O-LevelPhysicsLight5054/21 · Oct/Nov 2025 · Q410 Marks

Fig. 4.1 shows a ray of light striking the left-hand surface of a thin glass converging lens. [Figure 4.1]

(a)Explain why the ray refracts and changes direction as it enters the glass.[2]
(b)(i)the principal focus (focal point) of a lens[2]
(b)(ii)the focal length of a lens.[1]
(c)(i)On Fig. 4.2, draw an arrow to represent the height and position of object O. The arrow should start on the principal axis.[1]
(c)(ii)On Fig. 4.2, draw two rays from the tip of the arrow drawn in (c)(i) to locate the position of the tip of the image I of object O. Draw an arrow to represent the image I of the object O. Label the image I.[3]
(c)(iii)State whether the image I of the object O is a real or a virtual image, and explain your answer.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[B2] any two from: (in glass) light/it travels more slowly/at a different speed; enters (an optically) denser medium/medium with different refractive index; wavelength changes (and frequency stays the same); angle of incidence is greater than 0
[C1] (point) where parallel rays meet (after refraction)
[A1] (point) where rays parallel to principal axis meet (after refraction) or (point) where paraxial rays meet (after refraction)
[B1] distance between principal focus/focal point and (centre of) lens
[B1] arrow of height 1.8 cm and 2.2 cm and on left of the centre of the lens
[M2] any two from: paraxial ray from tip of O to lens and from lens to F2; straight ray through centre of lens; ray that seems to come from F1 from tip of O to lens and emerges paraxially from lens
[A1] two rays traced back to image (labelled I)
[B1] virtual and rays (merely) seem to come from I/do not pass through the image / object distance less than focal length/the image is upright

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