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A Level Physics > 10 - space > Flashcards

10 - space Flashcards

1
Q

What is the Astronomical Unit?

A

The astronomical unit is the mean distance between the Earth and the Sun.
1AU = 1.5 x 10^11m

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2
Q

What is the unit of a light year a measure of?

A

distance

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3
Q

What is a light year?

A

The distance through space that a light photon travels in the space of a year.
1ly = 9.46 x 10^15 m

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4
Q

What can parallax be used for?

A

Parallax can be used to calculate distances in space, using observations and trigonometry.

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5
Q

What is a parsec?

A

A parsec is an astronomical unit of distance. A star is one parsec (pc) away from the Earth if the parallax angle is 1 arcsecond.

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6
Q

What is a Hertzsprung-Russell diagram?

A

A Hertzsprung-Russell diagram is a plot of a star’s stellar luminosity against its surface temperature.

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7
Q

What category of star is represented by the main diagonal on a H-R diagram?

A

The main sequence stars.

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8
Q

What category of stars lie below the main sequence diagonal on a H-R diagram?

A

white dwarfs

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9
Q

What categories of stars lie above the main sequence diagonal on a H-R diagram?

A

red giants and red supergiants

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10
Q

State the equation linking the intensity, luminosity and distance of a star.

A

i = L / 4πd^2

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11
Q

What is the doppler effect?

A

The doppler effect is the apparent change of wavelength as result of relative movement between a receiver and source.

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12
Q

What happens to the observed wavelength of a wave source moving away from the observer?

A

The observed wavelength will increase.

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13
Q

What happens to the observed wavelength of a wave source moving towards an observer?

A

The observed wavelength will decrease.

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14
Q

What happens to the observed frequency of a wave source moving towards an observer?

A

the observed frequency will increase

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15
Q

What is red-shift?

A

Red-shift is the apparent shift of the wavelength of light emitted by a star towards the red end of the light spectrum, as a result of it receding.

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16
Q

What equations are used to calculate red-shift?

A

z = Δλ / λ = Δf / f = v / c

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17
Q

Describe how the relative speed value inputted into the equation differs depending on whether the source and receiver are nearing or receding.

A

If the source and receiver are approaching each other, the value should be negative, otherwise the value is positive.

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18
Q

What is the difference between a positive and negative ‘Z’ value?

A

A positive ‘z’ value represents red shift, whereas a negative value represents blue shift.

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19
Q

What are the two main conclusions that can be drawn from observations of red shift from distant galaxies?

A
  1. All galaxies show red shift and so all galaxies are moving away
  2. The more distant a galaxy is, the greater its red shift and so the faster it is receding
20
Q

What does the red-shift of distant galaxies provide evidence for?

A

Red-shift of distant galaxies suggests that they are moving away from us. This supports
the concept that the universe is expanding, which supports the Big Bang theory.

21
Q

What does CMBR stand for?

A

Cosmic Microwave Background
Radiation

22
Q

What is cosmic microwave background radiation?

A

Radiation in the microwave region of the
EM spectrum that is present in very small quantities all around us.

23
Q

How does the existence of CMBR support the Big Bang theory?

A

In the big bang, lots of high energy radiation was produced. As the universe has expanded over time, the wavelength of this radiation has been ‘stretched’ so that it is now in the microwave region. Other theories of the universe can’t account for the existence of CMBR.

24
Q

What is the Big Bang theory?

A

The Big Bang theory is a theory for the formation of the universe. It proposes that the universe began from a very small, hot and dense region, and expanded from this point.

