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A Level Physics Paper 3 > Astrophysics: Extra > Flashcards

Astrophysics: Extra Flashcards

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1
Q

Minimum angular resolution

A

Resolving power
The minimum angular separation which the instrument can resolve/distinguish
Measured in radians

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2
Q

What does minimum angular resolution

A

How far away they are

How close they are

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3
Q

Why do telescopes not focus stars to a perfect point

A

Focus as an airy disc/pattern

Seen as the diffraction pattern from a point of light as the light waves diffract through the aperture of a telescope

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4
Q

Formula for minimum angular resolution assuming the limit is due to diffraction by the circular objective

A

Rayleigh criterion formula on formula sheet

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5
Q

Explain the Rayleigh criterion formula

A

Theta is the minimum angle that can be resolved in radians
Wavelength of light in metres
D is the diameter of the objective lens or primary mirror in metres

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6
Q

What is collecting power

A

An important parameter
A measure of its ability to collect incident electromagnetic radiation
Directly proportional to the square of the diameter

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7
Q

Black body

A

Perfect absorber and emitter of electromagnetic radiation
Absorbs all the EM radiation that falls on it
And a perfect emitter

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8
Q

What is a spectrum

A

A graph of intensity against wavelength or frequency

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9
Q

What is the area of an intensity wavelength graph

A

How much energy is emitted for the wavelengths

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10
Q

What can be said about the total amount of radiation from a body when the temperature increases

A

Total amount of radiation increases

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11
Q

Explain the graph for Wein’s displacement law

A

Wavelength max on y
Temperature of x
Inversely proportional

Hotter stars will produce more light at the blue/violet end of the spectrum and will appear bluer or blue-white
Cooler stars look red as they produce more of their light at longer wavelengths

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12
Q

Assumptions made for Wein’s displacement law

A

No radiation is absorbed in space/by earths atmosphere

Assume to be a perfect black body

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13
Q

Why might ground-based observations of stars lead to erroneous conclusions regarding the temperature

A

Space is better because less impediment to radiation so gives a lower maximum wavelength
Atmosphere not equally transported to all wavelengths

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14
Q

Stefan’s law

A

Relates the total power output, P, of a star to its black body temperature, T, and its surface area, A

Tells you if two stars have the same black body temperature (are the same spectral class), the star with the brighter absolute magnitude has the larger diameter

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15
Q

Ratio equation for power output against diameter for two black bodies

A

P1/P2 = T1^4d1^2/T2^4d2^2

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16
Q

Order of spectral classes

A 
O: Oh
B: Bugger
A: A
F: Fucking
G: Goat
K: Killed
M: Me

Hottest temperature is for O (blue) and coolest is for M (red)

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17
Q

Balmer series

A

Excitation from n=2

Useful since visible light so can be detected

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18
Q

Spectral class O prominence of Balmer lines

A

Weak

Collisions of atoms at high energy levels ionise hydrogen

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19
Q

Spectral class B prominence of Balmer lines

A

Slightly stronger

Collisions of atoms at high energies ionise hydrogen

20
Q

Spectral class A prominence of Balmer lines

A

Strongest

Collisions cause excitation from n=2

21
Q

Spectral class F prominence of Balmer lines

A

Weak
Too cool, collisions not enough energy to cause excitation from n=2
From n=1 instead

22
Q

Spectral class G prominence of Balmer lines

A

Very weak

Collisions with not enough energy to separate H2 into H atoms and causes excitation from n=2

23
Q

Spectral class K prominence of Balmer lines

A

Very weak

Collisions with not enough energy to separate H2 into H atoms and causes excitation from n=2

24
Q

Spectral class M prominence of Balmer lines

A

Very weak

Collisions with not enough energy to separate H2 into H atoms and causes excitation from n=2

25
Q

Explain the Hertzsprung Russell diagram

A

Scatter graph
With stars as the point on the graph
y axis is absolute magnitude from +15 to -10
x axis can be spectral class or surface temperature

26
Q

For the four bubbles on the H-R diagram

A

Top horizontal = red super giants
Next slanty bubble = red giants
Funky squiggle bubble = main sequence
Bottom = white dwarf

