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Question 18N.3.SL.TZ0.9

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Date November 2018 Marks available [Maximum mark: 7] Reference code 18N.3.SL.TZ0.9
Level SL Paper 3 Time zone TZ0
Command term Calculate, Determine, Draw Question number 9 Adapted from N/A
9.
[Maximum mark: 7]
18N.3.SL.TZ0.9

The diagram shows two light rays that form an intermediate image by the objective lens of an optical compound microscope. These rays are incident on the eyepiece lens. The focal points of the two lenses are marked.

(a)

Draw rays on the diagram to show the formation of the final image.

[2]

Markscheme

proper construction lines ✔

image at intersection of proper construction lines ✔

 

The object O is placed at a distance of 24.0 mm from the objective lens and the final image is formed at a distance 240 mm from the eyepiece lens. The focal length of the objective lens is 20.0 mm and that of the eyepiece lens is 60.0 mm. The near point of the observer is at a distance of 240 mm from the eyepiece lens.

(b.i)

Calculate the distance between the lenses.

[3]

Markscheme

distance of intermediate image from objective is 

1 v = 1 20 − 1 24 ie: v = 120 «mm» ✔

distance of intermediate image from eyepiece is

1 u = 1 60 − ( − 1 240 )  ie: u = 48 «mm» ✔

lens separation 168 «mm» ✔

(b.ii)

Determine the magnification of the microscope.

[2]

Markscheme

ALTERNATIVE 1:

eyepiece: m =  − v u = 240 28 = 5 ✔

AND

objective m =  − v u = − 120 24 = −5 ✔

Total m = −5 × 5 = −25 ✔

 

ALTERNATIVE 2:

m =  ( 240 60 + 1 ) × ( − 120 24 )  ✔

m = −25 ✔

 

Accept positive or negative values throughout.

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