i)When you look at your face in a small bathroom mirror from a distance of 21 cm
ID: 1424645 • Letter: I
Question
i)When you look at your face in a small bathroom mirror from a distance of 21 cm, the upright image is twice as tall as your face. What is the focal length of the mirror? In cm
ii)A microscope has an objective lens with f = 16.22 mm and an eyepiece with f = 9.6 mm. With the length of the microscope's barrel set at 29.0 cm, the diameter of an erythrocyte's image subtends an angle of 14.3 mrad with the eye. If the final image distance is 28.5 cm from the eyepiece, what is the actual diameter of the erythrocyte? Hint: Start with the size of the final image then use the thin-lens formula for each lens to find their combined magnification. Use this magnification to calculate the object size in the final step. in µm
iii) The near point of a patient's eye is 76.2 cm.
(a) What should be the refractive power of a corrective lens prescribed to enable the patient to clearly see an object at 28.0 cm?
= value in dpt
(b) When using the new corrective glasses, the patient can see an object clearly at 30.4 cm but not at 28.0 cm. By how many diopters did the lens grinder miss the prescription?
value in dpt
Explanation / Answer
i)
do = object distance = 21 cm
m = magnification = 2
di =image distance
using the formula for magnification
di/do = m
di/21 = 2
di = 42 cm
Using the mirror equation
1/f = 1/di + 1/do
1/f = 1/42 + 1/21
f = 14 cm
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