OCR GCSE Physics A: Red-shift, the Big Bang and star formation (J249) – 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 OCR GCSE (9-1) Gateway Science Physics A specification (J249), Version 5.0 (July 2026), for first assessment in 2018. They cover statements P8.3a, P8.3b and P8.3c. All three are printed in bold in the specification and are tested only in the Higher Tier papers, so every question is labelled “(Higher Tier only)”. Read the study guide first, or use the revision notes. Hub: OCR GCSE Physics. Checklist: printable checklist. Find weak spots with the free diagnostics.

Questions

1. (Higher Tier only) Describe what is meant by the red-shift of light from a galaxy. [2]

2. (Higher Tier only) Light from most galaxies is red-shifted.

(a) State what the red-shift of a galaxy tells you about its motion. [1] (b) Predict how the light from a galaxy moving towards us would differ from the light it emitted. [1]

3. (Higher Tier only) The calcium K spectral line is at 393 nm in a laboratory measurement. Astronomers find this line in light from four galaxies.

Galaxy	Distance (million light years)	Observed wavelength (nm)
J	120	396
K	240	400
L	480	407
M	960	420

(a) Explain how the table shows that all four galaxies are moving away from us. [2] (b) State which galaxy is moving away fastest and give a reason. [1] (c) Describe the pattern between distance and speed, and state what it suggests about the universe. [2]

4. (Higher Tier only) A student says, “Red-shift means that the light has slowed down, so it looks redder.” Explain why this is not correct. [2]

5. (Higher Tier only) A balloon with small coins stuck on it is inflated. Explain how this models the motion of galaxies, and state one limitation of the model. [4]

6. (Higher Tier only) Astronomers identify the elements in a galaxy from the pattern of dark lines in its light. Explain how they can tell that the lines in the light from a distant galaxy have been red-shifted. [2]

7. (Higher Tier only) Explain how the expansion of the universe leads to the idea of the Big Bang. [3]

8. (Higher Tier only) Cosmic microwave background radiation (CMBR) is detected from every direction in space.

(a) State the part of the electromagnetic spectrum in which CMBR is found. [1] (b) Explain how the Big Bang model accounts for CMBR. [3]

9. (Higher Tier only) A student writes, “The Big Bang was an explosion at a point in space, and the galaxies have been moving outward from that point ever since. We are near the centre because we see all galaxies moving away from us.” Evaluate the student’s statement. [3]

10. (Higher Tier only) Describe the stages by which a cloud of interstellar dust and gas became the Sun and began releasing energy by fusion. [4]

11. (Higher Tier only) The Sun has stayed about the same size for billions of years.

(a) Name the two effects that are in equilibrium in the Sun. [2] (b) Explain what causes each effect. [2] (c) Explain how this equilibrium would restore itself if the rate of fusion in the core increased slightly. [2]

12. (Higher Tier only) Read the two statements about the early universe.

Statement 1: Light from distant galaxies is red-shifted by more for the galaxies that are further away. Statement 2: Microwaves arrive at Earth from all directions with almost the same intensity.

(a) Explain how each statement is linked to the Big Bang model. [4] (b) Explain why scientists are more confident in the Big Bang model because both statements are supported by observations. [2] (c) A massive star at the end of its life explodes as a supernova. Suggest why this matters for stars and planets that form later. [2]

Answers

1. The wavelength of the light observed is longer than the wavelength emitted [1]. The frequency is lower, so the light is shifted towards the red end of the spectrum [1]. [2] Examiner insight: Naming both wavelength and frequency, with their directions, is clearer than saying the light “goes red”, which describes colour only.

2. (a) The galaxy is moving away from us [1]. (b) Its wavelength would be shorter and its frequency higher than emitted [1]. [2] Examiner insight: For a prediction, say which way each quantity changes; “it would be different” is too vague to credit.

3. (a) Every observed wavelength is longer than 393 nm [1], so each galaxy shows red-shift and is moving away from us [1]. (b) Galaxy M [1]. It has the greatest shift, 420 nm compared with 393 nm, so it has the greatest speed of recession. (c) The further away the galaxy, the larger the red-shift and the faster it moves away; the shift roughly doubles when the distance doubles [1]. This suggests that the universe is expanding [1]. [5] Examiner insight: Quoting values from the table, such as 3 nm for galaxy J and 27 nm for galaxy M, shows that the pattern has been read from the data rather than recalled.

4. Light always travels through space at the same speed, so red-shift is not slowing [1]. Red-shift is a longer wavelength and lower frequency, which happens when the source moves away [1]. [2] Examiner insight: Correcting a statement works best by saying what is wrong and then giving the correct idea; repeating the claim in other words earns nothing.

