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Physics Paper 3 > Astro > Flashcards

Astro Flashcards

1
Q

When is the Doppler effect observed?

A

when there is relative motion between two objects that are in a wave pair. there is an emitter and a receiver. eg. a car passing a person stood still.

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2
Q

What happens when an object moves further away from the other in Doppler effect?

A

wavelength gets longer
frequency decreases
light would get redder
sound would get lower

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3
Q

What happens when an object moves closer to the other object in Doppler effect?

A

wavelength gets shorter
frequency increases
light would get bluer
sound would get higher

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4
Q

When is required for Doppler shift to occur?

A

v is much greater than c. (non-relativistic)

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5
Q

What is meant by a ‘nearby’ galaxy?

A

it is not receding significantly by universala expansion. ie. ignore redshift of galaxy as a whole away from us

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6
Q

Why does the Doppler effect on a rotational galaxy increase the further from the centre?

A

If a galaxy spins with constant angular velocity, ω, then velocity, v, will increase the further from the centre, causing a greater doppler effect.
v = ωr

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7
Q

Why is Doppler shift harder to measure on galaxies than planets?

A

Galaxies are more complex as they are not solid so don’t spin with constant angular velocity, like planets do

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8
Q

What is Hubble’s law?

A

v ∝ r so v=Hd

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9
Q

What evidence is there to support Hubble’s law?

A

light from all galaxies is red shifted so they must be moving away from us with recessional velocity, v.
the further away a galaxy is, d in megaparsecs, the greater the recessional velocity

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10
Q

What is the current value of Hubble’s constant?

A

65km/s/MPc

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11
Q

Describe the universe at t=0.

A

a singularity
infinitely hot and dense
four fundamental forces combined into a super force

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12
Q

How and when did matter and antimatter form in the timeline of the universe?

A

t = 1x10^-27s
ratio of matter to antimatter is M : AM, 10^9 +1 : 10^9
so majority annihilates leaving a small amount of matter which goes on to create everything

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13
Q

When did quarks form?

A

t = 1x10^-12s to 1x10^-6s

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14
Q

When did hadrons form?

A

t = 1x10^-6s - 1s

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15
Q

What happened between the times of 1s and 20mins in the timeline of the universe?

A

Nucleosynthesis

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16
Q

What was the ratio of elements in the universe before stars as seen today?

A

H : He : Li

75 : 24 : 1

17
Q

What are the advantages of refracting telescopes?

A

robust
sealed - low maintenance
air doesn’t circulate so sharper image

18
Q

What are the disadvantages of refracting telescopes?

A

chromatic aberration
not all wavelengths of EM spectrum pass through glass
larger lenses sag under their own weight

19
Q

What are the advantages of reflecting telescopes?

A

no chromatic aberration
long focal length for size so high magnification
less sag in both body and mirror

20
Q

What are the disadvantages of reflecting telescopes?

A

Open so air circulates causing turbulence (twinkles)
diffraction as light passes secondary reflectors
spherical aberration unless mirror is parabolic

21
Q

What is collecting power proportional to?

A

the area (and so diameter) of the lens

22
Q

What are the features of the objective lens in a refracting telescope?

A

convex
large diameter
long focal length

23
Q

What are the features of the eyepiece lens in a refracting telescope?

A

convex
smaller diameter
short focal length

24
Q

What type of mirrors are used in a Newtonian reflector?

A

convex and flat

25
Q

What type of mirrors are used in a Cassegrain telescope?

A

convex and concave

26
Q

What is resolving power?

A

the smallest angle of separation at which two points can be distinguished

27
Q

What is an airy disc?

A

when EM waves diffract through a circular gap or aperture they produce rings rather than fringes. This circular diffraction pattern is known as an airy disc.

28
Q

What is the Rayleigh criterion?

A

when the 1st minimum of object A falls under the maximum of object B, the two objects are just resolvable.
𝜃 = 𝜆 / D

Physics Paper 3 (1 decks)

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