6.) Topic 6 The Universe Flashcards
What can line emission spectra identify?
Different elements, since the spectra of each element is different and unique
What do substances do when they are very hot
They emit light
What is used to split light into its different wavelengths?
A diffraction grating
How did scientists identify the chemical composition of stars?
Observe the light they emitted through a spectroscope and compare the line absorption spectra with the spectra of known elements
What can light be viewed as?
Viewed as a continuous spectrum where wavelength and frequency gradually change
What is a line emission spectrum produced from?
From light emitted by an element in a hot gas
a) What can the line emission spectra of hot gases be used to identify?
b) What can the line emission spectra act like?
a) The elements present in the cloud
b) Line emission spectra can act like a chemical fingerprint
In an absorption spectra, when a gas cools, what does it absorb?
It absorbs the same frequencies of light that it would emit if hot.
What do absorbed frequencies appear as if a continuous spectrum of light is passed through a cool gas and why
Appear as dark lines as they are taken in by the gas cloud between the observer and the light source
If a sound source is moving towards the listener
a) What happens to the wavelength and waves
b) What happens to the pitch
a) Waves are squashed and wavelength is reduced
b) Pitch becomes higher
If a sound source is moving away from the listener
a) What happens to the wavelength and waves
a) What happens to the pitch
a) Waves are extended and wavelength is increased
b) Pitch becomes lower
Give an example of The Doppler Effect
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)
What is red shift?
An observed increase in the wavelength of light caused by the source moving away from the observer
What does red shift tell us
It tells us the galaxies are moving away from each other and because the galaxies are moving away, the light waves are stretched
a) Galaxies which are further away have a bigger or smaller red shift?
b) Are they moving faster or slower than galaxies closer?
a) Bigger
b) Faster
What happens when planets move towards the observer and what is it called?
Light wavelength is compressed so the light changes to be loser to the blue end of the spectrum. This is called blueshift
Who observed spectra from distant galaxies to demonstrate red shift?
Sir Edwin Hubble
What 2 things can be said about the motion and wavelength of emitted light from a galaxy, the further away it is?
1- The further away a galaxy, the faster it is moving
2- The further away a galaxy, the greater the observed increase in wavelength
What 2 things does red-shift provide evidence for?
- Provides evidence that the universe is expanding
- Supports the Big Bang theory
What does the Big Bang theory suggest?
It suggests that the entire universe started from a very small, hot and dense region in space
Compare the observed red-shift of 2 galaxies, one further away than the other
. The galaxy further away is travelling faster
. The observed red-shift is greater the further away the galaxy is
What did scientists observe to provide evidence that the universe is expanding at an even faster rate?
They observed the supernovae, which suggested that galaxies are moving away at an even faster rate
Prior to observations of supernovae, what was believed about the rate of expansion of the universe and why?
The rate of expansion was expected to occur at an even slower rate
It was thought that gravitational forces would cause this slowing down
What is CMBR?
Cosmic Microwave Background Radiation
What 2 things does CMBR provide further evidence for?
The Big Bang theory
Believed that CMBR originates from radiation produced in the Big Bang
A) What was initially released in the explosion (The Big Bang)
B) What is detected now?
A) High energy, short wavelength gamma radiation
B) Lower energy, longer wavelength microwave radiation
How does the existence CMBR support the expansion of the universe? x2
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
State 2 facts which help provide evidence for the Big Bang theory
Light form distant galaxies is red shifted
Scientists have discovered CMBR
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)
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]
State what is meant by ‘absorption spectra’ and explain how they can provide information about stars and galaxies (6 marks)
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]