5. The coins are galaxies and the balloon rubber is space [1]. As the balloon is inflated, every coin moves away from every other coin, and coins that are further apart separate faster [1]. This models the expansion of the universe, where the same pattern is seen from any galaxy [1]. Limitation: for example, the balloon expands into surrounding air but the universe does not expand into anything known, or the balloon surface is two-dimensional but space is three-dimensional (any sensible one) [1]. [4] Examiner insight: Three marks go to the model itself (galaxies are coins, spaces stretch, further coins move faster) and one to the limitation, so a separate sentence for the limitation is worth writing.

6. Each element produces lines at known wavelengths in the laboratory, so the pattern of lines can be recognised [1]. In the galaxy the same pattern is seen, but all the lines are at longer wavelengths than the laboratory values [1]. [2] Examiner insight: The comparison with laboratory values is the key point; a pattern “looking different” does not show a systematic shift.

7. Galaxies are moving apart, so the universe is expanding [1]. In the past galaxies were therefore closer together [1]. Going back far enough, all matter and space were in a very small, hot, dense region, and the expansion since then is the Big Bang [1]. [3] Examiner insight: Answers that move in a clear order (observation, then running it backwards, then the start) tend to be easier to credit than answers that just assert “it began small”.

8. (a) Microwaves [1]. (b) The early universe was extremely hot and filled with radiation of very short wavelength [1]. As the universe expanded, the wavelengths of this radiation were stretched [1]. Today it is seen from all directions as microwaves, which is what CMBR is [1]. [4] Examiner insight: Mention stretching of wavelength by expansion. Saying that CMBR is “heat left over” without the change in wavelength leaves out the main link.

9. There was no explosion at a point in space: the Big Bang was the expansion of space itself [1]. There is no centre, because observers in every galaxy see the other galaxies moving away from them [1]. So we are not near a centre; the pattern is what is expected for any galaxy in an expanding universe [1]. [3] Examiner insight: An evaluate answer should address each part of the statement. Saying “wrong” without saying why is not enough.

10. A cloud of dust and gas, mostly hydrogen, is pulled together by gravity [1]. As the cloud contracts, gravitational potential energy is transferred to thermal energy, so the temperature rises [1]. The centre becomes hot and dense enough for hydrogen nuclei to fuse into helium [1]. Fusion releases energy, and the star settles into a stable state [1]. [4] Examiner insight: Four marks need four separate stages; naming gravity, rising temperature, fusion and stability in order covers them.

11. (a) Gravitational collapse (inward) [1] and expansion due to energy released by fusion (outward) [1]. (b) Gravity pulls the Sun’s matter towards the centre [1]. Energy released by fusion heats the gas and makes it expand outward [1]. (c) The core would heat up and expand slightly, so the density falls [1]. Fusion then slows down, returning the star towards its original size [1]. [6] Examiner insight: The answer to (c) should state the chain of cause and effect; “it self-corrects” is not an explanation.

12. (a) Statement 1: it shows that galaxies are receding faster the further away they are, so the universe is expanding, as the Big Bang model predicts [2]. Statement 2: CMBR is radiation left from the hot early universe, stretched into microwaves by expansion [1], and it is expected from all directions [1]. (b) Two different kinds of evidence both agree with what the model predicts [1], so it is less likely that both are the result of chance or error [1]. (c) A supernova scatters heavier elements through space [1]. Later stars and planets can form from dust and gas that contains these elements [1]. [8] Examiner insight: “Explain how each statement is linked” asks for two links; answers that describe the statements again without connecting them to the model do not answer the question.

Where marks are usually lost

• Describing red-shift as “the colour changes” without wavelength and frequency.
• Swapping which of wavelength and frequency increases.
• Saying red-shift shows that a galaxy is far away, not that it is moving away.
• Giving distance-speed patterns without quoting values from the table.
• Describing the Big Bang as an explosion into space or giving it a centre.
• Explaining CMBR without saying that expansion stretched the wavelengths.
• Writing “gravity and fusion balance” without saying that fusion releases the energy that causes expansion.
• Saying that light “slows down” in red-shift.

Next steps

• Revision notes
• Study guide
• OCR GCSE Physics hub
• Printable checklist
• All free 10-minute diagnostics
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Official syllabus

OCR, GCSE (9-1) Gateway Science Physics A (J249) specification, Version 5.0 (July 2026), for first assessment in 2018, topic P8.3 Beyond Earth, statements P8.3a to P8.3c.