Which of the following statements about diffraction is true?

• A. It does not involve interference
• B. It is not affected by aperture size
• C. It cannot occur in ultrasound
• D. It describes a pattern of maxima and minima produced by waves passing through a small aperture

Answer: (D)

Diffraction arises when waves encounter an opening or obstacle, and the different parts of the wavefront interfere with each other as they spread. This interference creates a pattern of alternating bright (maxima) and dark (minima) regions, not a single, sharp beam.

Because the pattern depends on how the wavefront is cut by the aperture, the size of the opening matters: a smaller opening relative to the wavelength causes the waves to spread more and produce a clearer set of fringes. This is why a diffraction pattern shows maxima and minima from waves passing through a small aperture.

Ultrasound waves, being waves too, can diffract, so the statement that diffraction cannot occur in ultrasound is false. Diffraction inherently involves interference, so a statement claiming no interference is false. The idea that the pattern is not affected by aperture size is also false.

The statement that best describes diffraction is that it describes a pattern of maxima and minima produced by waves passing through a small aperture.