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A double convex lens made of glass of re...

A double convex lens made of glass of refractive index 1.5 has both radii of curvature 20 cm each. Find the focal length of the lens. If an object is placed at a distance of 15 cm from this lens, find the position of the image formed.

Text Solution

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`1/f = (n_(21) - 1) ((1)/(R_1) - (1)/(R_2))`
` = (1.5 -1) ((1)/(20) - (1)/(-20)) = 1/20`
or f = 20cm
Using ` 1/v - (1)/(-u) = 1/f ` , we get
` 1/v - (1)/(-15) = 1/20`
`v = -60 cm ` (on object side )
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