Solutions: Medical Option - the EYE
Q5.
A defective eye has an unaided far point of 2.5 m and an unaided near point of 0.20 m. A correcting lens is used to produce an aided far point at infinity.
(a)
(i) Name the defect of vision affecting the eye.
Myopia ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) State one possible cause of this defect of vision.
The eyeball is too long or the cornea is too curved/powerful. ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(2 marks)
(b) Complete the three ray diagrams on below for the defective eye.
![](ediagram5ANS.png)
1st diagram: rays focused on retina ![](../../../../graphics/symbols/nuclides/ticksmall.png)
2nd diagram: rays focussed before retina ![](../../../../graphics/symbols/nuclides/ticksmall.png)
3rd diagram: symbol for the concave (diverging) lens,
rays diverging from lens,
rays (after diverging) focused on retina ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(5 marks)
(c)
(i) Calculate the power of the correcting lens.
u = infinity so 1/u = 0
v = - 2.5 m
P = 1/v + 1/u
= - 1/2.5 + 0
= - 0.4 D ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) Calculate the aided near point when wearing the correcting lens.
v = - 0.20 m
P = 1/v + 1/u
- 0.40 = 1/u - 1/0.20 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
1/u = 1/0.20 - 0.40 = 4.6
u = 0.22 m ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(4 marks)
(Total 11 marks)