I. Refraction II. Interference III. Diffraction Which of the above properties are common to all waves?

Analyze the question: We need to find which of refraction, interference and diffraction are properties common to all waves (both mechanical waves like sound and water waves, and electromagnetic waves like light).

Concept: Every wave, whatever its type, shows these behaviours:

• Refraction: a change in direction (and speed) when the wave passes from one medium to another. Sound refracts, water waves refract, and light refracts.
• Interference: when two waves meet, they superpose and produce reinforcement or cancellation. This applies to all waves (beats in sound, bright and dark fringes in light).
• Diffraction: waves spread out when they pass through a gap or around an obstacle. This applies to all waves (you can hear someone around a corner, water waves bend through a harbour gap, and light bends around narrow slits).

Solution:

• I. Refraction: common to all waves ✔
• II. Interference: common to all waves ✔
• III. Diffraction: common to all waves ✔

So all three properties are shared by all waves. (Polarisation, by contrast, is NOT common to all waves because it occurs only in transverse waves. That is the property JAMB likes to use as a trap.)

Answer: Option B, I, II and III.

Exam tip: Remember the "RID" waves: Refraction, Interference, Diffraction (plus reflection) apply to ALL waves. Polarisation applies only to transverse waves. If a question mentions polarisation, it is a transverse-only property.