29. The radius of curvature of a plano-convex lens
which has 2 refractive index is 20 cm. By
applying Silver Bromide on its surface to
change it as a concave mirror, what is the focal
length of the formed mirror ?
(1) 20 cm
(2) 40 cm
(3) 5 cm
(4)10cm
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ANSWER :
The answer to your question is 5 cm.
To find out, use lens makers formula and then silvering of lens formula
LENS MAKERS FORMULA : 1/F= (μ-1)(1/R₁-1/R₂)
SILVERING OF LENS : 1/F= -2/f₁ + 1/f₂
where F= FOCAL LENGTH OF EQUIVALENT MIRROR
f₁ = focal length of lens
f₂ = focal length of mirror
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