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What is the approximate radius of the ce...

What is the approximate radius of the central bright differaction spot of light of wavelength `lambda=0.5 mum`, if focal length of the lens is 20 cm and radius of aperture of the lens is 5 cm ?

Text Solution

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`r_0=(0.61 lamda f)/a`
Putting values `r_0=(0.61 times 0.5 times 10^-8 times 20 times 10^-2)/(5 times 10^-2)`
`=1.22 times 10^-6 m`
=`1.22mu m`
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