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Date November 2020 Marks available 2 Reference code 20N.3.SL.TZ0.11
Level Standard level Paper Paper 3 Time zone 0 - no time zone
Command term Draw Question number 11 Adapted from N/A

Question

A beam of monochromatic light from infinity is incident on a converging lens A. The diagram shows three wavefronts of the light and the focal point f of the lens.

Draw on the diagram the three wavefronts after they have passed through the lens.

[2]
a.

Lens A has a focal length of 4.00cm. An object is placed 4.50cm to the left of A. Show by calculation that a screen should be placed about 0.4m from A to display a focused image.

[2]
b.

The screen is removed and the image is used as the object for a second diverging lens B, to form a final image. Lens B has a focal length of 2.00cm and the final real image is 8.00cm from the lens. Calculate the distance between lens A and lens B.

[3]
c.

Calculate the total magnification of the object by the lens combination.

[2]
d.

Markscheme

wavefront separation identical and equal to separation before the lens

wavefronts converging, approximately centered on f

 

By eye.

Dotted construction lines are not required, allow wavefronts to extend beyond or be inside the dotted lines here.

Allow [1 max] if only two wavefronts drawn. 

a.

1v=14.00-14.50 ✓

v=36.0 «cm» ✓

 

b.

A:1-2.0=18+1u ✓

u=-1.6 «cm»  ✓

distance necessary = «36.0-1.6=»34.4 «cm»

 

Allow [2 max] for ECF for no negative in MP1. Gives u=2.7 and distance of 38.7«cm»

Allow ECF from (b) in MP3.EG use of 0.4m/40cm.

c.

«m=-io=-364.5  for A or -8-1.6 for B»

mA=«»8  OR  mB=«+»5 ✓

total magnification =«» 40 ✓

 

Allow [2] marks for a bald correct answer

Allow ECF from (b) and (c).

Eg if u=2.7cm in (c) then mB=3 and total m=24

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.

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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