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Advanced Higher Physics > Astrophysics > Flashcards

Astrophysics Flashcards

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1
Q

What is the work done independent on?

A

The path taken

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2
Q

How are satellites kept in orbit around a planet?

A

By the gravitational force, which provided the centripetal force

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3
Q

What is the gravitational potential of a point in space?

A

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

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4
Q

What is the gravitational force at infinity?

A

0N

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5
Q

What is escape velocity?

A

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

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6
Q

What is the difference between special relativity and general relativity?

A

Special relativity occurs in inertial frames of reference

General relativity occurs in non-inertial frames of reference.

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7
Q

What does inertial mean?

A

Non-accelerating

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8
Q

What does non-inertial mean?

A

Accelerating

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9
Q

What is the equivalence principle?

A

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

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10
Q

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

A

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

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11
Q

What curves space time?

A

Mass

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12
Q

What is gravity due to?

A

The curvature of space time

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13
Q

What can a large mass do to light?

A

Make light bend.

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

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14
Q

What is a geodesic?

A

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

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15
Q

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

A

Bend

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16
Q

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

A

High g

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17
Q

What happens to time under the influence of greater gravity?

A

Time runs slower (dilates)

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18
Q

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

A

The time

“The lower, the slower”

19
Q

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

A

The rear

20
Q

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

A

A worldline

21
Q

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

A

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

22
Q

What is a black hole?

A

A compressed star with a very small radius

23
Q

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

A

A very strong gravitational field

They also severely curve/warp space time

24
Q

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

A

A singularity

25
Q

What is the Schwarszchild radius?

A

The distance from the singularity to the event horizon

26
Q

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

A

The speed of light

3x10^8

27
Q

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

A

Frozen

28
Q

What is the definition of luminosity?

A

The total energy radiated per second (or power radiated)

29
Q

What is luminosity dependant on?

A

Radius

Surface temp

30
Q

What is the definition of apparent brightness?

A

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

31
Q

What assumptions do we make about stars?

A

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

32
Q

What is a blackbody?

A

Absorb/emit all wavelengths of radiation

33
Q

Where are stars formed?

A

Interstellar clouds (Nebulae)

34
Q

How are stars formed?

A

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

35
Q

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

A

The P-P chain

36
Q

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

A

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)

37
Q

What are H-R diagrams?

A

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

38
Q

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

A

Main sequence

39
Q

What do main sequence stars do in their core?

A

Fuse hydrogen nuclei into helium nuclei

40
Q

Explain the red giant branch

A

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.

41
Q

Explain helium core fusion

A

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)

42
Q

What does the mass of a star determine?

A

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)

43
Q

What will every star ultimately become?

A

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

Advanced Higher Physics (5 decks)

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