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Physics A2 > CH 12 > Flashcards

CH 12 Flashcards

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1
Q

what are the planets in order?

A

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

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2
Q

What shape are the planets’ orbits?

A

nearly circular

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3
Q

what do planets, moons and comets do to light?

A

they REFLECT it

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4
Q

what are the orbits of comets?

A

highly elliptical

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5
Q

what are comets?

A

lumps of rock, ice and dust: “dirty snowballs”

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6
Q

how much further away does a comet orbit the sun and pluto does?

A

1000 times further

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7
Q

what’s the most famous comet and what time period does it orbit in?

A

Halley’s comet, which orbits in 76 years

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8
Q

How do you use radar?

A

A short pulse of radio waves is sent from a radio telescope towards a distant object.
When the pulse hits the surface of the object, it’s reflected back to Earth.
The telescope picks up the reflected radio waves and records the time, t , taken for them to return.

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9
Q

What is the equation for the distances between objects in the solar system

A

2d= ct

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10
Q

how do you use the radar method to find the average speed of an object relative to Earth?

A

you send two pulses separated by a certain time interval, to give two separate measurements of the object’s distance. The differences between the distances shows how far the object has moved in the time interval- and distance/ time= speed

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11
Q

what is the radar method based on?

A

1- the speed of the radio waves is the same on the way to the object and the way back to the telescope
2- the time taken for the radio waves to reach the object is the same as the time taken to return.

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12
Q

why must the object’s speed be much less than the speed of light?

A

so that there are no relativistic effects

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13
Q

what is a more accurate measurement of the speed of distant objects?

A

using Doppler shifts

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14
Q

what does the brightness of a star depend on?

A

its luminosity and its distance from us

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15
Q

what is apparent magnitude?

A

how bright a star looks when seen from Earth

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16
Q

what does apparent magnitude depend on?

A

depends on the stars absolute magniture

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17
Q

how do u find the distance to a star?

A

measure how bright is looks(apparent magnitude) and calculate how bright it really is (absolute magnitude)

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18
Q

what are standard candles?

A

where you ca calculate the brightness of directly

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19
Q

what’s an example of standard candles?

A

Cepheid variable stars because their brightness changes in a certain pattern

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20
Q

how are distances in the solar system often measure in?

A

Astronomical Units (AU)

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21
Q

define one AU

A

one AU is defined as the mean difference between Earth and the Sun

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22
Q

How was the size of the AU accurately known and when?

A

1769 when it was carefully measured during a transit of Venus

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23
Q

define a light year (ly)

A

the distance that electromagnetic waves travel through a vacuum in one year

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24
Q

1 ly is equivalent to how many AU?

A

63 000 AU

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25
Q

Au in m

A

1.50 x 10^11 m

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26
Q

ly in m

A

9.46 x 10^15

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27
Q

distance of sun to nearest star?

A

4.2 ly

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28
Q

milkyway galaxy distance in ly

A

100 000 ly

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29
Q

the observable universe distance

A

14 billion ly- its size is the age of the Universe multiplied by the speed of light

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30
Q

explain the doppler effect with a car

A

if the car is moving away from you the pitch will be lower and if it is moving towards you the pitch will be higher. Because when the car is moving away from you, the sound waves travel in the opposite direction from the car, so are stretched out- have longer wavelength and lower f

31
Q

how much the sound waves change depends on..

A

how fast the car is travelling- the greater its speed the larger the change

32
Q

what can the doppler effect be used for?

A

used to measure the speed of moving objects

33
Q

give examples of applications of the doppler effect

A

police radar guns measure the speed of cars using microwaves.
cosmologists measure the speed of distant stars using the light they emit

34
Q

what does the doppler effect mean

A

it means radiation emitted by distant objects is ‘shifted’

35
Q

how can u calculate the speed of distant objects relative to earth- give an example

A

by measuring how their movement affects the radiation they emit
eg. if u detect the radiation emitted by a hydrogen atom in a star and compare it with the radiation emitted by a hydrogen atom on earth, u can calculate how much radiation is ‘shifted’ and so determine the velocity of the star relative to the earth using the equation v/c= change in wavelength/ wavelength if v

36
Q

how the radiation is shifted depends on what

A

the movement of the object

37
Q

what is redshift

A

when an object is moving away from earth, the wavelengths of its radiation get longer and the frequencies get lower- it shifts towards the red end of the spectrum

38
Q

what is blueshift

A

when an object is moving towards earth, the wavelengths of its radiation get smaller and the frequencies get higher- it shifts towards the blue end of the spectrum

39
Q

what is the equation for finding the velocity of an object from the radiation it emits and absorbs?

A

v/c= change in wavelength/wavelength if v

40
Q

what do stars produce?

