A lensmaker wants to make a magnifying glass from glass with n = 1.55 and with a

Question

A lensmaker wants to make a magnifying glass from glass with n = 1.55 and with a focal length of 22.5 cm .

Part A

If the two surfaces of the lens are to have equal radii, what should that radius be?

Express your answer with the appropriate units.

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A lensmaker wants to make a magnifying glass from glass with n = 1.55 and with a focal length of 22.5 cm .

Part A

If the two surfaces of the lens are to have equal radii, what should that radius be?

Express your answer with the appropriate units.

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Explanation / Answer

1/f = (n-1) [1/R1 - 1/R2 ]

R1 = R2

but for concave surface R is positive and for convex surface its -ve

1/f = (n-1)[1/R -(-1/R)]

1/f = (n-1)[2/R]

put values n= 1.55 and f = 22.5 cm

1/22.5 = (1.55-1)(2/R)

R = 24.75 cm

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