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Theoretical physics year 1 > Phy104 > Flashcards

Phy104 Flashcards

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1
Q

Visible range of spectrum of light is between what values?

A

400 - 700nm

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2
Q

What is the equation for momentum of a photon?

A

rho=E/c

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3
Q

Qualitatively what is monochromatic flux?

A

Energy through a unit area per unit time at one frequency

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4
Q

What is the equation for monochromatic flux?

A

F_v=lim(deltaA->0, Deltaf->0, Deltat->0) DeltaE/(Deltat*DeltaA*Deltaf)

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5
Q

Qualitatively what is bolometric flux?

A

The energy through a unit area per unit time for all wavelengths

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6
Q

What is the equation for bolometric flux?

A

*add image*

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7
Q

What is the equation linking monochromatic flux in terms of frequency and mono flux in terms of wavelength?

A

*add image*

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8
Q

Qualitatively what is luminosity?

A

Total energy emitted by a source per unit time

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9
Q

Qualitatively what is monochromatic luminosity?

A

Energy output of an object per unit time per unit wavelength

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10
Q

Qualitatively what is bolometric luminosity?

A

The total energy emitted by a source per unit time at all wave lengths

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11
Q

What is the equation for inverse square law (Including bolometric luminosity and flux)?

A

*add image*

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12
Q

Derive the equation for inverse square law in terms of bolometric flux

A

*add image*

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13
Q

Derive the equation for relationship between magnitude and monochromatic flux

A

*add image*

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14
Q

Why is the value of c in the magnitude eqn chosen to be this specific value?

A

So that the star ‘vega’ has a magnitude of zero in every band

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15
Q

What are ‘Photometric systems’?

A

The sets of filters used to isolate individual wavelength ranges to measure monochromatic flux

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16
Q

What is the equation for energy collected by a camera with a ‘photometric system’?

A

*add image*

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17
Q

What is the equation for ‘colour indices’ to estimate temperature of stars

A

*add image*

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18
Q

Qualitatively what is ‘absolute magnitude’?

A

Magnitude an object would have if placed 10 parsecs away

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19
Q

What is the equation relating absolute and apparent magnitude? What is the unit for ‘d’?

A

*add image*

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20
Q

How do you combine magnitudes?

A

*find this out*

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21
Q

Qualitatively what is parallax?

A

The way an object appears to change position relative to it’s background when viewed down different lines of sight

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22
Q

What is a standard candle?

A

An object of accurately known luminosity

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23
Q

What is a cepheid variable?

A

A pulsating star whose brightness varies periodically

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24
Q

Accurately describe a type 1a supernovae

A

Explosions of white dwarfs in binary systems, the white dwarf accretes mass from it’s companion until it reaches 1.4 solar masses. It overcomes electron degeneracy pressure and collapses into a neutron star and sheds it’s outer layers in a supernovae 14 times brighter than the brightest cepheid variable

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25
Q

What is space velocity?

A

A stars velocity through space

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26
Q

Qualitatively what is radial velocity?

A

Velocity along our line of sight

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27
Q

Qualitatively define proper motion

A

The component of a stars space velocity in the plane of the nights sky

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28
Q

What effect can be used to measure radial velocity?

A

Doppler shift

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29
Q

What is the equation for doppler shift?

A

*add image*

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30
Q

Derive the equation for parsecs

A

*add image*

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31
Q

How is doppler shift used measured?

A

By comparing spectrum of object to the rest spectrum

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32
Q

Derive red shift with respect to wave length

A

*add image*

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33
Q

What is hubble’s law? What do it’s components mean?

A

*add image*

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34
Q

What are the assumptions for a black body?

A

.Body is in thermal equilibrium with surroundings .Body reflects no light

35
Q

What is the equation for black body radiation?

A

*add image*

36
Q

What is Wein’s law? What is the constants value?

A

*add image*

37
Q

Derive the stefan-boltzmann equation equation by integrating over all wave lengths

A

*add image*

38
Q

What is the equation for bolometric luminosity in terms of temperature T

A

*add image*

39
Q

What is synchrotron radiation?

A

.Fast spinning electrons near speed of light .strong field . Emitted as radio waves

40
Q

What is Bremsstrahlung radiation

A

.Emitted from ionised gas .Electrons decelerate as they move past protons . Decelerating electrons emit radiation . Mostly high frequencies

41
Q

What are optical, infrared, radio waves and x-rays each emitted from?

A

Optical - Hot objects (stars) Infrared - cooler objects (dust) Radio - synchrotron X-ray - Bremsstrahlung

42
Q

Conditions for a black body?

A

. Thermal equilibrium . Properties of matter described by statistical physics

43
Q

What is e equation for the most probable speed in a maxwell-boltzmann distribution?

A

*add image*

44
Q

What is the equation for the mean velocity of the maxwell boltzmann distribution?

A

*add image*

45
Q

Derive the ideal gas law

A

*add image*

45
Q

What is the equation for radiation pressure? (Photons exert pressure)

A

*add image*

46
Q

What general type of object gives a continuous spectrum?

