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Date May 2019 Marks available 2 Reference code 19M.3.SL.TZ2.11
Level Standard level Paper Paper 3 Time zone 2
Command term Determine Question number 11 Adapted from N/A

Question

A student places an object 5.0 cm from a converging lens of focal length 10.0 cm.

The student mounts the same lens on a ruler and light from a distant object is incident on the lens.

Construct rays, on the diagram, to locate the image of this object formed by the lens. Label this with the letter I.

[2]
ai.

Determine, by calculation, the linear magnification produced in the above diagram.

[2]
aii.

Suggest an application for the lens used in this way.

[1]
aiii.

Identify, with a vertical line, the position of the focussed image. Label the position I.

[1]
bi.

The image at I is the object for a second converging lens. This second lens forms a final image at infinity with an overall angular magnification for the two lens arrangement of 5. Calculate the distance between the two converging lenses.

[2]
bii.

A new object is placed a few meters to the left of the original lens. The student adjusts spacing of the lenses to form a virtual image at infinity of the new object. Outline, without calculation, the required change to the lens separation.

[2]
biii.

Markscheme

any two correct rays with extensions ✔

extensions converging to locate an upward virtual image labelled I with position within shaded region around focal point on diagram ✔

ai.

v = «–» 10«cm» ✔ 

M «= – v u =– – 10 5 » = «+» 2 ✔

 

 

aii.

magnifying glass

OR

Simple microscope

OR

eyepiece lens ✔

aiii.

I labelled at 25 cm mark ✔

bi.

the second lens has  f « = 10 5 » = 2  «cm» ✔

«so for telescope image to be at infinity»

the second lens is placed at 27 «cm»

OR

separation becomes 12 «cm» ✔

bii.

image formed by 10 cm lens is greater than 10 cm/further to the right of the first lens ✔

so second lens must also move to the right OR lens separation increases ✔

Award [1 max] for bald “separation increases”.

biii.

Examiners report

The simple ray diagram was constructed well by most candidates, especially compared to previous years.

ai.

The very simple calculation of magnification was done well by nearly everybody.

aii.

Using a converging lens as a magnifying glass was the most common correct answer.

aiii.

Another very easy and well answered ray diagram question.

bi.

Only candidates who realised that a simple telescope was being constructed were able to answer the question correctly. Most candidates realised that the focal lenses need to be added but few found the focal lens of the second lens correctly.

bii.

Many candidates did not read the question carefully and provided totally incorrect answers. It does not seem to be generally well known that if a distant object is moved to the right, for a converging lens, then the real image must also move to the right.

biii.

Syllabus sections

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