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Higher Physics > Our Dynamic Universe > Flashcards

Our Dynamic Universe Flashcards

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1
Q

What is the Doppler effect?

A

the apparent change in wavelength (and therefore frequency) observed when a source of a wave is moving relative to a stationary observer.

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2
Q

If an emergency vehicle (such as an ambulance) passes a stationary observer, what happens to the frequency of the siren as it passes?

A

there is a notable change in frequency.

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3
Q

If both the vehicle and observer are stationary, what effect will this have on the frequency observed?

A

No effect

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4
Q

More sound waves are received by the observer per second when the source of sound is moving in what direction- and so what happens to the observed frequency (f0)?

A

source of sound is moving towards them, and so the observed frequency (f0) is increased

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5
Q

More sound waves are received by the observer per second when the source of sound is moving towards them, and so the observed frequency (f0) is increased.
Why does this happen?

A

This happens because each successive wave reaches the observer quicker than its predecessor as wave speed and relative motion combine…

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6
Q

A siren moving towards an observer -what happens to the size of the wavelength and frequency?

A

wavelength has been reduced and the frequency has increased.

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7
Q

As the source of sound moves away from the observer the number of waves received every second is what and as a result the observed frequency (f0) is what

A

reduced waves

frequency decreases

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8
Q

As the source of sound moves away from the observer the number of waves received every second is reduced and as a result the observed frequency (f0) decreases.
Why does this happen?

A

This happens because each successive wave reaches the observer more slowly than its predecessor as wave speed and relative motion combine.

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9
Q

What is the doppler equation?

A

f0 is the observed frequency
fs is the frequency emitted by the source
v is the speed of sound in air (340 ms-1)
vs is the speed of the source.

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10
Q

What is the speed of sound in the air?

A

340ms-1

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11
Q

If the source is moving TOWARDS the observer what sign do you use in the doppler equation?

A

NEGATIVE

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12
Q

.If the source is moving AWAY from the observer what sign do you use in the doppler equation?

A

POSITIVE

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13
Q

The Doppler effect can also be applied to what object (space)?

A

moving objects that emit light

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14
Q

Light from objects moving away from us is shifted to what wavelengths.

A

longer wavelengths

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15
Q

What is the definition of redshift?

A

Light from objects moving away from us is shifted to longer wavelengths.

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16
Q

How do you calculate the redshift of a galaxy?

A

To calculate the redshift of a galaxy, you divide the change in wavelength of light by the wavelength of light emitted by the galaxy.

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17
Q

Redshift takes what symbol and has no what?

A

Z and no units.

(𝜆_𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑−𝜆_𝑟𝑒𝑠𝑡) /𝜆_𝑟𝑒𝑠𝑡

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18
Q

slowly moving galaxies, redshift can be determined by the ratio of the velocity of the galaxy to the velocity of what?

A

Light

𝑧=𝑣/𝑐

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19
Q

When Hubble plotted the velocities of the galaxies against their distances away from us, he found what?

A

directly proportional to each other, with the constant of proportionality known as the Hubble constant, H0.

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20
Q

How do you calculate the velocity of galaxies?

A

𝑣=𝐻0 x𝑑

Where
v = velocity of distant galaxy (in ms-1)
H0 = The Hubble constant (2.3 × 10^(−18) 𝑠^(−1))
d = distance to galaxy (in m)

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21
Q

What does the Hubble Lemaitre law allow us to estimate?

A

age of the universe

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22
Q

What is dark energy?

A

name was given to the unknown force which causes the accelerating rate of expansion of the universe.

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23
Q

The mass of a galaxy can be estimated by what?

A

the orbital speed of stars within it.

24
Q

What is the evidence for the existence of dark matter?

A

estimating size of galaxies

25
Q

What is the evidence for the existence of dark energy?

A

accelerating expansion of the universe

26
Q

The temperature of stellar objects is related to what?

A

the distribution of emitted radiation over a wide range of wavelengths.

27
Q

The peak wavelength of the distribution of emitted radiation over a wide range of wavelengths is what for hotter objects than cooler objects?

A

Shorter

28
Q

Hotter stars also emit more what per unit area per unit time than cool ones, shown by the ‘higher’ peaks.

A

radiation per unit area per unit time

29
Q

It can be shown that the relationship between the peak wavelength and the surface temperature (in K) of a star is approximately what?

