Diffraction gratings reveal wavelength via interference patterns

Steps:

• Shine light through a diffraction grating with closely spaced slits.
• Observe the resulting diffraction pattern of bright and dark fringes on a screen.
• Measure the angles of the bright fringes from the central maximum.
• Apply the grating equation to calculate wavelength from slit spacing and angles.

Why D is correct:

• The diffraction grating equation, d sinθ = mλ, directly relates measurable angles (θ) and slit spacing (d) to wavelength (λ), allowing precise determination.

Why the others are wrong:

• A: Amplitude affects brightness but not fringe positions in diffraction.
• B: Intensity relates to overall light power, not pattern spacing.
• C: Speed is constant in a medium and unrelated to diffraction angles.

Final answer: D