An investigator shines a narrow-band ultraviolet laser ( ) normally onto two metal plates
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
An investigator shines a narrow-band ultraviolet laser (λ=400nm) normally onto two metal plates. Plate A has surface irregularities smaller than 50nm; Plate B has evenly spaced parallel grooves 500nm apart. Far-field intensity patterns are recorded for each plate.
Which observation would most strongly indicate that the ray model fails for Plate B but remains adequate for Plate A?
(a) Both plates reflect all incident light only at the specular angle predicted by geometric optics.
(b) Plate A shows uniform diffuse reflection, while Plate B reflects only at the specular angle.
(c) Plate B produces multiple bright maxima at specific angles while Plate A yields a single specularly reflected beam.
(d) Both plates produce several diffraction orders at discrete angles on either side of the normal.