1.

a. Two lenses have power of (i) +2d (ii) -4D. What is the nature and focal length of each lens? b. An object is kept at a distance of 100 cm from lens of power -4D. Calculate the image distance.

Answer»

Solution :a. (i) CONVEX lens =+50 CM
(ii) CONCAVE lens =25 cm
b. `1/f=1/v-1/u`
`f=1/(-4D)=-25cm`
`u=-100cm`
`1/v=1/f+1/u`
`=-1/25-1/100`
`=(-5)/100=-1/20`
`v=-20cm`


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