A

𝑇 × 𝜆𝑝𝑒𝑎𝑘=2.9 × 10^(−3)

30
Q

Describe the evidence for the big bang theory

A

The expanding universe- Large number of galaxies showing redshift (rather than blueshift)
The number of these showing redshift far outweighs the number showing blueshift, which supports the expanding universe from a single point (the ‘big bang’).

Cosmic microwave background radiation (CMBR)
At the start of the universe after the big bang, there was a huge single emission of energy.
It is the dominant source of radiation in the Universe.
It is very uniform (throughout the Universe).

The darkness of the sky (Olber’s paradox),
Some stars are moving with enough velocity that their visible light is redshifted into the infra-red, so we cannot see it.
We see CMBR in the regions of space where there is no visible light.

The abundance of the elements Hydrogen and Helium in the universe
About 98% of all matter in the universe is still H or He, which is consistent with the big bang model of the universe.

31
Q

Any two things moving at the same velocity (speed and direction) together are in the same what?

A

‘reference frame’.

32
Q

If something is moving relative to you, it is in another what?

A

reference frame.

33
Q

What are Einstein’s two “ Postulates” of special relativity?

A

When two observers are moving at constant velocities relative to one another, they will observe the same laws of physics.

The speed of light (in a vacuum) is the same for all observers in all reference frames.

34
Q

What is time dilation?

A

Time dilation is a difference in a time interval as measured by a ‘stationary’ observer and a moving observer.

35
Q

Describe the time dilation equation

A

𝑡^′=𝑡/√(1−𝑣^2/𝑐^2 )
Where

t’ = dilated time, t = proper time, v = speed of relative motion between two reference frames, c = the speed of light.

36
Q

What is t’ (t prime)?

A

t’ is the time measurement made by an observer in a different frame of reference to the event.
(t’ is pronounced “t prime”.)

Try not to get too stuck on which observer is the ‘stationary’ one- because they are both stationary within their own reference frames!

37
Q

What is length contraction?

A

Length contraction is a difference in length as measured by a ‘stationary’ observer and a moving observer.

38
Q

Describe the length contraction equation?

A

𝑙′=𝑙√(1−𝑣^2/𝑐^2 )

Where l’= contracted length, l = proper length, v = speed of relative motion between two reference frames, c = the speed of light

39
Q

Describe the sign convention for equations of motion

A

Left- negative
Right-postive
UP- positive
Down-negative

40
Q

Describe the equations of motion?

A

Equation 1: 𝒗=𝒖+𝒂𝒕

Equation 2: 𝒔=𝒖𝒕+𝟏/𝟐 𝒂𝒕^𝟐

Equation 3: 𝒗^𝟐=𝒖^𝟐+𝟐𝒂𝒔

41
Q

What number do we use as acceleration due to gravity in the calculation

A

-9.8ms-2

42
Q

An object thrown upwards with initial speed will have the same what but in the opposite sign

A

same speed

43
Q

What will be a object’s speed at its maximum height?

A

Oms-1

44
Q

An object takes the same amount of time to reach its maximum height as it does to do to do what?

A

fall back down to where it started.

45
Q

When an object is thrown upwards and falls back down to where it started, its overall displacement is what?

A

0m.

46
Q

What does the constant velocity displacement against the time graph look like?

A

The directly proportional line going up the way

47
Q

What does the constant velocity velocity against the time graph look like?

A

Horizontal straight line up above 0

48
Q

What does the constant velocity acceleration against the time graph look like?

A

Horizontal straight line up ON 0

49
Q

What does the constant positive acceleration displacement against the time graph look like?

A

Curved line up the way (levels of bottom)

50
Q

What does the constant positive acceleration velocity against the time graph look like?

A

straight line up the way directly proportional

51
Q

What does the constant positive acceleration acceleration against the time graph look like?

A

straight line horizontal above 0

52
Q

What does the constant negative acceleration displacement against the time graph look like?

A

curved line up the way (levels of at top)

53
Q

What does the constant negative acceleration velocity against the time graph look like?

A

the negative line going down diagonal

54
Q

What does the constant negative acceleration acceleration against the time graph look like?

A

Below 0 line horizontal

55
Q

Whenever a velocity-time graph crosses the x-axis this indicates what?

A

change of direction

56
Q

The gradient of the velocity-time graph gives the constant value of what?

A

acceleration

Higher Physics (1 decks)

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