q1:For a normal eye, the focal length of the lens is f = 1.7 cm. If your friend

Question

q1:For a normal eye, the focal length of the lens is f = 1.7 cm. If your friend is farsighted such that the focal length of her lens is 2.0 cm, what should be the focal length of the corrective lens?the answer is 11.3 cm

how?

q2:Antireflective coatings on solar cells are often made by applying a thin film of silicon nitride (SiNx), which has an index of refractive of 1.2, on the top of the silicon solar cell, which has a refractive index of about 3.5. However, the sun emits radiation of various wavelengths which the solar cell absorbs, and the antireflective coating can only absolutely minimize the reflection of one of these wavelengths. The coating thickness is chosen to reduce the reflection of green/yellow light (E = 2.2 eV), which is the most intense color in the solar spectrum (shown below). Which of the following coatings would minimize reflection of green/yellow light?

answer is 820 nm how?

Explanation / Answer

we assume the lens are in contact

combined focal length

1/F = 1/f1 +1/f2

F = 1.7 required , f1 = 2.0 we use a diverign lens and f2 is -ve

1/f2 = 1/1.7 -1/2

f2 = 11.33 cm

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