Stellar Evolution (Edexcel IGCSE Physics)
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What property of a star does its colour tell us?
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What property of a star does its colour tell us?
The colour of a star tells us about its surface temperature.
True or False?
The hottest stars are red.
False.
The hottest stars are blue, whereas the coolest stars are red.
Which has a hotter surface temperature, a red giant or a white dwarf?
A white dwarf has a hotter surface temperature than a red giant.
True or False?
As a star expands, its surface cools and becomes redder.
True.
As a star expands, its surface cools and becomes redder.
True or False?
All stars form from a cloud of dust and gas which becomes a protostar and then a main sequence star.
True.
All stars follow the same initial stages in their life cycle:
Nebula (cloud of dust and gas)
Protostar
Main sequence star
The stages that follow depend on the mass of the main sequence star that forms.
What forces, including their direction, act when a star is in a stable state?
The forces acting on a star in a stable state are:
Inward gravitational force
Outward pressure due to fusion reactions
Name the stages, in the correct order, in the life cycle of a star similar to the Sun.
The stages, in the correct order, in the life cycle of a star similar to the Sun are:
Nebula (cloud of dust and gas)
Protostar
Main sequence star
Red giant
White dwarf
When does a protostar become a main sequence star?
A protostar becomes a main sequence star when nuclear fusion reactions are initiated in its core and the inward force of gravity is balanced by the outward pressure from the fusion reactions.
When does a main sequence star turn into a red giant?
A main sequence star turns into a red giant when hydrogen in the star's core begins to run out and the star begins to fuse helium into heavier elements.
True or False?
A high-mass star will eventually explode as a supernova and become a white dwarf.
False.
A high mass star will eventually explode as a supernova and become a neutron star or a black hole.
Name the stages, in the correct order, in the life cycle of a star with a mass larger than the Sun.
The stages, in the correct order, in the life cycle of a star with a mass larger than the Sun are:
Nebula (cloud of dust and gas)
Protostar
Main sequence
Red supergiant
Supernova
Black hole, or neutron star
What is a supernova?
A supernova is a large exploding star.
Under what conditions does a supernova occur?
A supernova occurs when a star much more massive than the Sun reaches the end of its red supergiant stage. It collapses, becomes very unstable and explodes.
Define luminosity.
Luminosity is the total amount of light energy emitted by a star.
What is apparent magnitude?
Apparent magnitude is the perceived brightness of a star as seen from Earth.
What is absolute magnitude?
Absolute magnitude is a measure of how bright stars would appear if they were all placed the same distance away from the Earth.
What two factors influence the apparent magnitude of a star?
The two factors that influence the apparent magnitude of a star are
the luminosity of the star
the distance of the star from Earth
What does the apparent magnitude scale show?
The apparent magnitude scale shows that:
the brighter the star, the lower the apparent magnitude
the dimmer the star, the higher the apparent magnitude
Why is it difficult to measure the brightness of stars directly?
It is difficult to measure the brightness of stars directly because a distant bright star might appear to have the same brightness as a nearby dim star.
True or False?
An object with an apparent magnitude of +10 is brighter than an object with an apparent magnitude of -10.
False.
An object with an apparent magnitude of +10 is dimmer than an object with an apparent magnitude of -10.
This is because the brighter the star, the smaller the magnitude.
What is a Hertzsprung-Russell (HR) diagram?
The Hertzsprung-Russell (HR) diagram is a plot of a star's luminosity on the y-axis and its surface temperature on the x-axis.
Which star on the H-R diagram has the highest surface temperature, A, B, C or D?
The star with the highest surface temperature is star B.
The hottest stars are located towards the left side of the H-R diagram.
Which star on the H-R diagram has the lowest surface temperature, A, B, C or D?
The star with the coolest surface temperature is star D.
The coolest stars are located towards the right side of the H-R diagram.
Which star on the H-R diagram is the brightest, A, B, C or D?
The brightest star is star A.
The brightest stars are found near the top of the H-R diagram.
Which star on the H-R diagram is most similar to the Sun, A, B, C or D?
The most similar star to the Sun is star C.
The luminosity scale is given in solar units, where the luminosity of the Sun = 1
Where is the main sequence located on the H-R diagram?
On the H-R diagram, main sequence stars are stars found in a band from the top left to the bottom right.
Where are white dwarfs located on the H-R diagram?
On the H-R diagram, white dwarfs are located below the main sequence and slightly to the left.
Where are red giants located on the H-R diagram?
On the H-R diagram, red giants are located above the main sequence and slightly to the right.
What type of stars are the hottest and dimmest on the H-R diagram?
The hottest and dimmest stars on the H-R diagram are white dwarfs.
What type of stars are the coolest and brightest on the H-R diagram?
The coolest and brightest stars on the H-R diagram are red supergiants.