Question -
Answer -
Fresnel’s distance (ZF)is the distance for which the ray optics is a good approximation. It is givenby the relation,
Where,
Aperturewidth, a = 4 mm = 4 ×10−3 m
Wavelengthof light, λ = 400 nm = 400 × 10−9 m
Therefore, the distance for whichthe ray optics is a good approximation is 40 m.