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A Level-Physics > Module 5 Part 2- Astrophysics > Flashcards

Module 5 Part 2- Astrophysics Flashcards

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1
Q

What is a gravitational field

A

A gravitational field is an area of attraction created by a mass which attracts other masses-every mass has a gravitational field but it is usually negligible unless it is a massive object like the earth

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2
Q

What is gravitational field strength-g

A

Gravitational field strength is the force experienced per unit mass. It is also a vector quantity which acts towards the centre of mass and is indirectly proportional to the distance from the centre

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3
Q

Gravitational field lines around a mass are:

A

Radial

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4
Q

What does it mean that the force lines on a mass are radial

A

The lines get further from each other the further away from the mass which shows how the field decreases in strength

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5
Q

What is G and what is the value of it (in formula book)

A

G is the universal gravitational constant and it has a value of 6.67x10^-11

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6
Q

What is newtons law of gravitation and what is the equation

A

The force between two masses is directly proportional to the product of their masses and indirectly proportional to the distance between them squared
F=-GMm/r^2

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7
Q

What is the equation for gravitational force

A

F=(-GMm)/r^2

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8
Q

What is a uniform gravitational field and give an example

A

A gravitational field where the value of g is the same everywhere for example on the surface of earth

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9
Q

What is keplers first law

A

A planets orbit is elliptical with the object it is orbiting as one of the foci

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10
Q

What is keplers second law

A

A line segment joining the planet to the sun sweeps out equal areas during equal intervals in time

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11
Q

What is keplers third law and what is the equation for it

A

The square of the orbital period of a planet is proportional to the average distance between the masses cubed
T^2=(4π^2/GM) r^3

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12
Q

What is the equation for the speed of a planet and how do you arrive there

A

v= √(GM/r), this equation is arranged when you consider the orbit as a circle and use the circular motion equation for centripetal force and set it equal to the gravitational force equation

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13
Q

What is a satellite

A

A satellite is any object which orbits around another object usually of much larger mass (earth is a satellite to the sun)

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14
Q

What are the types of orbit for satellites (earth satellites)

A

Polar orbit, equatorial orbit, low earth orbit and geostationary orbit

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15
Q

What is a geostationary orbit

A

An orbit which has a period of 24 hours, satellites in this orbit spin around the earth at the same rate the earth spins and therefore stay in the same place in the sky

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16
Q

What is gravitational potential

A

Gravitational potential is defined as the work done per unit mass to move that object to that point from ‘infinity’ which essentially means from a point where g is zero

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17
Q

What is the equation for gravitational potential

A

V=(-GM)/r

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18
Q

What does perihelion and aphelion mean

A

Part of orbit which is closer to star-perihelion
Part of orbit which is further from star-aphelion

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19
Q

What are the three assumptions of cosmological principle

A

The universe is homogeneous-equal density
The universe is isotropic-same in all directions
The universe has the same laws of physics everywhere

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20
Q

What is an AU

A

AU=astronomical unit which is the distance from the earth to the sun

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21
Q

What is a ly

A

ly=light year which is the distance light travels in one year

22
Q

What is an arc minute and arc second

A

An arc minute is 1/60 of a 1 degree angle
An arc second is 1/60 of an arc minute
Therefore an arcsecond is 1/3600 of a degree

23
Q

What is a pc

A

pc=parsec
A parsec is the distance that, when combined with one astronomical unit in a 90 degree triangle, creates an angle of 1 arcsecond

24
Q

What is parralax

A

Parallax is the apparent change in an objects position due to a change in the viewing position

25
Q

What is stellar parallax and how does it work

A

Stellar parallax is a technique which utilises the effect of parallax to measure the distance of stars less than 100 pc away.
It works by recording the position of a star relative to the ‘fixed’ position of other stars very far away at different points in the year.
This data is then used to calculate the parallax angle in arcseconds

26
Q

What is the equation that links distance (in parsecs) and parallax angle

A

d=1/p when p is in arc seconds (hence the terms par-secs)

27
Q

What is gravitational potential

A

Gravitational potential energy per unit mass (similar to potential difference)

28
Q

What is the relationship between g and r inside and outside a planet

A

Inside: g∝r
Outside: g∝1/r^2

29
Q

Gravitational potential is the amount of energy needed to move an object of one kilogram from a point of

A

infinity

30
Q

What is escape velocity

A

Escape velocity is the velocity needed to escape a gravitational field

31
Q

What is the equation for escape velocity and how do you arrive there (show working)

A

V=(2GM/r)^1/2
Set the equation for kinetic energy equal to the equation for gravitational potential energy and re arrange

32
Q

What are the stages of a stars life cycle and briefly explain them

A

Nebulae-cloud of dust and gas
Protostar-hot ball of dust and gas due to friction
Main sequence-hot and dense enough ball to begin nuclear fusion
Red giant-hydrogen fuel runs out and star expands due to heavier elements being used
White dwarf-all fuel runs out and star contracts to become a small dense mass

33
Q

What is the Chandrasekhar limit and explain

A

The threshold mass for a star to be able to overcome the electron degeneracy pressure and fuse elements up to iron, causing a red super giant
Given the quantity 1.44M where M is the mass of the sun

34
Q

What happens to a star if it becomes a red super giant

A

The red super giant will use its fuel until it runs out and causes a supernova
If the star is between 1.44M-2M it will become a neutron star
If the star is above 2M it will overcome the neutron degeneracy pressure and become a black hole

35
Q

What are the three types of light unit

A

Luminous emittance-Lux
Luminous flux-Lumen
Luminous intensity-Candela

36
Q

What is the brightness of a star dependent on (when viewed from earth)

A

The luminosity and the distance

37
Q

What is the Hertzsprung-Russel diagram

A

A graph that plots the luminosity against the temperature of a star

38
Q

What are the seven categories on the Hertzsprung Russel diagram and what do they equate to

A

O-He plus, He, H
B-He, H
A-H, ionised metals
F-ionised metals
G-metals
K-neutral metals
M-neutral atoms

39
Q

What would be found in the top left of the Hertzsprung Russel diagram

A

Blue giants

40
Q

What would be found in the top right of the Hertzsprung Russel diagram

A

Red super giant

41
Q

What would be found in the bottom left of the Hertzsprung Russel diagram

A

White dwarf

42
Q

What would be found in the mid right of the Hertzsprung Russel diagram

A

Red giant

43
Q

When an electron moves to a higher energy level it is

A

Excited

44
Q

When an electron moves to a lower energy level it is

A

Relaxed

45
Q

What is a black body

A

An idealised body that does not reflect of transmit, it only absorbs it and hence is called black.
Therefore light of any wavelength that is shone on a black body will disappear inside the black body and it’s energy will be absorbed.

46
Q

What happens when a black body is heated above absolute zero

A

This causes the electrons (and protons) to oscillate in the EM field which causes light to be emitted-aka black body radiation

47
Q

What is wiens law + equation

A

The hotter a black body is the shorter the maximum wavelength

48
Q

What is Stefans law + equation (attack on titan)

A

The larger the surface area of the star, the larger luminosity (power) it emits
L=A x σ x T^4
(where σ is the Stefan constant)

49
Q

What is the Doppler effect

A

The apparent change in a wave’s frequency due to relative motion between the source of the wave and the observer

50
Q

What is the name for the Doppler effect for light which provides evidence for the Big Bang

A

Red shift

51
Q

What is hubbles law + equation

A

The further a galaxy is away, the greater the red shift will be
V=Ho x d

52
Q

What are two pieces of evidence for the big bang

A

Red shift
Cosmic microwave background radiation

A Level-Physics (8 decks)

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