OxfordAQA International GCSE Physics: Life cycle of a star (9203) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions follow the OxfordAQA International GCSE Physics (9203) specification, for exams May/June 2018 onwards, section 3.8.1 (Life cycle of a star, statements a to i). The qualification is untiered. Links: study guide, revision notes, course hub, printable checklist and the 10-minute diagnostics. Where a question needs data, it is supplied in the question. One year is 3.156 × 10⁷ s.

Questions

1. (a) State the force that pulls dust and gas together to form a star. [1] (b) Name the two elements that make up most of this dust and gas. [1]

2. (a) Name the nuclear process that releases energy in a main sequence star. [1] (b) State which nuclei fuse, and which nuclei they make. [1]

3. Explain why a main sequence star stays the same size for millions of years. [3]

4. (a) State which part of a star has the greatest temperature and density. [1] (b) State what is mainly happening in that part. [1] (c) A star has a greater mass than the Sun. Compare the heaviest nuclei its core can make with those in the Sun. [1]

5. A star has the same mass as the Sun. (a) Put these stages in the order the star passes through them after the main sequence: black dwarf, white dwarf, red giant. [2] (b) Explain why this star will not become a supernova. [1]

6. A star with a mass much greater than the Sun has used up the hydrogen in its core. Describe what happens next, up to the final remnants. [4]

7. Data supplied: the Sun spends 10 000 million years on the main sequence. A star with 15 times the Sun’s mass spends 12 million years on the main sequence. (a) Calculate how many times longer the Sun lasts. [2] (b) The larger star has 15 times as much fuel. Calculate how many times faster it uses its fuel. [2] (c) Explain why a more massive star has a shorter life even though it has more fuel. [2]

8. Data supplied: a main sequence star gives out 7.6 × 10²⁶ J each second. Fusing 1 kg of hydrogen releases 6.4 × 10¹⁴ J. The star has 3.0 × 10²⁹ kg of hydrogen available as fuel. (a) Calculate the mass of hydrogen fused each second. [2] (b) Calculate how long the fuel lasts, in years. [3] (c) State what your answer shows about the star’s energy output. [1]

9. The early universe contained only hydrogen. Lead is much heavier than iron. A sample of lead is used in a school laboratory. (a) Explain why the universe now contains many different elements. [4] (b) State where lead nuclei were formed and how they reached the cloud that formed the Solar System. [2]

10. A student draws a life-cycle chart. Branch 1 (star like the Sun): main sequence, red giant, supernova, neutron star. Branch 2 (star much more massive than the Sun): main sequence, red supergiant, white dwarf, black dwarf. (a) Identify the mistakes in the chart. [2] (b) Write out the correct sequence for each branch. [4]

11. Explain how the life of a star much more massive than the Sun differs from the life of a star like the Sun, and why mass has this effect. [6]

12. Describe the life of a star about 15 times the mass of the Sun from the cloud it forms in to its end, and explain how the star’s end affects the elements found elsewhere in the universe. [8]

Answers

1. (a) Gravity (gravitational attraction) [1]. (b) Hydrogen and helium [1]. [2] Examiner insight: “Gravity” alone is enough for part (a); naming magnetism or electrostatic force is a common slip, and part (b) needs both elements.

2. (a) Nuclear fusion [1]. (b) Hydrogen nuclei fuse to make helium nuclei [1]. [2] Examiner insight: Give the direction of the change. “Helium fuses to hydrogen” or “atoms split” would lose credit, and fission is a different process.

3. Gravity pulls the star’s material inwards [1]. The very hot gas from fusion in the core pushes outwards [1]. The two forces are balanced, so the size stays steady [1]. [3] Examiner insight: Name both forces and say they are balanced. Writing that fusion has stopped, or that “gravity balances fusion” with no outward effect named, leaves the explanation incomplete.

4. (a) The core (centre) [1]. (b) Most of the nuclear fusion [1]. (c) A star of greater mass has a hotter core, so it can make heavier nuclei than the Sun [1]. [3] Examiner insight: For a comparison, state both sides: heavier nuclei for the larger star. A one-sided statement such as “heavy nuclei” may not show the comparison asked for.

5. (a) Red giant, then white dwarf [1], then black dwarf [1]. (b) Its mass is too small / it follows the smaller-star route to a white dwarf [1]. [3] Examiner insight: Give all three stages in the right order, since a stage out of place changes the sequence. In part (b), refer to the star’s mass.

6. It swells to become a red supergiant [1]. It expands, cools and turns red, and helium fuses to carbon and then heavier nuclei such as nitrogen and oxygen [1]. The outer layers are blasted away in a supernova [1]. The core collapses and ends up as a neutron star or a black hole, according to its mass [1]. [4] Examiner insight: Both remnants are needed, with the mass link. Do not add a white dwarf, which belongs to the smaller-star route.

