Question

A linear aperture whose width is 0.02 C is placed immediately in front of a lens e focal length 60 cm. The aperture is
illuminated normally by a parallel beam d wavelength 5 x 10^-5 cm. The distance of
the first dark band of the diffraction pattern from the centre of the screen is
​

Answer 1

Q}____?

=> 0.015 cm

Explanation:

Key idea Ist minima is formed at a distance

Y = λD/a

For the distance of the first dark band of the diffraction pattern from the centre of the screen is given by positon of Ist minima

i.e Y = λD/a

Where

λ = Wavelength of parallel beams

D = focal length

a = width of linear aperture

=>Y =[ ( 5× 10^-5 ) ( 0.6 ) ] / (0.02 × 10^-2

...[Given]

=>Y = 0. 15 cm

The Distance of First dark band of diffraction pattern from the centre of the screen is 0.15 cm !

Answer 2

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f=D=60 cm

For first minima,

y=aλD=2×10−2×10−25×10−7×60=0.15 cm