OCR GCSE Physics A: Radiation from bodies, the solar system and orbits (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 cover statements P8.3d, P8.3e, P8.3f, P8.3g and P8.3h of OCR GCSE (9-1) Gateway Science Physics A (J249), Version 5.0 (July 2026). Every question is Higher Tier only. Learn the content first in the study guide or the revision notes. The course hub, printable checklist and free 10-minute diagnostics are linked for planning.

Questions

1. (Higher Tier only) State two ways in which the radiation emitted by a body changes when its temperature increases. [2]

2. (Higher Tier only) A steel bar is heated slowly in a furnace. At first it gives out no visible light. Later it glows dull red, and later still it glows yellow-white. Explain these observations. [3]

3. (Higher Tier only) Describe three differences between the inner planets and the outer planets of the solar system. [3]

4. (Higher Tier only) Two artificial satellites orbit Earth. One is in a geostationary orbit and one is in a polar orbit.

(a) State two features of a geostationary orbit. [2] (b) Give one use of a polar satellite and explain why its orbit suits that use. [2]

5. (Higher Tier only) A satellite moves in a circular orbit of radius 7.4 × 10⁶ m. It completes one orbit in 6330 s. Calculate its speed. Give your answer to 3 significant figures. [3]

6. (Higher Tier only) A satellite orbits Earth in a circle at constant speed. A student says that no force is needed because the speed does not change. Explain why the student is wrong, and state the direction of the force. [4]

7. (Higher Tier only) A satellite is in a stable circular orbit.

(a) A second satellite orbits closer to Earth. State how its speed compares and explain why. [2] (b) Engineers fire a thruster on the first satellite so that it speeds up. Explain what must happen to the radius of a stable orbit at the new speed. [2]

8. (Higher Tier only) A flat metal panel on a spacecraft absorbs radiation at 320 W and emits radiation at 250 W. Calculate the energy transferred to the panel in 15 minutes. [3]

9. (Higher Tier only) Two identical tins of water start at the same temperature and stand in bright sunshine. One tin has a matt black surface. The other has a shiny silver surface. Explain why, after an hour, the black tin is warmer. [3]

10. (Higher Tier only) Explain how the atmosphere affects the radiation from the Sun that reaches Earth’s surface, and how it affects the radiation leaving Earth. Then explain what happens to Earth’s average temperature if the amount of carbon dioxide in the atmosphere increases. [6]

11. (Higher Tier only) A table gives data for three satellites in circular orbits around the same planet.

Satellite	Orbit radius (m)	Time for one orbit (s)
P	6.8 × 10⁶	5580
Q	9.0 × 10⁶	8500
R	1.2 × 10⁷	13 100

(a) Calculate the speed of each satellite, to 3 significant figures. [3] (b) Describe the pattern in your results. [2] (c) Explain the pattern in terms of gravity, and state why satellite R cannot move at the speed of satellite P while staying at the same radius. [3]

12. (Higher Tier only) Three stars have the surface temperatures and strongest-emission wavelengths shown below.

Star	Surface temperature (K)	Wavelength of strongest emission (nm)
X	3500	828
Y	5800	500
Z	10 000	290

(a) Describe the relationship between temperature and the wavelength of strongest emission. [2] (b) A fourth star has a surface temperature of 8000 K. Predict whether its wavelength of strongest emission is greater than 500 nm, between 500 nm and 290 nm, or less than 290 nm. Give a reason. [1] (c) Star Z emits more energy per second from each square metre of its surface than star X. Name the property of the radiation that is greater, and say how the table supports this. [1]

Answers

1. The intensity (energy emitted per second per unit area) increases [1]. The wavelength at which the emission is strongest becomes shorter, so the distribution shifts to shorter wavelengths [1]. [2] Examiner insight: a statement such as “it gives out more radiation” is usually too vague to separate intensity from wavelength, so name both properties.

2. All bodies emit radiation, and at low temperature the bar emits infrared, which cannot be seen [1]. As the temperature rises the distribution moves to shorter wavelengths and the intensity rises, so red light is emitted and becomes visible [1]. At a higher temperature the emission includes yellow, green and blue wavelengths as well as red, so the glow looks yellow-white [1]. [3] Examiner insight: answers that say the bar “starts to give out radiation” when it glows lose credit, because the bar was emitting infrared all along.

3. Inner planets are rocky with a solid surface, while outer planets are gas giants or ice giants [1]. Inner planets are smaller and denser than outer planets [1]. Inner planets have few or no moons, while outer planets have many [1]. Other correct differences (ring systems, thick atmospheres) are also creditworthy, up to three marks. [3] Examiner insight: a comparison needs both sides, so “the outer planets are larger” earns its mark only because the contrast with the inner planets is clear from the question.

4. (a) Above the equator [1]. One orbit takes 24 hours, in the same direction as Earth spins, so it stays above the same point [1]. Another correct feature, such as a height of about 36 000 km above the surface, is also creditworthy, up to two marks. [2] (b) Use: mapping, monitoring the environment, weather or surveillance [1]. Reason: it passes over both poles at low height, and Earth turns beneath it, so over a day it covers the whole surface [1]. [2] Examiner insight: “geostationary means it does not move” is a common wrong statement. It moves at the same rate as Earth’s rotation.