27
Q

What does Stefan’s law tell us

A

That hot stars should be relatively bright

Cools stars relatively dim

28
Q

What does Hertzsprung Russel diagram tell us about white dwarfs

A

Very dim but very hot

Although T is very high, a really low surface area means a lower lower and hence brightness

29
Q

Exoplanet/Extra-solar planet

A

Any planet not in our solar system
Hard to detect don’t emit light

satellite of any star other than the sun

30
Q

Why are exoplanets hard to find

A

Orbiting stars much brighter than them
Can’t be seen directly because they mostly only reflect light and are too dim to be seen from Earth

Subtend too small of an angle with their star for resolution in a telescope
Only a few of the largest hottest and nearest exoplanets that are furthest away from their star can be seen directly using specially built telescopes

31
Q

Two methods to find exoplanets

A

Doppler shift/radial velocity method

Transit method

32
Q

Explain the Doppler shift for exoplanets

A

Measures how much lines from a star has been red and blue shifted from its mean value over a period of time
Due to the star rotating about the centre of mass of the star planet system and wobbles towards us in part of the orbit giving a relative blue shift and away giving a relative red shift

Changes are small since stars have a high mass relative to planet
This method can be used to get the mass of the planet
Stars movement and plane of orbit must be in line with the observers line of sight

33
Q

Quasar

A

Galaxy
Particularly large concentration of gas, dust and matter near to the black hole at its centre is draw in and its gravitational potential energy decreases, kinetic and thermal increase
So high energy radiation emit above and below accretion disc due to the black hole and the thermal energy

34
Q

Which galaxies are believed to have a black hole at the centre

A

All

35
Q

Why are Quasars hard to detect/condition to detect quasar

A

Have to be in line with the jets of high energy radiation (directly above or below)

We observe very large radio wave signals because the gamma wavelengths have been red shifted
So the quasar is moving away from us
Because it is massive (one end of spectrum to the other) they must be the most distant observable things moving very very quickly

36
Q

Explain the transit method for

A

Changes in apparent magnitude as an exoplanet travels in front of a star are observed when some of the light is blocked from Earth’s view
Leading to a dip in the apparent magnitude observed
So can find the radius
But the chance of the planets path being perfectly aligned so its crosses the line of sight between the star and the Earth is very low

37
Q

What radiation is emit/detected and why from a quasar

A

We observe very large radio wave signals because the gamma wavelengths have been red shifted
So the quasar is moving away from us
Because it is massive (one end of spectrum to the other) they must be the most distant observable things moving very very quickly

38
Q

What has the greatest redshift

A

Quasars
Make the graph curve upwards
Was unexpected, so suggests the universes expansion is accelerating

39
Q

The universe is expanding…

A

At a constant rate

40
Q

What provides evidence that the universe is expanding at an increasing rate

A

Quasars

41
Q

Why are Quasars different

A

Have dense mater and dust and gas round their centre

GPE into thermal means they emit jets of high energy radiation

42
Q

What happens when the hydrogen stars to run out in the core of the sun

A 
Hydrogen is used up
Decreases radiation pressure
Core contracts rapidly
Big increase in temperature
Enough so helium can start fusing
Expansion of the outer layers which cool
43
Q

What elements may be produced by fusion reactions in the sun

A

Helium forms beryllium
Increase in temperature for carbon to form
Increase in pressure further for oxygen to form
Gravitational collapse raises temperature

44
Q

What is a planetary nebula

A

Final fusion processes stops due to lack of fuel
Core shrinks to raise temperature and outer layers blown off to lose about 50% of mass
Remainder shrinks to a high density

45
Q

Lifecycle of a star

A

Stellar nebula
Average size star = red giant = planetary nebula = white dwarf
Massive star = red super giant = supernova = Neutron star OR if massive a black hole

46
Q

Explain the universe creation

A

From gluons pairs of antiquarks and quarks were formed which annihilated and gave off more gluons
Somewhere along this time matter won over antimatter and 1 billion and 1 matter particles were made for 1 billion antiparticles
Universe expanded so leads to a decrease in temperature
Quarks form hadrons (p and n)
Temperature cools to be cold enough for neutrons to decay into protons and form hydrogen
Atoms form out of hadrons and electrons
Pressure increases so stars and galaxies can form and emit radiation

A Level Physics Paper 3 (10 decks)

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