Geometrical OpticsHard

Question

A biconvex lens has a radius of curvautre of magnitude 20 cm. Which one of the followingoption describe best the image formed of an objected of height 2 cm placed 30 cm fromthe lens?

Options

A.Virtual, upright height = 1 cm
B.Virtual, upright height = 0.5 cm
C.Real, inverted, height = 4 cm
D.Real, inverted, height = 1 cm

Solution

      
Let μ =
According to lens marker′s formula

For biconvex lens, R1 = + 20 cm, R2 = - 20 cm
∴          or f = 20 cm
According to thin lens formula
     
Here, u = - 30 cm
∴           
      v = 60 cm
The image is formed at a distance of 60 cm on the right hand side of the lense. It is a real image.
Magnification, m =
              ⇒ h1 = - 4 cm
-ve sign shows that image is inverted.
The image is real, inverted and height of 4 cm as shown in figure
Note : In this question the value of refrective index is not given.

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