Single-slit diffraction pattern

Steps:

• Waves passing through a gap of width a = λ diffract, with the central maximum spreading over angle θ ≈ λ / a for small angles.
• Initially, a = λ, so θ ≈ 1 radian (about 57°), defining the emergence angle.
• Widening the gap increases a while keeping incident wavelength λ constant.
• Larger a reduces θ (θ ≈ λ / a decreases), but λ of emerging waves stays the same as incident waves.

Why A is correct:

• Diffraction formula θ ≈ λ / a shows θ decreases as a increases; wavelength λ is unchanged by the gap.

Why the others are wrong:

• B: θ decreases, not increases; λ unchanged, not decreasing.
• C: θ decreases, not remaining same; λ unchanged, not increasing.
• D: θ decreases, not remaining same; λ unchanged, not decreasing.

Final answer: A