A

absorption spectra

41
Q

where is radiation emitted from in a star?

A

from a very hot region called the photosphere in a continuous spectrum

42
Q

what do atoms in the atmosphere of the star absorb?

A

certain wavelengths of the radiation, producing dark absorption lines within spectrum.
different atoms absorb different parts of the spectrum, resulting in a characteristic pattern for each atom.

43
Q

how can the composition of the stellar atmosphere be worked out?

A

by looking at the absorption lines from a star

44
Q

how can you use the stellar spectrum to show it has been shifted by the movement of the star?

A

once you have worked out which atoms make up the pattern of absorption lines, you can compare the position of the absorption lines for each atom in the star’s spectrum with the same spectrum recorded in the lab. this shows how much the spectrum has been shifted by the movement of the star.

45
Q

when does time dilation happen?

A

close to the speed of light

46
Q

time runs at different speeds..

A

for two objects moving relative to each other- but it’s only really noticeable close to the speed of light. this is called relativistic time dilaton

47
Q

look at equation in book pg 33

A

..

48
Q

what did Hubble realise?

A

that Recessional Velocity is proportional to distance

49
Q

what do spectra from galaxies all show?

A

redshift

50
Q

what does the amount of redshift give?

A

the recessional velocity- how fast the galaxy is moving away from Earth

51
Q

what is hubble’s law?

A

v= Hod where v= recessional velocity in kms^-1
d= distance in Mpc
Ho= Hubble’s constant in kms^-1Mpc^-1

52
Q

1 Mpc=

A

3.09 x 10^22 m

53
Q

Ho lies somewhere between?

A

50kms^-1Mpc^-1 and 100kms^-1Mpc^-1

54
Q

what is the SI unit for Ho?

A

s^-1

55
Q

how do you get Ho in SI units?

A

you need v in ms^-1 and d in m

56
Q

why is Hubble’s work strong evidence that the Universe is expanding?

A

by showing that objects in the Universe are moving away from each other.

57
Q

what does the rate of expansion depend on?

A

the value of Hubble’s constant

58
Q

how do cosmologists tend to look at the expansion of the Universe?

A

that space itself is expanding and the light waves are being stretched along with it. This is called COSMOLOGICAL REDSHIFT.

59
Q

since the Universe is expanding uniformly away from us, what does this seem?

A

that we’re at the centre of the Universe but this is an illusion. You would observe the same thing at any point in the Universe.

60
Q

what do the age and observable size of the universe depend on

A

Ho

61
Q

what is the age of the universe if it has been expanding at the same rate for its whole life?

A

t=1/Ho (time = distance/ speed) only an estimate has probably hasn’t been expanding at the same rate

62
Q

if H0= 75 kms^-1Mpc^-1, what is the age of the universe?

A

roughly= 1/ (2.4 x 10^-18 s^-1) = 4.1 x 10^17 s, which is approx. 13 billion years

63
Q

what is the limit on the size of the observable Universe?

A

this is a sphere with the earth at its centre with a radius equal to the max distance that light can travel during its age so if Ho = 75kms^-1Mpc^-1 then the sphere will have a radius of 13 billion light years.

64
Q

the hot big bang (HBB):

A

the Universe started off very hot and very dense and has been expanding ever since.

65
Q

what does the HBB model predict?

A

That loads of electromagnetic radiation was produced in the very early Universe. This radiation should still be observed today.

66
Q

what has happened because the Universe has expanded? who picked this up?

A

the wavelengths of this cosmic background radiation have been stretched and are now in the microwave region.This was picked up accidentally by Penzias and Wilson in the 1960s.

67
Q

CMBR=

A

Cosmic microwave background radiation

68
Q

COBE satellite=

A

cosmic background explorer

69
Q

what did the COBE find in the late 1980s?

A

a continuous spectrum corresponding to a temperature of 2.73 K

70
Q

what was the radiation like that COBE found?

A

largely isotropic and homogeneous

71
Q

what was the temperature like that COBE found and what are they due to?

A

very tiny fluctuations in temperature, which were at the limit of COBE’s detection. these are due to tiny energy-density variations in the early Universe, and are needed for the initial ‘seeding’ of galaxy formation.

72
Q

what does the background radiation also show?

A

shows a Doppler shift, indicating the Earth’s motion through space. It turns out that the milky way is rushing towards an unknown mass (the Great Attractor) at over a million miles an hour.

73
Q

what can the HBB model explain about helium?

A

it explained the large abundance of helium in the Universe. The early Universe had been very hot for hydrogen fusion to happen. This means that, together with the theory of the synthesis of the heavier elements in stars, the relative abundances of all of the elements can be accounted for.

Physics A2 (1 decks)

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