O-LevelPhysicsLight5054/22 · Oct/Nov 2020 · Q815 Marks

A thin converging lens is made of a transparent material of refractive index 1.4.

(a)A ray of light travelling in air strikes the surface of the lens at an angle of incidence of 55°.
(a)(i)Calculate the angle of refraction. angle of refraction =[2]
(a)(ii)Place a tick (✔) in one of the boxes in the third column of Table 8.1 to indicate how the light ray deviates and what happens to the speed of the light in the ray as it enters the lens. [Table 8.1][1]
(a)(iii)State what happens to the frequency of the light in the ray as it enters the glass.[1]
(b)The focal length of the lens is 2.5cm.
(b)(i)State what is meant by focal length.[1]
(b)(ii)Fig. 8.1 is a full-scale diagram that shows an object O of height 3.0cm and the lens. [Figure 8.1 (full scale)] By drawing on Fig. 8.1, locate and mark the image I of O.[4]
(b)(iii)Determine the distance of I from the lens and calculate the magnification of O produced by the lens. distance = magnification =[3]
(c)Describe how a converging lens is used in a camera.[3]

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 2020). The mark or mark type is shown in brackets.

[1] (a)(i) n = sin i/ sin r or 1.4 = sin 55° / sin r or (r =) sin⁻¹(sin i/n) or (r =) sin⁻¹(sin 55°/ 1.4)
[1] (a)(i) 36°
[1] (a)(ii) towards (the normal) and speed decreases (i.e. fourth box only)
[1] (a)(ii) stays constant
[1] (a)(iii) distance between (one) focal point/principal focus and (the centre of) lens
[1] (b)(i) at least one correct focal point labelled / clear / used
[2] (b)(ii) any two from drawn: paraxial ray from tip of O to lens and refracted through correct far F ray from tip of O through optical centre and undeviated ray from tip of O through correct near F to lens and refracted paraxially
[1] (b)(ii) I marked at intersection of correct rays
[1] (b)(iii) 3.4 cm ≤ distance ≤ 3.5 cm
[1] (b)(iii) (magnification =) candidate's distance /9.0 or candidate's height/3.0
[1] (b)(iii) 0.37 ≤ magnification ≤ 0.40 c.a.o.
[3] (c) any three from: light (from subject/object) focussed / refracted by lens by moving/sliding/adjusting lens real image (of subject/object) formed on digital light detector/film

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