Quantum and Astrophysics Flashcards

1
Q

Define electronvolt

A

One electronvolt is the energy gained by a single electron travelling through a potential difference of 1 volt

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2
Q

Define a photon

A

A photon is a quantum of energy of electromagnetic radiation.

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3
Q

What are features of a photon?

A

Zero rest mass
Zero charge
Travel at the speed of light in a vacuum
Not affected by electric or magnetic fields

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4
Q

What is the word equation for the photoelectric effect?

A

Energy of a single photon (hf) = minimum energy to escape (φ) + maximum kinetic energy of emitted electron (KEmax)

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5
Q

Define work function (φ)

A

The minimum energy required to remove an electron from the surface of a metal plate.

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6
Q

Define threshold frequency

A

The minimum frequency of electromagnetic radiation that will remove electrons from the surface of a metal plate.

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7
Q

How is energy carried by a ray of light?

A

By a stream of photons each with energy E=hf

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8
Q

When is a star on the main sequence?

A

When it is fusing hydrogen nuclei into helium nuclei.

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9
Q

Explain the relationship between time on the main sequence and mass of a star

A

A high mass star provides higher gravitational forces, the core is hotter and hydrogen is used up faster. A high mass star spends less time on the main sequence.

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10
Q

What will the sun evolve into?

A

From a main sequence star to a red giant to a white dwarf. It will spend a long time on the main sequence as it is a low mass star.

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11
Q

List the sun, a white dwarf and a red giant from most to least dense

A

White dwarf, sun, red giant

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12
Q

List the sun, a white dwarf and a red giant from having the most to least luminosity (power)

A

Red giant, sun, white dwarf

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13
Q

List the sun, a white dwarf and a red giant from the most to least intense surface (temperature at the surface)

A

White dwarf, sun, red giant

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14
Q

What is a black-body spectrum?

A

An object with a surface temperature above absolute zero, emits electromagnetic radiation. Its spectrum contains a range of wavelengths and intensities.

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15
Q

Define black-body for a star

A

A star absorbs all incident electromagnetic radiation and emits its own spectrum depending on its surface temperature.

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16
Q

Define luminosity

A

The total energy emitted per unit time.

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17
Q

What is one astronomical unit equal to?

A

1AU = 1.50x10^11m

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18
Q

How do electrons move between energy levels?

A

By gaining or emitting a fixed amount of energy.

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19
Q

Define ionisation energy

A

The amount of energy required to completely remove an electron from an atom.

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20
Q

Define excitation

A

When an electron moves from a lower to higher energy level. It receives the exact right amount of energy by absorbing a photon.

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21
Q

Define relaxation

A

An electron in an excited state will soon return to lower energy levels by emitting a photon so it loses energy.

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22
Q

Define continuous spectra

A

A continuous spectra contains all colours, wavelengths and frequencies.

23
Q

How is a continuous spectra made?

A

By viewing a white light source through a diffraction grating.

24
Q

Define an emission line spectrum

A

A series of narrow, bright, coloured lines on a dark background.

25
Q

How is an emission line spectrum made?

A

Each line in the spectrum is due to photon emission as electrons move to lower energy levels. The gaps between the energy levels are fixed so the photons have fixed energy, frequency and wavelength.

26
Q

Define an absorption line spectrum

A

A series of narrow dark lines on a continuous spectrum background.

27
Q

Why does each element have its own unique line spectrum?

A

Each element has its own unique line spectrum due to a unique set of energy levels.

28
Q

How is an absorption line spectrum made?

A

A continuous spectrum from a star passes through a cool gas. The gas absorbs certain photon energies producing excitation of electrons. Each photon energy absorbed corresponds to a gap between energy levels, so the element in the gas can be identified.

29
Q

Define the Doppler Effect

A

The observed change in wavelength due to relative motion between a source and observer.

30
Q

State Hubble’s Law

A

The speed of recession of distant galaxies is directly proportional to their distance away.

31
Q

What is a feature of cosmic microwave background radiation?

A

It is virtually uniform in all directions.

32
Q

Define CMBR

A

Photons from the Big Bang, originally gamma photons, with their wavelengths stretched due to expansion and energy reduced due to cooling.

33
Q

Define the Cosmological Principle

A

On a large scale, the universe is homogenous and isotopic with the universal laws of physics.

34
Q

Define homogenous

A

The universe has uniform density on the large scale.

35
Q

Define isotopic

A

The universe looks the same in all directions on a large scale.

36
Q

What is the equation for current due to the photoelectric effect?

A

I = number of photons emitted per second x e

37
Q

Define stellar parallax

A

The apparent movement of a star due to movement of the observer’s position.

38
Q

Define a parsec

A

A star at a distance one parsec produces a parallax angle of 1 arc-second in a triangle of base one astronomical unit.

39
Q

Define red shift

A

Distant galaxies have the same spectrum but each line is shifted to longer wavelengths at the red end of the spectrum. (Distant galaxy is moving away from the observer)

40
Q

Why does the KE of emitted electrons range from 0 to max?

A

Free electrons lose kinetic energy due to collisions as they escape from the metal.

41
Q

When does a main sequence star evolve?

A

When hydrogen in the core runs out.

42
Q

What is electron degeneracy pressure in a white dwarf?

A

A quantum effect preventing all electrons in the core from occupying the lowest energy levels at once.

43
Q

What is the Chandrasekhar limit?

A

A white dwarf has a maximum mass of 1.44 solar masses

44
Q

How is stability maintained by a white dwarf?

A

By electron degeneracy pressure.

45
Q

What is 1 arc-second equal to?

A

1/3600 of a degree

46
Q

What is the ground state energy level?

47
Q

If n=3.99 what is nmax?

48
Q

What do the letters in the equation dsinθ = nλ represent?

A

d - slit separation
n - maximum order number
λ - wavelength of monochromatic light

49
Q

What is the difference between red shift and blue shift?

A

Red shift - wavelength become stretched as the source is moving away from the observer.
Blue shift - wavelengths become compressed as the source is moving towards the observer.

50
Q

Δ λ/λ = Δf/f = v/c what is λ?

A

λ - the actual wavelength of the spectral line in a laboratory

51
Q

What is the composition of the universe?

A

70% dark energy
25% dark matter
5% ordinary matter

52
Q

What is 1 solar mass equal to?

A

1.99x10^30 kg

53
Q

When can stars evolve into supergiants?

A

If their mass is greater than 8 solar masses.

54
Q

What is an equation for intensity of electromagnetic radiation of incident light on a metal plate?

A

I = (hf x N) / A
N - number of photons per second