Calculate the focal length ofa reading glass of a person if his distance of ditinct visionis 75cm
Answer (1)
15th Apr, 2025
To calculate the focal length of a reading glass (convex lens), we can use the lens formula:
1/f = 1/v - 1/u
Given:
v = -75 cm (distance of distinct vision, negative because it's on the same side as the object)
u = -25 cm (normal near point, assume)
However, since the normal near point is not given, we'll use the formula for a simple magnifier:
f = D / (D/d - 1)
where D = 25 cm (normal near point) and d = 75 cm (distance of distinct vision)
f = 25 / (75/25 - 1)
f = 25 / (3 - 1)
f = 25 / 2
f = 37.5 cm
The focal length of the reading glass is 37.5 cm.
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