25
What two quantities does Hubble's law relate?
The distance of a galaxy to the speed at which it is moving away.
26
Express Hubble's law in words.
The speed at which a galaxy is moving away, is directly proportional to the distance it is at.
27
State the defining equation for Hubble's law.
V = Hod Where Ho is Hubble's Constant
28
Describe what was observed when observations of galaxies' brightnesses were compared to the predictions made by Hubble's Law.
• The actual and predicted brightnesses of distant galaxies don't always agree with each other • Distant galaxies aren't as bright as predicted by Hubble's Law, suggesting that they are more distant than predicted
29
State the conclusion that can be made from Hubble's Law and observations.
The rate of expansion of the universe is accelerating, since galaxies are further away than predicted.
30
Give one possible explanation for the acceleration of the universe's expansion.
The existence of dark energy. This would explain where the energy required for the expansion rate to constantly accelerate comes from.
31
Why is the existence of dark energy still only a hypothesis?
Dark matter and energy can't easily be observed.
32
how much is one arc second worth
1/3600 of a degree
33
what does luminosity depend on
temperature, size / surface area
34
what is the cepheid variable
stars which brighten and dim periodically. we can get a stars luminosity without knowing the distance, but how fast thet flash (brightness changes). the luminoity increases as the period of flashing increases
35
explain the uV catastrophe
as intensity increases frequency increases due to E = hf, to infinity. as f is much higer you would expect higher frequency radiation emited. but instead its mainly uv. this is due to far fewer high energy transitions, so doesnt really happen. so we dont get gamma radiation (highest freuquency radiation)
36
desciribe life cycle of a star
1) Within a stellar nebula, clouds of dust, hydrogen and helium stick together. When they stick together under gravity, the clumps rotate and the conservation of momentum spins them inwards to form a denser centre of gas – a protostar 2) It then forms into a main sequence star, it can turn into either a smaller star (like the sun) or a larger star. 3) The inward force of gravity and the force due to fusion, makes the star in hydrostatic equilibrium. Fusion is where hydrogen nuclei fuse into helium. The greater the mass of the star, the shorter its main sequence period as it uses more fuel more quickly. 4) Once hydrogen runs out, the temperature of the core increases and begins fusing helium nuclei into heavier elements. The outer layers expand and cool. A red supergiant can fuse elements nuclei up until iron. 5) Once the fuel is used up, fusion stops and the core contracts as the gravity is now greater than the fusion force so the star is no longer in hydrostatic equilibrium. The heat and pressure from the core ejects the outer layers of the star into space. A planetary nebula is formed, leaving lots of different elements. This leaves a white dwarf. 6) This white dwarf will eventually cool into a black dwarf. If it’s a larger mass star, when the red supergiant runs out of fuel, the core collapses in on itself as gravity becomes so great and is no longer in hydrostatic equilibrium The outer layers of the star fall inwards and rebound off of the core, launching them out into space in a shockwave. As the shockwave passes through surrounding material, elements heavier than iron are fused and flung out into space. The remaining core depends on the mass of the star. 7) When the core of the large star collapses, gravity is so strong that it forces protons and electrons together to form neutrons, causing a neutron star. 8) If the mass of the core is even larger, then a black hole will be formed as the neutrons are unable to withstand gravity forcing them together. Not even light can escape due to the gravitational pull.
37
what is the relationship between rate of fusion and the stars mass
as the mass of the star increases, temp in the core increases leading to increased pressure, allowng them to fuse heavier elements and use more fuel, thereofre increasing the rate of fusion
38
what is the relationship between the stability of the star and the size of the star
the smaller the maib sequence star, the less luminosity the star has, less energy so less mass is lost per second so the star is more stable the smaller it is
39
what is the relationship between mass and colour of a star
the more massive stars are, they will have a hotter core due to the increased rate of fusion leading to a shorter wavelength like blue
40
what does red shift tell us
red shift does not tell us how far away something is it just tells us how fast something is moving
41
what does the doppler effect show
shows how freuency and wavelength change for objects moving towards you or away from you. its the same thing with distant galaxies. it compares the wavelength of absorption lines from distant galaxies/stars and compares it with our sun’s
42
what is stellar spectroscopy
it uses absorption lines and can reveal many properties of stars such as their chemical composition, temperatire, desnity, mass, distance and luminosity. and can show the velocity of motion.
43
what is the future of our universe
the universe is expanding only force we know permeating whole universe is gravity which should slow expansion the rate of slowing is linked to the average density of matter in the universe dark energy is whats causing the universe to expand at a quicker rate dakr matter is missing mass in the universe
44
what is the value ofone parsec
1 parsec = 3.1 x 10^16
45
why are absorption lines created by the sun
absorption lines are produced from stars as specific wavelengths in the star get absorbed to excite the electrons. the inner layers of the star give off all the colours of the rainbow in different amounts. as the ligher passes through a hydrogen cloud in the outer kayers of the str, some red light is absorbed by the hydrogen
46
explain how stars core emits all colours
the core emits all colours of the rainbow as the core is so hot so energy levels get closer and closer together so emits all light is emitted as so many transitions

A Level Physics (11 decks)

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