|Class 12 Physics Wave Optics||Validity of wave optics|
Validity of wave optics
Problem: Estimate the distance for which ray optics is good approximation for an aperture of 4 mmand wavelength 400 nm.
Answer:- Fresnel’s distance (ZF) is the distance for which the ray optics is a good approximation. Itis given by the relation,
ZF = (a2/λ)
Aperture width, a = 4 mm = 4 ×10−3 m
Wavelength of light, λ = 400 nm = 400 × 10−9 m
ZF = (4x10-3)2/ (400x10-9)
Therefore, the distance for which the ray optics is a good approximation is 40 m.
Problem:- A slit 4cm wide is irradiated with microwaves of wavelength 2cm.Find the angular spread of central maximum, assuming incidence normal to the plane of the slit?
Answer:- Distance between the slits d=4cm,λ=2cm
The half angular speed of central maxima is given by,
d sinθ1 =1 x λ =λ
Therefore sinθ1 =(λ/d) = (2/4) =0.5
Or θ1 =300.