The optical prescription for a pair of spectacles is :Right eye : −3.50 D Left eye : −4.00 D(a) Are these lenses thinner at the middle or at the edges?(b) Which lens has a greater focal length?(c) Which is the weaker eye?

 (a) These lenses are thinner at the middle because they have negative power which implies that they are a concave lens. 

(b) Lens for the right eye has greater focal length because power is inversely proportional to focal length $(P=\frac {1}{f})$. Therefore, a lens of lower power has a greater focal length which is -3.50D in this case.

(c) Left eye is the weaker eye because it needs a lens of greater power for its correction, which is -4D in this case.

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Updated on: 10-Oct-2022

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