Flashcards
Gravitational fields
Cards in this deck (80)
- 1What is Luminosity?•The rate at which energy
•of all types of electromagnetic radiation
•is emitted by an object
•in all directions - 2What is the unit of Luminosity?•Watt (W)
- 3What is the Stefan-Boltzmann law?Luminosity is directly proportional to the:
•surface area
•4th power of the absolute temperature of the surface. - 4What is Wien's law?•Wavelength at the maximum intensity is inversely proportional to the absolute temperature of the surface.
- 5What is a gravitational field?•The region in space where the gravitational force acts on a unit mass.
- 6What is a gravitational field strength?•The gravitational force acting on a unit mass.
- 7What are gravitational field lines?•Field lines which show the direction of the gravitational force.
•They are directed towards the center of the mass. - 8Whats significant about the gravitational field lines around a spherical object?•They are radial, which means that the field lines around a spherical object are non uniform.
- 9What is the exception for earth to have a uniform gravitational field?•By considering a small region such as a playground.
- 10What is Newton's law of gravitation?•The gravitational force between two spherical bodies is directly proportional to the product of their masses.
•The gravitational force is inversely proportional to the square of the distance between the centres. - 11How are stars defined?•Classified into groups according to surface temperature.
- 12What is the significance of stars sharing a surface temperature?•These stars tend to share many other features such as:
-colour
-chemical composition
-age - 13What is the significance of the surface temperature?It helps to determine other features such as:
•colour
•chemical composition
•age - 14How can spectral classes of stars be remembered?Oh Be A Fine Girl, Kiss Me
- 15What are the trends from O to M?•The temperature decreases.
•Colour shifts to red region of visible spectrum.
•Mass decreases.
•Radius decreases.
•Luminosity decreases.
•Duration as a stable star increases. - 16Why does the duration of as a stable star increase when the mass of the star decreases?•There is a very low gravitational pressure or force towards the mantle of the star.
•Hence, nuclear fission takes place a low rate.
•Therefore, less hydrogen nuclei will be burned. - 17What are the trends of hot stars?•More massive
•More luminous
•Release more energy per second. - 18What is the life cycle of an average star?1) Protostar - Stellar nebular
2) Main sequence
3) Planetary nebula
4) White dwarf - 19What is a Protostar?•A collection of Hydrogen and Helium which is the 1st stage of a star.
- 20What is a stable stage?•H fuses with He.
•Inward gravitational pressure and outward radiation pressure are in equilibrium.
•The equilibrium is remained for several billion years. - 21What is a red giant?•Eventually, there will be very little H.
•Due to the vast energy produced, the star expands.
•The expansion causes a temperature drop.
•This state is maintain for 1 billion years only. - 22What is a planetary nebula?•As the star expands, H will start to fuse with He nuclei.
•The result will be an explosion
•The explosion causes fragments of the star to be scattered in space. - 23What is a white dwarf?•When the outward radiation pressure drops, gravity takes hold.
Hence, the star will contract to a smaller size.
•The smaller size causes the star to heat up and be a white dwarf. - 24How can a white dwarf be a brown dwarf? and then a black dwarf?•When a white dwarf runs out of energy it becomes a brown dwarf.
•When a brown dwarf runs out of energy, it becomes a black dwarf. - 25What is the concept of a black dwarf only a theory?•The time taken to form a black dwarf is far longer than that of the universe.
- 26What is the lifecycle of a massive star?1) Protostar - stellar nebula
2) Main sequence
3) Red supergiant
4) Supernova
5) Formation of neutron star or blackhole - 27What is the factor which determines the formation of a super giant?•If the star begins with a mass which is 4 times greater than that of the sun.
- 28What is the consequence of He fusion within a massive star?•Large nuclei of Si, C and O can be made (SiCO).
•This fusion continues until Fe 56 is produced.
•At this point, the star can no longer undergo nuclear fusion so it stops producing energy. - 29How long is the main sequence of a supergiant?•A few million years
- 30What is the importance of the large magnitude of energy released in a supernova?•The energy is used in nuclear reactions.
•The nuclear reactions produced elements heavier than Fe 56.
The supernova also releases cosmic rays. - 31What is the factor which determines the formation of a neutron star or blackhole?•If the central core of the stellar material is more massive than 3 solar masses, it forms a blackhole.
•If the central core of the stellar material is less than or equal to 3 solar masses, it forms a neutron star. - 32What are the common properties of neutron stars and blackholes?•Neither of these are easy to easy to see since they emit little or no light.
- 33What is a neutron star?•Consists of almost entirely neutrons.
•Consequently, it has a high density.
•Has a diameter of 10km. - 34What is the difference between a neutron star and blackhole?•A blackhole is smaller and contains more matter than a neutron star.
•Consequently, a blackhole has a higher density compared to a neutron star.
•The high density of a blackhole causes the gravitational pull of the blackhole to be high. - 35What does the Hertzprung Russell (HR) diagram tell us about the stars present in it?•Relative luminosity
•Surface temperature. - 36What is trigonometric parallax?•A technique used to measure the distance to a nearby star within our galaxy.
- 37What does a trigonometric parallax depend on?•The apparent motion of nearby stars compared to more distant stars, using observations made 6 months apart.
- 38What is called a parallax?•When a nearby object is viewed from two different positions, it will appear to move with respect to a more distant background.
