A thin lens has a convex surface whose radius of curvature is 25.5 cm and a conc

Question

A thin lens has a convex surface whose radius of curvature is 25.5 cm and a concave surface whose radius of curvature is 47.0 cm. The index of refraction of the glass is 1.50.

a) draw a sketch of the lens

b) what is the focal length of the lens? Is the lens converging or diverging?

c) A real point object is located 30 cm from the lens. Where is the image?

d) Is the image real or virtual?

e) if you reverse the lens so the concave surface is the first surface, show that the lensmaker's equation gives the same result for the focal length.

Explanation / Answer

b) for a lenbs,

1/f= (u-1)*(1/R1 -1/R2)

or 1/f=(1.5-1)*(1/25.5 - 1/47)

or f=111.488 cm

b) using 1/u+1/v=1/f,

1/30 + 1/v=1/111.488

or v=-41.0445 cm

d)the image is virtual.

e)this can easily be stated by principle of revesibility of linght. if we consider the fact,

1/f=(1.5-1)*(-1/47 - (-1/25.5))

or f=111.588 cm

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