A convex lens of diameter 8.0 cm is used to focus a parallel bam of light of wavelength 620 nm. If the light be focused at a distance of 20 cm from the lens, what would be th eradius of the central bright spot formed?

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Solution

$λ = 620 n m = 620 \times 10^{- 9} m, D = 20 c m = 20 \times 10^{- 2} m, d = 8 c m = 8 \times 10^{- 2} m ∴ R = 1.22 \times \frac{620 \times 10^{- 9} \times 20 \times 10^{- 2}}{8 \times 10^{- 2}} = 1891 \times 10^{- 9} = 1.9 \times 10^{- 6} m$
So, Diameter $= 2 R = 3.8 \times 10^{- 6}$

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A convex lens of diameter 8.0 cm is used to focus a parallel bam of light of wavelength 620 nm. If the light be focused at a distance of 20 cm from the lens, what would be th eradius of the central bright spot formed?

λ=620nm=620×10−9m,D=20cm=20×10−2m,d=8cm=8×10−2m∴R=1.22×620×10−9×20×10−28×10−2=1891×10−9=1.9×10−6m So, Diameter =2R=3.8×10−6

$λ = 620 n m = 620 \times 10^{- 9} m, D = 20 c m = 20 \times 10^{- 2} m, d = 8 c m = 8 \times 10^{- 2} m ∴ R = 1.22 \times \frac{620 \times 10^{- 9} \times 20 \times 10^{- 2}}{8 \times 10^{- 2}} = 1891 \times 10^{- 9} = 1.9 \times 10^{- 6} m$
So, Diameter $= 2 R = 3.8 \times 10^{- 6}$