The focal length of a convex lens is 16cm.
Where must be an object be placed so that the image formed by the lens is
a)real and twice as large
b)virtual and twice as large
lenses
2007-10-13 7:17 am
回答 (1)
2007-10-13 8:32 am
✔ 最佳答案
a) magnification m = 2 = v/ui.e. v = 2u
where u and v are the image and object distances respectively
since f = 16 cm
thus, using the thin lens formula
1/16 = 1/u + 1/v = 1/u + 1/2u
solve for u gives u = 24 cm
b) m = -2 = v/u
i.e. v = -2u
thus, 1/16 = 1/u - 1/2u
solve for u gives u = 8 cm
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