Question

A linear aperture whose width is 0.02 cm us placed immediately in front of a lens of focal length 60 cm

Answer 1

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



f= D = 60cm

for first minima

y = wavelength * D / a

y = 5 x 10-5 * 60 / 0.02 = 0.15 cm

Answer 2

The distance of the first dark band of the diffraction pattern from the center of the screen is

y = 0.15 cm

Explanation:

Focal length "f" = D =  60 cm  

Beam of wavelength " λ" = 5 x 10⁻⁵ cm

For first minima:

y = λD / a = 5 × 10^−7 × 60 / 2 × 10^−2 × 10−2

y = 5 × 10^−3 x 60 / 2

y = 0.15 cm

So the distance was 0.15 cm