1.

A biconvex lens (n = 1.5) has a radius of curvature of magnitude 20 cm. Which one of the following options describe best the image formed of an object of height 2 cm place 30 cm from the lens?

Answer»

real, inverted, height = 1cm
virtual, UPRIGHT, height = 1 cm
virtual, upright, height = 0.5 cm
real, inverted, height = 4 cm

Solution :For the LENS `n=1.5 and |R_(1)|=|R_(2)|=20cm`. As per sign CONVENTION `R_(1)` is `+ve `but `R_(2)` is `-ve`.
`therefore""(1)/(f)=(n-1)((1)/(R_(1))-(1)/(R_(2)))=(1.5-1)((1)/(20)-(1)/((-20)))=(1)/(20) rArr f=+20 cm`
Now `u=-30 cm and H=2cm`
`therefore""(1)/(V)=(1)/(u)+(1)/(f)=(1)/((-30))+(1)/(20)=(1)/(60) rArr v=60cm and h.=(v)/(u)xxh=(60xx2)/((-30))=-4cm`
Thus, theimage is real, inverted and of height 4 cm.


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