Which of the following characteristics of waves can a ripple tank be used to demonstrate? I. Reflection II. Refraction III. Diffraction

Analyze the question: A ripple tank is a shallow glass tank of water used to show how water waves behave. The question asks which wave characteristics it can demonstrate: reflection, refraction and diffraction.

Explain the concept: A ripple tank uses a vibrating dipper (or a straight bar) to produce plane or circular water waves. A lamp above the tank projects the wave pattern onto a screen below, so you can see what the waves are doing.

Show the solution:

• I. Reflection: Place a barrier in the path of the plane waves. The waves bounce off it, and the angle of incidence equals the angle of reflection. ✔
• II. Refraction: Place a glass plate in the tank to make a shallow region. The waves travel more slowly there, so their wavelength shortens and their direction changes. ✔
• III. Diffraction: Make a gap in the barrier. The waves spread out as they pass through, and the spreading is greatest when the gap is about the size of the wavelength. ✔

The ripple tank demonstrates all three, and it can also show interference.

Identify the answer: I, II and III, which is option A.

Option B is a misprint ("II and II only") and does not make sense. Options C and D leave out one of the three behaviours, which the tank can in fact show.

Tip: Remember "RRDI": Reflection, Refraction, Diffraction, Interference. A ripple tank shows all four, so when a WASSCE or JAMB question asks about ripple tank demonstrations, "all of the above" is usually correct.