5. Distance in one orbit = 2π × 7.4 × 10⁶ = 4.65 × 10⁷ m [1]. Speed = distance / time = 4.65 × 10⁷ / 6330 [1]. Speed = 7350 m/s [1]. [3] Examiner insight: using the radius as the distance travelled in one orbit is a frequent slip, and writing the unit with the final answer is part of a complete response.

6. Velocity has a direction as well as a speed [1]. The direction of the satellite is changing all the time, so its velocity changes [1]. A change in velocity is an acceleration, so a resultant force is needed [1]. The force is gravity, acting towards the centre of the orbit (at right angles to the motion) [1]. [4] Examiner insight: the strongest answers separate speed from velocity explicitly instead of saying the satellite “is not accelerating because it is not speeding up”.

7. (a) The closer satellite travels faster [1]. Gravity is stronger nearer to Earth, so a greater speed is needed to stay in a stable circular orbit instead of falling inwards [1]. [2] (b) The first satellite can no longer stay at the same radius [1]. A stable orbit at the higher speed needs a different radius, and a faster-moving satellite moves into a larger orbit where gravity is weaker [1]. [2] Examiner insight: keep the argument in terms of speed and radius being linked; a statement that “speed and radius are unrelated” contradicts the specification wording.

8. Net power = 320 − 250 = 70 W [1]. Time = 15 × 60 = 900 s [1]. Energy = 70 × 900 = 63 000 J [1]. [3] Examiner insight: a net gain needs the difference between absorbed and emitted power, and the time must be in seconds before multiplying.

9. The black surface absorbs more of the incoming radiation than the silver surface [1]. The silver surface reflects more of it [1]. So the net energy gained by the black tin is greater, and it warms more [1]. [3] Examiner insight: the argument must be about absorbed radiation. Saying “black attracts heat” gives no physics for a mark.

10. Some of the Sun’s radiation is reflected by clouds, or absorbed by the atmosphere, for example ozone absorbs ultraviolet [1]. The rest passes through, and is absorbed by the surface [1]. Earth’s surface is much cooler than the Sun and emits mainly infrared [1]. Greenhouse gases absorb some of the infrared and re-emit it in all directions, including back to the surface [1]. More carbon dioxide means less infrared escapes to space, so emitted radiation is less than absorbed [1]. Earth warms, emits more, and the balance is restored at a higher temperature [1]. [6] Examiner insight: the answer should stay with absorbed against emitted radiation, and it should end with equilibrium at a higher temperature rather than a temperature that rises for ever.

11. (a) Speed = 2πr / T. P: 2π × 6.8 × 10⁶ / 5580 = 7660 m/s [1]. Q: 2π × 9.0 × 10⁶ / 8500 = 6650 m/s [1]. R: 2π × 1.2 × 10⁷ / 13 100 = 5760 m/s [1]. [3] (b) As the orbit radius increases, the speed decreases [1]. The time for one orbit increases [1]. [2] (c) Gravity is weaker at a larger radius, so a smaller speed is enough for a stable orbit [1]. A stable orbit at the radius of R has one speed, which is lower than that of P, so at the speed of P the satellite could not stay at that radius [1]. Its radius would change to that of a larger orbit [1]. [3] Examiner insight: a data question wants the actual values used in the explanation, so refer to the speeds you calculated instead of general statements.

12. (a) As temperature increases, the wavelength of strongest emission gets shorter [1]. This holds across all three stars: 828 nm, 500 nm, 290 nm as temperature goes up [1]. [2] (b) Between 500 nm and 290 nm, because 8000 K lies between 5800 K and 10 000 K, and hotter means shorter wavelength [1]. [1] (c) Intensity is greater, because Z is hotter than X (10 000 K against 3500 K) [1]. [1] Examiner insight: in a prediction from a table, a reference to the neighbouring values is what makes the reason checkable.

Where marks are usually lost

• Describing speed as changing direction. Use velocity for the quantity that has direction.
• Forgetting to state the direction of the gravitational force on an orbiting body: towards the centre.
• Treating emission as something only hot objects do.
• Giving a vague “more radiation” instead of separate points on intensity and wavelength.
• Mixing up geostationary and polar orbits, or quoting the wrong period.
• Writing 2πr / T with the diameter in place of the radius, or forgetting to convert hours and minutes to seconds.
• Saying the greenhouse effect “traps heat” without naming infrared absorbed and re-emitted.
• Ending a temperature-balance answer before the new equilibrium is described.

Next steps

• Go back to the revision notes for the short summary.
• Re-read the study guide for the worked examples.
• Check progress on the OCR GCSE Physics hub and the printable checklist.
• Take the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OCR GCSE (9-1) Gateway Science Physics A (J249), Version 5.0 (July 2026), first assessment 2018, published by OCR.