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Date May 2017 Marks available 2 Reference code 17M.3.SL.TZ2.8
Level Standard level Paper Paper 3 Time zone 2
Command term Determine Question number 8 Adapted from N/A

Question

The diagram shows planar wavefronts incident on a converging lens. The focal point of the lens is marked with the letter F.

M17/4/PHYSI/SP3/ENG/TZ2/08

Wavefront X is incomplete. Point Q and point P lie on the surface of the lens and the principal axis.

On the diagram, sketch the part of wavefront X that is inside the lens.

[1]
a.i.

On the diagram, sketch the wavefront in air that passes through point P. Label this wavefront Y.

[1]
a.ii.

Explain your sketch in (a)(i).

[2]
b.

Two parallel rays are incident on a system consisting of a diverging lens of focal length 4.0 cm and a converging lens of focal length 12 cm.

The rays emerge parallel from the converging lens. Determine the distance between the two lenses.

[2]
c.

Markscheme

line of correct curvature as shown

[1 mark]

a.i.

line of approximately correct curvature as shown

 

Judged by eye.

Allow second wavefront Y, to have “passed” P as this is how this question is being interpreted by some.

Ignore any waves beyond Y.

[1 mark]

a.ii.

wave travels slower in glass than in air
OR
RI greater for glass

wavelength less in glass than air

hence wave from Q will cover a shorter distance «than in air» causing the curvature shown

 

OWTTE

[2 marks]

b.

realization that the two lenses must have a common focal point

distance is 12 – 4.0 = 8.0 «cm»

 

Accept MP1 from a separate diagram or a sketch on the original diagram.

A valid reason from MP1 is expected.

Award [1 max] for a bald answer of 12 – 4 = 8 «cm».

[2 marks]

c.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.
[N/A]
c.

Syllabus sections

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

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