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Higher Physics > Unit 1 - Our Dynamic Universe - Part 2 > Flashcards

Unit 1 - Our Dynamic Universe - Part 2 Flashcards

1
Q

why on earth do objects travel downwards with an acceleration of 9.8ms-2

A

gravitational field strength on earth

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2
Q

in newtons universal law of gravitation what is G

A

gravitational constant (6.67x1011m3kg-1g-2) - in data booklet dont worry :)

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3
Q

define a uniform field

A

constant in both strength and direction

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4
Q

how do satellites stay in orbit?

A

the gravitational field keeps them accelerating towards earth and the earth’s surface falls away at the same rate

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5
Q

what are some examples of natural satellites?

A

moon in orbiting earth and the planets in orbit around the Sun

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6
Q

why does it not matter that charged particles and atoms experience a gravitational force?

A

it is insignificant as the electrical and nuclear forces are much stronger

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7
Q

state Einstein’s postulates

A

The speed of light in a vacuum is a constant (3x10^8ms^-1) for all observers, regardless of their speed
The laws of physics are the same for all observers that travel at constant speed, within their own frame of reference

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8
Q

what are the effects of special relativity?

A

Length contraction - disagreeing about the lengths of objects when they are moving relative to an observer
Time dilation - disagreeing on the passage of time when a clock is moving relative to an observer

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9
Q

in the time dilation formula, what is the difference between t and t dash?

A

t is measured from perspective inside the frame of reference (astronaut on ship)
t dash is from observer outside the frame of reference (person on earth)
t dash = longer time
t= shorter time

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10
Q

with length contraction what direction does the object contract?

A

the lengths of objects decreases in the direction of its motion from the point of view of the stationary observer

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11
Q

in the length contraction formula, what is the difference between l and l dash?

A

l is measured from perspective inside the frame of reference (astronaut on ship)
l dash is from observer outside the frame of reference (person on earth)

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12
Q

for a stationary source of noise what happens to wavelength and frequency?

A

same in all directions, waves form concentric circles

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13
Q

if there is a source of noise moving towards you, what happens to wavelength and frequency?

A

the wave fronts are compressed, smaller wavelength higher frequency - therefore higher pitch sound

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14
Q

if there is a source of noise moving away from you, what happens to wavelength and frequency?

A

the wave fronts are stretched, bigger wavelength lower frequency - therefore lower pitch sound

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15
Q

what is fo?

A

frequency observed by the onlooker (Hz)

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16
Q

what is fs?

A

frequency of the source (Hz)

17
Q

what is vs?

A

speed of the source (ms-1)

18
Q

for doppler effect equation when do you + and when do you use -?

A

+ when source is moving away, - when source is moving towards

19
Q

what happens to objects that move away from us

A

emit light - wave fronts more stretched out, larger wavelength and lower frequency. Light is therefore shifted towards the red end of the spectrum - redshift

20
Q

what happens to objects that move towards us

A

emit light - wave front less stretched out - smaller wavelength and larger frequency. Light shifted towards the blue part of the spectrum - blue shift

21
Q

define redshift

A

a measure of the ratio of the change of wavelength against the original wavelength or as the ratio of velocity of the receding object and the speed of light

22
Q

what did Hubble’s studies find out?

A

Hubble’s studies found that most galaxies are receding from us and the recessional velocity increases with distance. There was a near proportional relationship between these two: v ∝ d

23
Q

what is Ho in Hubble’s law?

A

Hubble’s constant 2.34x10-18s-1 in data booklet dont worry :)

24
Q

what is the estimated age of the universe?

A

13.8 billion years

25
Q

what is the four pieces of evidence that support the big bang?

A

Cosmic microwave background radiation
Majority redshift if distant galaxies
Abundance of hydrogen and helium
Olbers’ Paradox

26
Q

what is meant by abundance of hydrogen and helium?

A

the abundance of hydrogen and helium present in the universe today matches those predicted by the big bang model - heavier elements would not survive such an event and can only be produced later through fusion in stars and eventually in supernovae for the heaviest elements.

27
Q

what is meant by Olbers’ Paradox?

A

if the universe was static and infinite in size and age then in every direction we look, we would eventually see the surface of a star and the sky would be constantly aglow. This is not true as stars move away from us and have not had enough time for their light to reach us yet. This tells us that the universe has a finite age (13.8 billion years) and is expanding.

28
Q

what is meant by Majority redshift if distant galaxies?

A

almost all galaxies are redshifted and therefore are moving away from us. In fact almost all other galaxies are moving away from each other telling us that the universe is expanding and this expansions origin is the Big Bang

29
Q

what is meant by Cosmic microwave background radiation?

A

shortly after the big bang as the universe cooled enough for electrons to recombine with hydrogen and helium atoms this recombination resulted in the release of light from all of these atoms, everywhere, all at once and in every direction. This light has been stretched out with the expansion of the Universe into the microwave part of the spectrum and can still be detected in every direction today.

30
Q

how can we estimate the mass of a galaxy?

A

by the orbital speed of stars within it - greater gravitational force causes larger accelerations

31
Q

what is dark matter?

A

the stars in most galaxies move faster than predicted, something must be adding to the gravitational force that we cannot detect

32
Q

what is dark energy?

A

All of our observations suggest that the expansion of the universe is accelerating. However if gravity is an attractive force this expansion should be slowing and will eventually cause the universe to collapse again. This expansion must there fore be driven by some unseen and undetectable force

33
Q

JUST LEARN THIS:

dont really understand, cant turn into questions :)

A

Temperature of Stellar objects is related to the distribution of emitted radiation over a wide range of wavelengths
Hotter stars are bluer as there is more light at shorter wavelengths - high peak and larger area of graph
Cooler stars are redder as there is more light at longer wavelengths - low peak and small area of graph

Higher Physics (5 decks)

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