6.) Topic 6 The Universe

Question 1

What can line emission spectra identify?

Answer 1

Different elements, since the spectra of each element is different and unique

Question 2

What do substances do when they are very hot

Answer 2

They emit light

Question 3

What is used to split light into its different wavelengths?

Answer 3

A diffraction grating

Question 4

How did scientists identify the chemical composition of stars?

Answer 4

Observe the light they emitted through a spectroscope and compare the line absorption spectra with the spectra of known elements

Question 5

What can light be viewed as?

Answer 5

Viewed as a continuous spectrum where wavelength and frequency gradually change

Question 6

What is a line emission spectrum produced from?

Answer 6

From light emitted by an element in a hot gas

Question 7

a) What can the line emission spectra of hot gases be used to identify?
b) What can the line emission spectra act like?

Answer 7

a) The elements present in the cloud

b) Line emission spectra can act like a chemical fingerprint

Question 8

In an absorption spectra, when a gas cools, what does it absorb?

Answer 8

It absorbs the same frequencies of light that it would emit if hot.

Question 9

What do absorbed frequencies appear as if a continuous spectrum of light is passed through a cool gas and why

Answer 9

Appear as dark lines as they are taken in by the gas cloud between the observer and the light source

Question 10

If a sound source is moving towards the listener

a) What happens to the wavelength and waves
b) What happens to the pitch

Answer 10

a) Waves are squashed and wavelength is reduced

b) Pitch becomes higher

Question 11

If a sound source is moving away from the listener

a) What happens to the wavelength and waves
a) What happens to the pitch

Answer 11

a) Waves are extended and wavelength is increased

b) Pitch becomes lower

Question 12

Give an example of The Doppler Effect

Answer 12

Sound of ambulance siren.
As it approaches, the sound appears in a higher pitch (shorter wavelength), and when it moves away, there is a lower pitch (longer wavelength)

Question 13

What is red shift?

Answer 13

An observed increase in the wavelength of light caused by the source moving away from the observer

Question 14

What does red shift tell us

Answer 14

It tells us the galaxies are moving away from each other and because the galaxies are moving away, the light waves are stretched

Question 15

a) Galaxies which are further away have a bigger or smaller red shift?
b) Are they moving faster or slower than galaxies closer?

Answer 15

a) Bigger

b) Faster

Question 16

What happens when planets move towards the observer and what is it called?

Answer 16

Light wavelength is compressed so the light changes to be loser to the blue end of the spectrum. This is called blueshift

Question 17

Who observed spectra from distant galaxies to demonstrate red shift?

Answer 17

Sir Edwin Hubble

Question 18

What 2 things can be said about the motion and wavelength of emitted light from a galaxy, the further away it is?

Answer 18

1- The further away a galaxy, the faster it is moving

2- The further away a galaxy, the greater the observed increase in wavelength

Question 19

What 2 things does red-shift provide evidence for?

Answer 19

• Provides evidence that the universe is expanding

- Supports the Big Bang theory

Question 20

What does the Big Bang theory suggest?

Answer 20

It suggests that the entire universe started from a very small, hot and dense region in space

Question 21

Compare the observed red-shift of 2 galaxies, one further away than the other

Answer 21

. The galaxy further away is travelling faster

. The observed red-shift is greater the further away the galaxy is

Question 22

What did scientists observe to provide evidence that the universe is expanding at an even faster rate?

Answer 22

They observed the supernovae, which suggested that galaxies are moving away at an even faster rate

Question 23

Prior to observations of supernovae, what was believed about the rate of expansion of the universe and why?

Answer 23

The rate of expansion was expected to occur at an even slower rate

It was thought that gravitational forces would cause this slowing down

Question 24

What is CMBR?

Answer 24

Cosmic Microwave Background Radiation

Question 25

What 2 things does CMBR provide further evidence for?

Answer 25

The Big Bang theory

Believed that CMBR originates from radiation produced in the Big Bang

Question 26

A) What was initially released in the explosion (The Big Bang)

B) What is detected now?

Answer 26

A) High energy, short wavelength gamma radiation

B) Lower energy, longer wavelength microwave radiation

Question 27

How does the existence CMBR support the expansion of the universe? x2

Answer 27

It is thought that gamma radiation was released in the Big Bang

The expansion of the universe has stretched this radiation, resulting in the microwave radiation present today

Question 28

State 2 facts which help provide evidence for the Big Bang theory

Answer 28

Light form distant galaxies is red shifted

Scientists have discovered CMBR

Question 29

Discuss the evidence for the Big Bang theory. Include in your answer reference to the following:

.Cosmological red shift of spectra from distant stars and galaxies

.CMBR

(6 marks)

Answer 29

Mark scheme:

Absorption spectra from distant galaxies consist of coloured light crossed with black lines. [1]

The wavelengths of the black lines are shifted to the red end of the spectrum when compared with light from similar sources in the laboratory. [1]

The black lines from more distant galaxies are more red-shifted, due to the expansion of space
itself. [1]

This suggests that the Universe began its existence at a single point and has expanded outwards
ever since. [1]

CMBR, on the other hand, initially existed as gamma radiation of very small wavelength but an expanding Universe has caused the wavelength to increase into the microwave region of the
electromagnetic spectrum. [1]

[+1 mark for correct spellings]

Question 30

State what is meant by ‘absorption spectra’ and explain how they can provide information about stars and galaxies (6 marks)

Answer 30

They are spectra of light crossed by dark lines. [1]

They can tell us the composition of the star/galaxy gas cloud because different elements absorb light at different wavelengths to produce each dark line. [1]

They can also tell us how far away the galaxy is from us …[1]

… and the further away from us, the faster the galaxy moves …[1]

… and the further the dark lines are red-shifted. [1]

[+1 mark for correct spellings]