U1.6 The expanding universe

Question 1

What does the Doppler Effect cause?

Answer 1

Shifts in wavelength of sound (and light)

Question 2

Explain the Doppler Effect.

Answer 2

The apparent shift in frequency is due to the wavelength changing, and the speed of the sound staying constant.

Question 3

When calculating observed or source frequency (Doppler Effect) would you use a + or - if the object is moving TOWARDS you?

Answer 3

-

Question 4

When calculating observed or source frequency (Doppler Effect) would you use a + or - if the object is moving AWAY from you?

Answer 4

+

Question 5

A passenger is travelling in a car. The car honks the horn. Will the passenger experience the Doppler Effect? Explain your answer.

Answer 5

No. This is because they are moving at the same speed as their siren/horn.

Question 6

What is meant by the Redshift of a galaxy?

Answer 6

The change in wavelength divided by the
emitted wavelength. For slowly moving galaxies, redshift is the ratio of the recessional
velocity of the galaxy to the velocity of light.

Question 7

Does increasing Redshift increase observed wavelength or frequency?

Answer 7

Wavelength

Question 8

What can Hubble’s Law be used for?

Answer 8

To estimate the age of the Universe

Question 9

How is the age of the Universe calculated?

Answer 9

1/Hubble’s constant

Question 10

What does the gradient of the graph of recessional velocity / distance show?

Answer 10

The Hubble’s constant

Question 11

Describe the Big Bang theory.

Answer 11

The theory that at a moment in the past all matter in the Universe was contained rapidly outwards. This was the beginning of space and time.

Question 12

What led to the theory of the expansion of the Universe?

Answer 12

Measurements of the velocities of galaxies and their distance from us

Question 13

How can the mass of a galaxy be estimated?

Answer 13

By the orbital speed of stars within it

Question 14

Give evidence supporting the Big Bang Theory and subsequent expansion of the Universe.

Answer 14

The large number of galaxies showing redshift rather than blueshift,
Cosmic microwave background radiation,
Abundance of hydrogen and helium,
Olber’s paradox

Question 15

What is cosmic background radiation?

Answer 15

Radiation that has spread throughout the Universe from an early stage of its existence

Question 16

What is Olber’s paradox?

Answer 16

The apparent paradox that space appears to be black. It is no longer a paradox as it can be explained by the big bang.

Question 17

Where does evidence supporting the existence of dark matter come from?

Answer 17

Estimations of the mass of galaxies

Question 18

Where does evidence supporting the existence of dark energy come from?

Answer 18

The accelerating rate of expansion of the Universe

Question 19

What is a perfect black body?

Answer 19

An object that absorbs all the radiation that hits it

Question 20

What is the temperature of stellar objects related to?

Answer 20

The distribution of emitted radiation over a wide range of wavelengths.

Question 21

How does the peak wavelength of this distribution vary for hotter objects rather than cooler objects.

Answer 21

The peak wavelength is shorter.

Question 22

Do hotter or cooler objects emit more radiation per unit surface area per unit time?

Answer 22

Hotter