7. (a) 10 000 ÷ 12 = 833.3 [1], so about 833 times longer [1]. (b) Rate ratio = fuel ratio × lifetime ratio = 15 × 833.3 [1] = 12 500 times faster [1]. (c) The more massive star has a hotter core [1], so it fuses hydrogen much faster and uses up its fuel sooner [1]. [6] Examiner insight: In part (b) multiply the fuel ratio by the lifetime ratio; just reusing 833 shows only the lifetime comparison. Give the working before the answer.

8. (a) mass per second = 7.6 × 10²⁶ ÷ 6.4 × 10¹⁴ [1] = 1.19 × 10¹² kg (about 1.2 × 10¹² kg) [1]. (b) time = 3.0 × 10²⁹ ÷ 1.19 × 10¹² = 2.5 × 10¹⁷ s [1]; years = 2.5 × 10¹⁷ ÷ 3.156 × 10⁷ [1] = 8.0 × 10⁹ years [1]. (c) The fuel lasts billions of years, so the star can keep its energy output going for millions of years [1]. [6] Examiner insight: Keep units on each step (kg per second, then seconds, then years). A final answer left in seconds loses the conversion step. Give 2 significant figures to match the data.

9. (a) Stars formed from the hydrogen [1]. Fusion in stars made helium and then heavier nuclei, so new elements were made [1]. Any element heavier than iron comes from a supernova [1]. The explosion distributes the elements through the universe [1]. (b) Lead nuclei were formed in a supernova [1]; the explosion spread them through space, where the material became part of the cloud of dust and gas that formed the Solar System [1]. [6] Examiner insight: An explanation of origin needs both parts: where the elements are made and how they travel. Answers that stop at “made in stars” miss the distribution point.

10. (a) The supernova and neutron star are on the wrong branch (the Sun’s route has no supernova) [1]. The white dwarf and black dwarf are on the wrong branch (a much more massive star ends in a supernova) [1]. (b) Sun-like: main sequence, red giant [1], white dwarf [1], black dwarf. Much more massive: main sequence, red supergiant [1], supernova, then neutron star or black hole [1]. [6] Examiner insight: Correct each branch in full. Moving one stage but leaving another in the wrong place is not a full correction.

11. Both stars start by being pulled together by gravity and spend most of their life on the main sequence fusing hydrogen to helium [1]. The more massive star has a hotter core [1], so it can make heavier nuclei [1] and uses its fuel faster, so its main sequence life is shorter [1]. After the main sequence the Sun-like star becomes a red giant, white dwarf and black dwarf [1]; the much more massive star becomes a red supergiant, supernova, then neutron star or black hole. The route depends on mass [1]. [6] Examiner insight: A comparison needs both stars named in each point. Say the life cycle is set by mass, and give the specific stages for each route rather than “it explodes”.

12. Gravity pulls the dust and gas (mainly hydrogen and helium) together; the material gets denser and hotter [1]. A star forms with fusion of hydrogen to helium in the core [1]. On the main sequence the forces are balanced and it is stable [1]. When hydrogen runs out it swells to a red supergiant, which expands, cools and turns red [1]. Helium fuses to carbon and heavier nuclei [1]. The outer layers are blasted away in a supernova [1]. The core collapses, leaving a neutron star or a black hole according to its mass [1]. The explosion distributes the elements it made, and elements heavier than iron formed in the supernova, through the universe [1]. [8] Examiner insight: Put the stages in time order and link each to the next. Five or six stages named without the link between them tend to earn fewer marks than a clear sequence that ends with the distribution of elements.

Where marks are usually lost

• Naming the wrong route: giving the Sun a supernova or a larger star a white dwarf.
• Saying fusion stops on the main sequence, instead of saying the forces are balanced.
• Naming gravity but not the outward effect from the hot gas.
• Dropping the mass link when asked why two stars differ.
• Giving only a neutron star or only a black hole as the end of a supernova.
• Forgetting to convert seconds to years, or to multiply the fuel ratio by the lifetime ratio.
• Writing that all elements are made in supernovae.
• Describing the black dwarf as a black hole.
• Leaving out the distribution of elements by the explosion in an origins answer.

Next steps

• Revise with the revision notes and re-read the study guide.
• See the OxfordAQA IGCSE Physics hub and the printable checklist.
• Try all free 10-minute diagnostics at /diagnostics/.
• Book a free trial class at /trial/.

Official syllabus

OxfordAQA International GCSE Physics (9203), specification version 5.2, for exams May/June 2018 onwards, published by OxfordAQA. Section 3.8.1, Life cycle of a star.