OxfordAQA International GCSE Physics: Lenses, image formation and the eye (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 3.3.6, Lenses and the eye. The section is for the full Physics award and the course is untiered. If a topic feels shaky, go back to the study guide or the revision notes. The course hub and printable checklist are also available.

Questions

1. Terms for lenses.

(a) State what a convex lens does to parallel rays of light. [1] (b) State what a concave lens does to parallel rays of light. [1] (c) Define the focal length of a lens. [1]

2. A convex lens has a focal length of 10 cm. For each object distance, describe the image, saying whether it is real or virtual, upright or inverted, and larger or smaller than the object.

(a) The object is 30 cm from the lens. [2] (b) The object is 15 cm from the lens. [2] (c) The object is 6 cm from the lens. [2]

3. Magnification.

(a) An image is 4.5 cm tall and the object is 1.5 cm tall. Calculate the magnification. [2] (b) A lens has a magnification of 0.25 and the object is 6.0 mm tall. Calculate the height of the image. [2] (c) A microscope image of an insect hair is 18 mm long and the magnification is 12. Calculate the real length of the hair. [2]

4. A student draws a ray diagram on graph paper with 1 cm squares. The convex lens is a vertical line through x = 0 and the axis is y = 0. The focal length is 2 cm. The object is an arrow 2.0 cm tall with its foot at x = −6 cm on the axis.

(a) Describe the two rays you would draw from the tip of the arrow and where each goes. [3] (b) State the distance of the image from the lens and its height. [2] (c) Describe the nature of the image. [1]

5. A convex lens of focal length 6.0 cm is used as a magnifying glass to look at a stamp detail 1.5 mm tall. The detail is 4.0 cm from the lens.

(a) Explain why the lens acts as a magnifying glass at this distance. [1] (b) A ray diagram drawn on graph paper shows the image 12 cm from the lens, on the same side as the stamp. Describe the image. [3] (c) The image is 4.5 mm tall. Calculate the magnification. [2]

6. A concave lens has a focal length of 3.0 cm. An object 4.5 cm tall is placed 6.0 cm from it.

(a) Describe the image. [3] (b) A ray diagram shows that the image is 1.5 cm tall. Calculate the magnification. [2]

7. State the function of each part of the eye.

(a) Cornea [1] (b) Iris [1] (c) Lens [1] (d) Ciliary muscle [1] (e) Suspensory ligaments [1] (f) Retina [1]

8. A person looks up from a book to a tree on a distant hill. Explain how the eye changes so that the tree is in focus. [5]

9. A person has a near point of 80 cm.

(a) State whether a book held 30 cm from the eye can be seen clearly without glasses. [1] (b) Give two possible causes of this defect. [2] (c) Explain where the image forms without correction, and how a lens corrects the problem. [3]

10. A person’s near point is 25 cm and the far point is 2.0 m.

(a) State the usual position of the far point for a typical eye. [1] (b) Give one possible cause of this person’s defect. [1] (c) Explain why distant objects look blurred and how a lens corrects this. [3] (d) Calculate this person’s range of vision in centimetres. [1]

11. Lasers.

(a) Describe what is meant by a laser. [1] (b) Give two uses of lasers other than in the eye. [2] (c) State how lasers can be used in eye surgery. [1]

12. A camera and an eye both form images.

(a) Name the part of the eye that is equivalent to the CCD sensor in a camera. [1] (b) Compare how the camera and the eye change focus when looking from a distant object to a near object. [4] (c) A person 1.8 m tall is photographed. The image on the sensor is 12 mm tall. Calculate the magnification, giving your answer to 2 significant figures. [3]

Answers

1. (a) Rays are brought together (converge) at the principal focus [1]. (b) Rays spread out (diverge), as if they came from the principal focus [1]. (c) The length from the lens to the point where parallel rays meet (convex) or appear to start (concave) [1]. [3] Examiner insight: “Meet at a point” scores only if you say the rays were parallel to the axis, so keep that condition in your wording.

2. (a) The object is further than twice the focal length (20 cm). The image is real and inverted [1] and smaller [1]. (It is 15 cm from the lens and half the height.) (b) The object is between f and 2f. The image is real and inverted [1] and larger [1]. (It is 30 cm from the lens.) (c) The object is inside the principal focus. The image is virtual and upright [1] and larger [1]. [6] Examiner insight: Give all three features each time. An answer such as “real” without orientation or size usually leaves marks unclaimed.

3. (a) Magnification = 4.5 ÷ 1.5 [1] = 3.0 [1]. (b) Image height = 0.25 × 6.0 [1] = 1.5 mm [1]. (c) Object height = 18 ÷ 12 [1] = 1.5 mm [1]. [6] Examiner insight: Showing the rearranged equation or the substitution gives the examiner something to credit if your final number slips. Magnification is a ratio, so do not write a unit for it.

