OCR GCSE Physics A: Reflection, refraction, lenses and colour (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 (J249) specification, Version 5.0 (July 2026), topic P5.3 Wave interactions. Questions 1, 2, 3 and 12 cover statements on both tiers. Questions marked (Higher Tier only) cover P5.3c, P5.3d or P5.3e. Where needed, use a speed of light in air of 3.00 × 10⁸ m/s. Describe ray diagrams in words or sketch them on paper.

Links: OCR GCSE Physics hub, printable checklist, study guide, revision notes, free diagnostics.

Questions

1. State three things that can happen to an electromagnetic wave when it meets a boundary between two substances. [3]

2. A red laser emits light of wavelength 633 nm in air. In a clear plastic the wavelength is 422 nm.

(a) Calculate the frequency of the light in air. [2] (b) Explain why the same frequency is used to find the speed in the plastic, then calculate that speed. [3]

3. Explain, in terms of wave speed, why a ray of light bends towards the normal when it passes from air into glass at an angle. [5]

4. (Higher Tier only) A ray of light hits a plane mirror at an angle of incidence of 35°.

(a) State the angle of reflection and the angle between the reflected ray and the mirror surface. [2] (b) A ray enters a rectangular glass block from air at an angle to the normal. Describe how to draw its path through the block and out of the other side. [3]

5. (Higher Tier only) An object stands on the axis of a convex lens, further from the lens than twice the focal length. Describe how to draw the image of the top of the object, and state the nature of the image. [4]

6. (Higher Tier only) A convex lens is used as a magnifying glass. Explain how it forms an image of a small object and state what kind of image it is. [3]

7. (Higher Tier only) Compare convex and concave lenses by stating one similarity and three differences in how they affect light. [4]

8. (Higher Tier only) A short-sighted person sees distant objects as blurred because the rays focus in front of the retina. Explain which type of lens corrects this. [3]

9. (Higher Tier only) A red book is lit by white light.

(a) Explain why it looks red. [2] (b) Explain what you would see if it were lit by green light only. [2]

10. (Higher Tier only) White light passes through a magenta filter, then through a green filter. Describe and explain what emerges. [4]

11. (Higher Tier only) You can read a page of white paper from many positions, but you only see a clear image of a window in a mirror from certain positions. Explain the difference. [5]

12. A pulse of light crosses a glass slab of thickness 0.60 m. Its speed in the glass is 2.0 × 10⁸ m/s. In the glass its wavelength is 350 nm.

(a) Calculate the time taken to cross the slab. [2] (b) Calculate how much longer this is than the time to travel 0.60 m in air. [2] (c) Calculate the frequency of the light. [2] (d) Calculate the wavelength of the light in air. [2]

Answers

1. Any three from: absorbed [1]; transmitted [1]; reflected [1]; refracted (not counted beyond three). [3] Examiner insight: Three separate, correct terms earn credit. Repeating one idea in different words, such as “bounced” and “reflected”, does not give a second point.

2. (a) f = v ÷ λ = 3.00 × 10⁸ ÷ 633 × 10⁻⁹ [1] = 4.74 × 10¹⁴ Hz [1] (b) Frequency is fixed by the source and does not change when light enters a new substance [1]. v = f λ = 4.74 × 10¹⁴ × 422 × 10⁻⁹ [1] = 2.00 × 10⁸ m/s [1] [5] Examiner insight: Answers that convert nanometres to metres at the start are easier to follow and easier to credit. An answer out by a power of ten shows the conversion step was missed.

3. Light travels more slowly in glass than in air [1]. The frequency stays the same, so the wavelength is shorter in the glass [1]. When the wave meets the boundary at an angle, one end of each wavefront enters the glass first [1] and slows down while the other end is still moving faster in the air [1]. This turns the wavefront, so the ray bends towards the normal [1]. [5] Examiner insight: Strong answers link the change of direction to the change of speed. Saying only “glass is denser” gives a reason without the mechanism the question asks for.

4. (a) The angle of reflection is 35° [1]. The angle to the mirror surface is 90° − 35° = 55° [1] (b) On entering the block the ray bends towards the normal [1]. On leaving the other side it bends away from the normal [1]. The emerging ray is parallel to the original ray but shifted sideways [1] [5] Examiner insight: Angles in reflection are measured from the normal. A diagram or description that uses the surface as the reference line is likely to lose the angle point.

