When two waves are superimposed on each other, the following occurrences are possible, except

Analyze the question: Superposition happens when two waves meet in the same region. We need to find the one option that does NOT result from superposition (the "except").

Explain the concept: When waves superimpose, their displacements add (the principle of superposition). This can produce:

• Interference: Constructive interference gives anti-nodal lines, where the waves reinforce each other. Destructive interference gives nodal lines, where the waves cancel each other.
• Stationary (standing) waves: Two waves of the same frequency and amplitude travelling in opposite directions superimpose to form a stationary wave.
• Dispersion: This is the separation of a wave into its component frequencies or wavelengths because the wave speed in a medium depends on frequency. An example is white light splitting into colours in a prism. It is caused by the medium's properties (refraction), not by superposition of two waves.

Check each option:

• A. Nodal lines: occur through destructive interference, so they are possible.
• B. Anti-nodal lines: occur through constructive interference, so they are possible.
• C. Stationary waves: formed by superposition of oppositely travelling waves, so they are possible.
• D. Dispersion: a property of a wave travelling through a medium, not a result of superposition, so it is not possible from superposition.

Answer: D. Dispersion.

Tip: Link superposition with the word "interference". Anything involving nodes, antinodes, beats, or standing waves comes from superposition. Dispersion, refraction, and diffraction belong to a wave's interaction with a medium or obstacle.