AQA GCSE Physics Physics Paper 2 (Higher), November 2021: Question 3
7 marks · Standard Demand difficulty · Short Answer
Explain stellar stability on the main sequence, describe the subsequent life cycle stages for a Sun-like star, and interpret a speed-distance graph for galaxies to determine red-shift properties.
Practise this questionQuestion
Question text
03 A main sequence star in a distant galaxy is the same size and mass as the Sun.
03.1 Explain why the star is stable while it is in the main sequence stage of its life cycle.
[2 marks]
03.2 Describe what will happen to the star between the main sequence stage and the end
of the star’s life cycle.
You should include the names of the stages in the life cycle of the star.
[3 marks]
03.3 Figure 5 shows how the speed of galaxies moving away from Earth varies with the
distance of the galaxies from Earth.
Figure 5
Which galaxy would show the smallest observed change in the wavelength of
visible light?
Give a reason for your answer.
[2 marks]
Tick ( ) one box.
A B C D
Reason
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 gravitational force inwards and allow fusion energy for fusion 1 AO1
forces as a result of fusion reactions outwards 4.8.1.1
reactions outwards
allow radiation pressure for
fusion reactions outwards
are in equilibrium / balanced dependant on scoring 1st mark 1
point
allow for 1 mark forces are in
equilibrium
03.2 (the star will) expand to become the answers must be in the 1 AO1
a red giant correct sequence to score all 4.8.1.2
3 marks
(the star will) collapse to allowed outer layers ejected for 1
become a white dwarf collapsed
(the star will) cool to become a 1
black dwarf
if no other marks score, allow
red giant, white dwarf, black
dwarf in the correct order for
1 mark
03.3 A 1 AO3
4.8.2
it is (moving away from Earth) reason only scores if A is 1
the slowest chosen
or
it is the closest (to the Earth)
Total 7
How to answer it
Stellar Evolution and Red-Shift Study Guide
What this question tests
This question assesses your knowledge of stellar physics (specifically the forces acting inside a main sequence star), the stages in the life cycle of a star with a mass similar to the Sun, and the interpretation of graphical data relating to galaxy speed, distance, and red-shift.
Stability of a Main Sequence Star
✅ Correct Answer
1. Gravitational force inwards is balanced by fusion reactions / radiation pressure outwards.
2. The forces are in equilibrium.
💡 Key Knowledge
- A star is locked in a constant tug-of-war between gravity pulling mass inward and thermal/radiation pressure pushing outward.
- During the main sequence, hydrogen fusion in the core provides the outward pressure.
🧠 Exam Technique
Mentioning both opposing forces (inwards vs outwards) is required for the first mark. The second mark is conditional on mentioning that these forces are balanced or in equilibrium.
❌ Common Errors
Students often forget to state that the forces are balanced, or incorrectly state that gravity stops acting once the star is formed.
Life Cycle of a Sun-Sized Star
✅ Correct Answer
1. Expands to become a red giant.
2. Collapses to become a white dwarf.
3. Cools to become a black dwarf.
💡 Key Knowledge
- Stars similar in mass to the Sun do not go supernova.
- As core fusion changes, the outer layers expand and cool (red giant), then outer layers are shed leaving a hot core (white dwarf), which eventually fades (black dwarf).
🧠 Exam Technique
The stages must be in the correct sequence to score all 3 marks. If the sequence is mixed up, examiners may only award 1 consolation mark if all three correct terms appear anywhere in your answer.
❌ Common Errors
Confusing the life cycle of a Sun-sized star with a massive star (e.g., mentioning supernovas, neutron stars, or black holes for a Sun-like star).
Galaxies, Distance, and Red-Shift
✅ Correct Answer
Galaxy: A
Reason: It is moving away from Earth the slowest (or it is the closest to the Earth).
💡 Key Knowledge
- Red-shift is directly proportional to the distance of a galaxy from Earth.
- A smaller speed away from Earth means a smaller red-shift, resulting in the smallest observed change in the wavelength of visible light.
🧠 Exam Technique
This is a 2-part dependent question: the reason mark only scores if galaxy A is correctly selected first. Always check both axes of graphs carefully before answering.
❌ Common Errors
Choosing galaxy D because it is furthest away, misinterpreting "smallest change" to mean maximum distance instead of minimum speed/distance.
Topics
Physics · P8: Space Physics (physics only)
Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 2 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.