5. Draw a ray from the top of the object parallel to the axis, bending through the principal focus on the far side [1]. Draw a second ray from the top through the centre of the lens, going straight on [1]. The point where the two rays cross is the top of the image [1]. The image is real, inverted and smaller, between F and 2F on the far side [1]. [4] Examiner insight: Use a ruler and put arrows on rays. A description of the image needs at least three properties: real or virtual, upright or inverted, and size.

6. The object is closer to the lens than the principal focus [1]. The rays leaving the lens spread out, so they do not meet, but trace back to appear to come from a point behind the object [1]. The image is virtual, upright and larger [1]. [3] Examiner insight: Say that the rays only appear to come from the image. A response that says the rays “meet” describes a real image instead.

7. Similarity: both refract light at their two surfaces (or both have a principal focus) [1]. Differences: a convex lens brings parallel rays together whereas a concave lens spreads them apart [1]; a convex lens can form a real image on a screen whereas a concave lens cannot [1]; a convex lens is thicker in the middle whereas a concave lens is thinner in the middle [1] [4] Examiner insight: A comparison needs both lenses in each statement. Writing “convex converges” alone does not state the contrast.

8. A concave lens [1]. The eye focuses the rays too soon, in front of the retina, so the rays need to be spread out slightly before they enter the eye [1]. The concave lens diverges the rays, so the focus moves back onto the retina [1]. [3] Examiner insight: Naming the correct lens is not enough. The explanation needs to say where the image forms and how the lens changes that.

9. (a) White light contains all the visible colours [1]. The book reflects red light and absorbs the other colours, so only red reaches the eye [1] (b) Green light contains no red to reflect [1]. The book absorbs the green light, so almost no light reaches the eye and it looks black [1] [4] Examiner insight: Say what the object absorbs as well as what it reflects. “It reflects red” alone is incomplete as an explanation of what happens under different light.

10. Magenta transmits red and blue and absorbs green [1]. The green filter only transmits green light [1]. No green light reaches the second filter because the first absorbed it [1]. No light emerges, so it looks black [1]. [4] Examiner insight: Treat each filter in turn and list what is left after each one. Answers that say the filters “mix” their colours miss that filters subtract.

11. Paper has a rough surface [1] which scatters light in many directions [1]. A mirror has a smooth surface [1] and gives specular reflection, where parallel rays stay parallel [1]. The reflected beam only reaches the eye from certain positions, so the image can only be seen from those positions [1]. [5] Examiner insight: The key term pair is rough versus smooth. Mention what happens to the reflected rays, not only the name of the process.

12. (a) t = d ÷ v = 0.60 ÷ 2.0 × 10⁸ [1] = 3.0 × 10⁻⁹ s [1] (b) Time in air = 0.60 ÷ 3.00 × 10⁸ = 2.0 × 10⁻⁹ s [1]. Difference = 3.0 × 10⁻⁹ − 2.0 × 10⁻⁹ = 1.0 × 10⁻⁹ s [1] (c) f = v ÷ λ = 2.0 × 10⁸ ÷ 350 × 10⁻⁹ [1] = 5.7 × 10¹⁴ Hz [1] (d) λ = 3.00 × 10⁸ ÷ 5.71 × 10¹⁴ [1] = 5.25 × 10⁻⁷ m (525 nm) [1] [8] Examiner insight: In a chain of calculations, work with unrounded values from earlier parts and round at the end. Show the substitution in each part so a slip can be traced.

Where marks are usually lost

• Taking angles from the mirror or block surface rather than from the normal.
• Saying frequency changes at a boundary when only the speed and wavelength change.
• Writing the cause of refraction as “density” with no mention of wave speed.
• Leaving wavelengths in nanometres in v = f λ.
• Describing a virtual image as one where the rays “meet”.
• Stating which lens corrects a fault without explaining where the image forms.
• Saying a filter “makes” light a colour rather than absorbing the other colours.
• Explaining an object’s colour from reflection only, without saying what it absorbs.

Next steps

• Review the revision notes and the study guide.
• Visit the OCR GCSE Physics hub and the printable checklist.
• Take one of 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. Topic P5.3 Wave interactions.