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Date November 2019 Marks available 2 Reference code 19N.3.SL.TZ0.7
Level Standard level Paper Paper 3 Time zone 0 - no time zone
Command term Construct Question number 7 Adapted from N/A

Question

The diagram, drawn to scale, shows an object O placed in front of a converging mirror. The focal point of the mirror is labelled F.

A planar wavefront of white light, labelled A, is incident on a converging lens. Point P is on the surface of the lens and the principal axis. The blue component of the transmitted wavefront, labelled B, is passing through point P.

Construct a ray diagram in order to locate the position of the image formed by the mirror. Label the image I.

[2]
a(i).

Estimate the linear magnification of the image.

[1]
a(ii).

Describe two features of the image.

[1]
a(iii).

Sketch, on the diagram, the wavefront of red light passing through point P. Label this wavefront R.

[1]
b(i).

Explain chromatic aberration, with reference to your diagram in (b)(i).

[2]
b(ii).

An achromatic doublet reduces the effect of chromatic aberration. Describe an achromatic doublet.

[2]
b(iii).

Markscheme

correctly draws any 2 of the 4 conventional rays from the object tip ✔
correctly extends reflections to form virtual upright image I in approximate position shown ✔

NOTE: No ECF for incorrect rays in MP1.
Award [0] for rays of converging lens or diverging mirror.

a(i).

1.5 ✔

NOTE: For “correct” image position in (a)(i) allow 1.3 to 1.7

a(ii).

Any two of:
virtual OR upright OR larger than the object ✔

a(iii).

“circular” wave front through P: symmetric about the principal axis AND of greater radius than B ✔

b(i).

red and blue wave fronts have different curvature/radius
OR
red and blue waves are refracted differently/have different speeds ✔

so different colors have different foci/do not focus to one point
OR
so image is multi-coloured/blurred ✔

NOTE: MP1 is for the reason for the aberration, MP2 is for the effect.

b(ii).

mention combination of converging and diverging lenses ✔
of different refractive index/material ✔

NOTE: Achromatic doublet is in the question, so no marks for mentioning this.

b(iii).

Examiners report

[N/A]
a(i).
[N/A]
a(ii).
[N/A]
a(iii).
[N/A]
b(i).
[N/A]
b(ii).
[N/A]
b(iii).

Syllabus sections

Option C: Imaging » Option C: Imaging (Core topics) » C.1 – Introduction to imaging
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