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Solutions: Medical Option - the EYE

Q4.

A lens is used as shown in the diagram to enable a person with an eye defect to see distant objects clearly.

(i) Name the defect corrected by this lens.

Short sight [myopia]

(ii) Determine the power of the lens.

u = infinity so 1/u = 0

v = - 0.50 m

P = 1/f = 1/u + 1/v

P = 0 - 1/0.50 = - 2.0 D (must be negative!)

(iii) Draw a ray diagram to show the path through the eye of rays from a distant object when a correcting lens is not being used.

Rays cross in front of retina from parallel incident rays

(iv) Draw a ray diagram to show the path through the eye of rays from an object positioned at the uncorrected far-point.

Image on retina, object at uncorrected far point

(Total 5 marks)