A

Hot dense gas or hot solid

47
Q

What type of object gives an emission spectra?

A

Hot low density gas

48
Q

What type of object gives a continuous spectrum with absorption lines?

A

Continuous spectrum emitter viewed through a cool low density gas

49
Q

Draw diagram of line strength over spectral type

A

*add image*

50
Q

What is the equation for total energy of an electron orbiting in the Bohr atom?

A

*ad image*

51
Q

What is the equation of the radius of an electrons orbit?

A

*add image*

52
Q

What lines are the balmer emissions between?

A

Any line greater than n=2 and n=2, in a hydrogen atom

53
Q

What characteristics do O-class stars have?

A

.Blue in colour .strong HeII lines .HeI absorption lines

54
Q

What are characteristics for B-class stars?

A

.Blue white colour . HeII lines peak at B2 .HI balmer lines increasing in strength

55
Q

What are characteristics for A-class stars?

A

.White stars .Balmer lines strongest at A0 .CaII lines becoming stronger

56
Q

What are characteristics for F- class stars?

A

.Yellow/white stars .CaII lines strengthen as Balmer lines weaken .Neutral metal lines appear (FeI, CrI)

57
Q

What are characteristics for G-class stars?

A

.Yellow star .CaII lines continue to strengthen .Neutral metal lines stronger

58
Q

What are characteristics for K-class stars?

A

. Cool orange star .CaII lines peak at K0 . Neutral metal lines dominate

59
Q

What are characteristics for M-class stars?

A

. Cool red . Molecular absorption bands dominate (TiO & VO) . Strong neutral metal lines

60
Q

What is the boltzmann equation?

A

*add image*

61
Q

What is the Saha equation?

A

*add image*

62
Q

What is kepler’s 1st law?

A

The orbit of every planet is an ellipse with the sun at its focus

63
Q

What is keper’s second law?

A

As a planet orbits it’s radius vector sweeps out an equal area per unit time at all points in its orbit

64
Q

Qulaitatively what is kepler’s third law?

A

Cube of semi major axis is proportional to planetary period squared

65
Q

Derive kepler’s third law

A

*add image*

66
Q

What approximation is made when measuring relative masses of planets?

A

. Mass of moon is much less than the planet . Mass of planet is much less than mass of sun 1+(m_m/m_p) & 1+(m_p/m_s) ~ 1

67
Q

What is cavendish’s experiment?

A

. Torsion wire with small masses . Larger known masses . By cancelling two equations in terms of newton’s law you are left with an equation in terms of known masses and mass of the earth forces and radius of earth and between the small and large mass

68
Q

What is ‘seeing’?

A

Blurring and twinkling due to refractive index changes to the earths atmosphere due to turbulence

69
Q

What does ‘unresolved’ mean?

A

Seeing multiple objects as one blurred object

70
Q

What are visual binaries?

A

Binaries in which we can clearly see both stars

71
Q

How do you find the mass of stars in a binary system?

A

Replace M with (m1 + m2) in kepler’s third law, once the total mass is known and the ratio of the masses we can calculate the mass of each

72
Q

What is orbital inclination?

A

Angle between a reference plane and the orbital plane of an object

73
Q

What are stereoscopic binaries?

A

Binary star system that’s components cannot be resolved individually.

74
Q

What is a double lined spectroscopic binary?

A

When both binaries are comparably bright and absorption lines from both stars are able to be seen

75
Q

How can we measure stellar masses of double lined spectroscopic binaries?

A

Using radial velocity measurements and a rearrangement of kepler’s law

76
Q

What does a double lined binary tell us if it is eclipsing?

A

. Stellar masses . Stellar radii . Ratio of effective temperature

77
Q

What is a single lined binary?

A

A binary star in which one component is much brighter than the other so the spectrum of the fainter star is overwhelmed

78
Q

What are the methods of finding exoplanets?

A

Doppler wobble - Measuring radial velocity of star due to exoplanet Exoplanetary transit - causes a tiny dip in light as the exoplanet moves across the star

79
Q

What is the method for doppler wobble measurements?

A

. Absorption lines measured for host star . Spectrographs are built using iodine cells . Starlight shon through before experiment superimposes spectral lines for the experiment . Shift of spectral lines used to calculate velocity

80
Q

What is hyperfine splitting?

A

Electrons orbiting in one arm rotate at higher energy than electrons orbiting protons in the other, this gives a spectrum in radio frequency that can be used with radio spectroscopy for starless parts of a galaxy

81
Q

What do we see vs expect from a galaxy rotation curve?

A

Expectation: Rotational velocity increases linearly with radius Outside galaxy mass is constant so rotational velocity slowly drops off

82
Q

What is ‘virial theorem’?

A

Kinetic energy of a large self gravitating system (eg galaxy cluster) -1/2 it’s gravitational potential energy

Theoretical physics year 1 (3 decks)

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