1.

Find the power of a convex lens which forms a real, and inverted image of magnification -1 of an object placed at a distance of 20 cm from its optical centre.

Answer»

Solution :Here u = - 20 CM and MAGNIFICATION m = -1 for real and inverted image
`because""m = (v)/(u)`, hence `v = "MU" = (-1) xx (-20) = + 20` cm
`THEREFORE""(1)/(f) = (1)/(v) - (1)/(u) = (1)/((+20)) - (1)/((-20)) = (1)/(20) + (1)/(20) = (1)/(10)`
`rArr` f = 10 cm = 0.1 m
`therefore` Power of convex lens `P = (1)/(f("in m")) = (1)/(0.1 m) = + 10 D`


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