Light of wavelength `5 xx 10^(-7)m` is diffracted by an aperture of width `2 xx 10^(-3)m`. For what distance travelled by the diffrated beam does the spreading due to diffraction become greater than width of the aperture ?

Explanation

The distance travelled by the diffracted beam will be equivalent to the Fresnel distance The Fresnel distance: The Fresnel distance is given by the relation
`z_(1)=(a^(2))/(lambda)`Substituting the values of a and, `lambda`we have
`z_(1)=((2xx10^(-3)m)^(2))/(5xx10^(-7)m)` =`( 4xx10^(-6))/(5xx10^(-7))(m^(2))/( m^(2))=8 m`