Astrophysics

Question 1

What is the work done independent on?

Answer 1

The path taken

Question 2

How are satellites kept in orbit around a planet?

Answer 2

By the gravitational force, which provided the centripetal force

Question 3

What is the gravitational potential of a point in space?

Answer 3

The work done moving 1kg from infinity to that point.

Question 4

What is the gravitational force at infinity?

Answer 4

0N

Question 5

What is escape velocity?

Answer 5

The minimum velocity required to allow a mass to escape a gravitational field to infinity with zero kinetic energy and zero potential energy.

Question 6

What is the difference between special relativity and general relativity?

Answer 6

Special relativity occurs in inertial frames of reference

General relativity occurs in non-inertial frames of reference.

Question 7

What does inertial mean?

Answer 7

Non-accelerating

Question 8

What does non-inertial mean?

Answer 8

Accelerating

Question 9

What is the equivalence principle?

Answer 9

It is not possible to distinguish between the effects on an observer in a uniform gravitational field or at a constant acceleration

Question 10

What happens to the effects of gravity when an object in freefall experiences ‘weightlessness’?

Answer 10

The effects of gravity are exactly equilavent to the effects of acceleration

Question 11

What curves space time?

Answer 11

Mass

Question 12

What is gravity due to?

Answer 12

The curvature of space time

Question 13

What can a large mass do to light?

Answer 13

Make light bend.

The light still travels in a straight line but space time has curved due to the large mass.

Question 14

What is a geodesic?

Answer 14

The shortest distance between two points in space time that light/objects follow.

Question 15

What does light do according to an observer moving at a high speed (due to the equilavence principle)?

Answer 15

Bend

Question 16

Does light bend when there is a high or low gravitational field strength?

Answer 16

High g

Question 17

What happens to time under the influence of greater gravity?

Answer 17

Time runs slower (dilates)

Question 18

What does the altitude (height) of an object above a planets surface effect?

Answer 18

The time

“The lower, the slower”

Question 19

Does time run slower at the front or rear of a spacecraft?

Answer 19

The rear

Question 20

What is a line drawn on a space time diagram called?

Answer 20

A worldline

Question 21

What causes a star to collapse into a very small radius?

Answer 21

It runs out of fuel and gravitational compressions cause it to collapse.

Question 22

What is a black hole?

Answer 22

A compressed star with a very small radius

Question 23

What do black holes have due to their high density/large mass?

Answer 23

A very strong gravitational field

They also severely curve/warp space time

Question 24

What is the point of infinite density in the centre of a black hole called?

Answer 24

A singularity

Question 25

What is the Schwarszchild radius?

Answer 25

The distance from the singularity to the event horizon

Question 26

What is the escape velocity from the event horizon of a black hole equal to?

Answer 26

The speed of light | 3x10^8

Question 27

What does time appear to be at the event horizon of a black hole for a distant observer?

Answer 27

Frozen

Question 28

What is the definition of luminosity?

Answer 28

The total energy radiated per second (or power radiated)

Question 29

What is luminosity dependant on?

Answer 29

Radius | Surface temp

Question 30

What is the definition of apparent brightness?

Answer 30

The amount of energy per second (power) detected per unit area

Question 31

What assumptions do we make about stars?

Answer 31

They’re perfectly spherical They have a uniform surface temperature They are perfect ‘black-bodies’

Question 32

What is a blackbody?

Answer 32

Absorb/emit all wavelengths of radiation

Question 33

Where are stars formed?

Answer 33

Interstellar clouds (Nebulae)

Question 34

How are stars formed?

Answer 34

In nebulae Gravitational forces cause particles to be pulled into a central core When the core is hot enough to sustain nuclear fusion, the outwards thermal pressure is balanced by inwards gravitational force

Question 35

What process involves hydrogen nuclei in the sun undergoing nuclear fusion into helium?

Answer 35

The P-P chain

Question 36

What are the three stages of the P-P chain?

Answer 36

Two hydrogen nuclei combine to form deuterium nucleus - positron and neutrino are produced Deuterium combines with a proton to produce helium-3 and gamma rays Two helium-3 nuclei combine to form helium-4 nucleus and two protons (which may cause further P-P chains)

Question 37

What are H-R diagrams?

Answer 37

Scattergraphs of star luminosity against surface temp, they allow stars to be given classifications

Question 38

What type of star accounts for 90% of stars in the universe?

Answer 38

Main sequence

Question 39

What do main sequence stars do in their core?

Answer 39

Fuse hydrogen nuclei into helium nuclei

Question 40

Explain the red giant branch

Answer 40

Hydrogen fusion in core of star supplies energetic to maintain the outwards thermal pressure that balances inwards gravitational forces When hydrogen is depleted in core, nuclear fusion in core stops Hydrogen in the shell surrounding core continues fusing, adding more helium to core Gravitational forces cause core to contract, therefore heating core Outwards thermal pressure increases, therefore volume (radius) of star increases Surface temperature decreases as surface area increases, therefore star enters red giant/supergiant region of H-R diagram.

Question 41

Explain helium core fusion

Answer 41

As the sun becomes a red giant, the mass of helium in the core will increase Core will continue to contract Core temperature will increase until helium begins fusing (into carbon)

Question 42

What does the mass of a star determine?

Answer 42

It’s lifetime Stars with a large mass have more fuel but deplete faster (moving from main sequence to red giant on H-R diagram)

Question 43

What will every star ultimately become?

Answer 43

A white dwarf (low/medium mass star) A neutron star (high mass star) A black hole (high mass star)