4. (a) Ray 1 goes from the tip parallel to the axis to the lens, then through the principal focus at (2, 0) on the far side [1]. Ray 2 goes from the tip through the centre of the lens at (0, 0) without bending [1]. The image tip is where they cross [1]. (b) Ray 1 runs from (0, 2) through (2, 0), and ray 2 runs from (−6, 2) through (0, 0). They cross at (3, −1) [1]. The image is 3 cm from the lens and 1.0 cm tall [1]. (c) Real, inverted and smaller (height 1.0 cm against 2.0 cm) [1]. [6] Examiner insight: On graph paper, draw with a ruler and extend the rays until they cross clearly. Read values from the squares, and give the position and the height as separate quantities.

5. (a) The stamp is closer to the lens than the principal focus (4.0 cm is less than 6.0 cm) [1]. (b) The image is virtual [1], upright [1] and larger than the object [1]. (c) Magnification = 4.5 ÷ 1.5 [1] = 3.0 [1]. [6] Examiner insight: Both heights are in millimetres here, so no conversion is needed. Using the lens-to-image distance instead of the heights is a common wrong route.

6. (a) The image is virtual [1], upright [1] and smaller than the object [1]. (It is on the same side as the object.) (b) Magnification = 1.5 ÷ 4.5 [1] = 0.33 [1]. [5] Examiner insight: Whatever the object distance, a concave lens gives the same type of image. Saying “real” for any case suggests the rays have been drawn crossing.

7. (a) Refracts light entering the eye [1]. (b) Controls the size of the pupil, and so how much light enters [1]. (c) Refracts the light and changes shape to focus it on the retina [1]. (d) Changes the shape of the lens [1]. (e) Connect the ciliary muscle to the lens and pull the lens thinner when the muscle relaxes [1]. (f) Contains light-sensitive cells where the image is focused [1]. [6] Examiner insight: Give a function with a verb, such as “refracts” or “controls”. Saying where a part is does not describe what it does.

8. The ciliary muscle relaxes [1]. The suspensory ligaments are pulled tight [1]. The lens is pulled thinner and less curved [1]. It refracts light less, so its focal length is longer [1]. Light from the distant tree is then focused on the retina [1]. [5] Examiner insight: An explanation of a change gains credit for a chain of linked statements. List muscle, ligaments, lens shape and effect in order.

9. (a) No, it cannot be seen clearly, because 30 cm is closer than the near point of 80 cm [1]. (b) Any two from: the eyeball is too short [1]; the eye lens is unable to focus a sharp image on the retina [1]. (c) Without correction the image of a near object forms behind the retina [1]. A convex lens is used [1]. It converges the rays slightly before they enter the eye, so the eye can focus them on the retina [1]. [6] Examiner insight: In part (b), two different causes are needed. Two wordings of one cause earn one mark at most.

10. (a) Infinity [1]. (b) The eyeball is too long, or the eye lens is unable to focus a sharp image on the retina [1]. (c) Light from distant objects focuses in front of the retina [1]. A concave lens is used [1]. It spreads the rays slightly before they enter the eye so that the image falls on the retina [1]. (d) Range = 200 − 25 [1] = 175 cm. [6] Examiner insight: The far point was given in metres but the answer is required in centimetres, so convert before subtracting. A bare number without a unit is risky.

11. (a) A concentrated source of light [1]. (b) Any two from cutting, cauterising and burning [1] [1]. (c) To correct visual defects [1]. [4] Examiner insight: Explaining how a laser produces light earns nothing here. Name the uses.

12. (a) The retina [1]. (b) The camera changes the distance between the lens and the sensor [1], moving the lens further away from the sensor for a nearer object [1]. The eye changes the shape of its lens [1], making it thicker and more curved for the nearer object [1]. (c) Convert: 12 mm = 0.012 m [1]. Magnification = 0.012 ÷ 1.8 [1] = 0.00667, so 6.7 × 10⁻³ [1]. [8] Examiner insight: Put the two heights in the same unit before dividing. An answer of 6.7 comes from a unit mismatch, so check that the size is sensible.

Where marks are usually lost

• Describing an image with fewer than three features.
• Treating every convex-lens image as real. Inside the principal focus it is virtual.
• Writing that the lens in the eye moves instead of changing shape.
• Mixing up which lens corrects long sight (convex) and short sight (concave).
• Describing the pupil as the part that focuses light, rather than as an opening whose size the iris changes.
• Forgetting to convert both heights to the same unit before finding magnification.
• Drawing ray 2 with a bend at the lens, instead of straight through the centre.

Next steps

• Review the revision notes
• Reread the study guide
• Visit the OxfordAQA IGCSE Physics hub
• Tick off the printable checklist
• Take the free 10-minute diagnostics
• Book a free trial class

Official syllabus

OxfordAQA International GCSE Physics (9203), for exams May/June 2018 onwards, Version 5.2, published by OxfordAQA. These questions follow section 3.3.6, Lenses and the eye.