer 18

Hot Big Bang Theory

Question 19

What is the Hot Big Bang Theory?

Answer 19

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

Question 20

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

Answer 20

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 21

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

Answer 21

Space itself is expanding and waves are stretched with it.

Question 22

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

Answer 22

Cosmological Red Shift

Question 23

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

Answer 23

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

Question 24

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

Answer 24

About half

Question 25

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

Answer 25

Lines in their spectra show a binary star system

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

Question 26

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

Answer 26

Spectroscopic binary stars

Question 27

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

Answer 27

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