- 39What is the relationship between a parallax angle and a shifting angle?•The parallax angle is twice that of the shifting angle.
- 40How a relatively close star appear as the Earth orbits around the Sun?•It will appear to move across the background of the distant stars.
- 41What is the time period in which we measure the angle to a star? (Parallax angle)•6 months after the first observation.
•A time of 6 months means that the Earth is exactly is on the opposite side of the orbit. - 42What is the distance between two observing positions?•2 A.U.s
- 43What is the angle being measured?•The parallax angle
- 44How can the distance using Trigonometric Parallax be calculated.•Since we have the parallax angle and the distance between the sun and earth, we can apply trigonometry to find the distance.
- 45What is a Cepheid variable star?•A Star which expands and contracts repeatedly.
•Consequently, its luminosity would vary with time. - 46How can the star's distance be determined using Cepheid variable?•Measure the radiation flux on the earth surface.
•Use the period of luminosity variation to determine the average luminosity of the Cepheid.
•Use the Luminosity equation to determine the distance. - 47How can we use standard candles in astrophysics?•We can use candles to model a galaxy.
- 48What is the importance of the Cepheid variable in measuring stars which are 2-3 galaxies away?•Cepheid measurements are used in techniques to measure more distant stars or galaxies.
- 49What is the age of the universe?•13.7 billion years.
- 50How was the universe created?•All matter was concentrated to a tiny dot.
•The big bang caused the expansion of the universe.
•Time and space itself were created with the big bang. - 51What can be said about the tiny dot?•It had an infinite denisty.
•It was extremely hot. - 52What occurs to the average density and temperature as the universe expands?•The average density and temperature decreases as the universe expands.
- 53How can the future of the universe be categorized?•Open universe
•Flat universe
•Close universe - 54What is an open universe?•A universe which keeps expanding.
- 55What is a flat universe?•A universe which expands to a maximum point and stop expanding after that point.
- 56What is a close universe?•A universe which expands to a maximum point and then contracts inwards resulting a big crunch.
- 57What is the criteria which the future of the universe depends on?•Average density of the universe.
•Matter of the universe. - 58How could the universe expansion be stopped or slowed down?•By gravitational force
- 59What is critical density?•The boundary between the open and closed universe.
•It is large enough to prevent the expansion of the universe.
•But not too large for the collapse to take place. - 60What if the average density of the universe is greater than the critical density?•The universe starts to contract and becomes a close universe
- 61What if the average density of the universe is small than or equal to the critical density?•The Universe will expand forever or be an open universe
- 62In terms of atoms, what is critical density?•6 atoms per m^3.
- 63How can universe expansion be observed in the laboratory?•Past a few paper pieces on a balloon and inflate it.
•The distance between the paper pieces increase. - 64What does the balloon, paper pieces and inflation of balloon represent?•Balloon - Universe
•Paper pieces - Galaxies.
•Inflation of balloon - Expansion of universe.
When the universe expands, more space is created between galaxies. - 65What is Hubble's Law?•The recessional velocity of a galaxy is directly proportional to its distance away from us.
- 66How did Edwin Hubble calculate: 1. distance between us and galaxies? 2. Recessional velocity of galaxies?1. Cepheid variable
2. Doppler shift - 67What was the relationship between the recessional velocity and distance between us and galaxies?•Directly proportional
- 68How was the Hubble's constant calculated?•A graph of recessional velocity against distance between earth and galaxy was plotted.
•It is a y=mx graph and the gradient gave the Hubble's constant. - 69Why is there a large uncertainty with the value of Hubble's constant?•The values for recessional velocity and distance between us and the galaxy are approximations.
•Therefore, the recessional velocity and the distance between us and the galaxy have a large uncertainty. - 70What do we use the Hubble's constant for and how does its large uncertainty affect its purpose?•We use the constant to calculate the age of the universe.
•Since the constant has a large uncertainty, the age of the universe has a large uncertainty as well. - 71What do we assume when we calculate the age of the universe?•That the universe has been expanding at a constant rate since the big bang.
- 72What is Doppler's effect?•The apparent change in frequency and wavelength when there is a relative motion between a wave source and an observer.
- 73What is the difference between a red shift and a blue shift?•A red shift occurs when a galaxy travels away from us.
•A blue shift occurs when a galaxy travels towards us. - 74How can the mass of a galaxy be calculated?•By using the actual luminosity and the inverse square law.
•By measuring the period of galaxies and using the centripetal force concept. - 75Which method of calculating the mass of the galaxy was greater?The centripetal force concept gave a large mass than Luminosity.
- 76What was the relationship between the mass of the galaxy calculated from luminosity and the mass of the galaxy calculated using centripetal force?•The Luminosity value is 10% if that of the centripetal force value.
- 77What can be deduced about the relationship?•It provides evidence that the galaxies contain matter which does not emit light.
•This matter was called as dark matter. - 78What could dark matter be comprised of?•Blackholes
•Interstellar gases - 79Can dark matter be seen or detected?•The dark matter should emitt some radiation but it cannot be detected.
- 80What evidence can be provided for big bang?•Since all distant galaxies show red shift, the galaxies are moving away from each other.
•The galaxies move away due to the expansion of the universe.
•Hence, the red shift provides evidence for the big bang.
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- A-Level Physics Flashcards on Gravitational fields, created by Jio Jenassi on 03/02/2016.
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- Jio Jenassi
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