CSEC PHYSICS / CLASS 12 · WAVE MOTION

Watch the waves bend.

Change the water depth. Follow the crests. Discover what changes—and what stays the same.

v = f λ

Speed = frequency × wavelength

Your ripple tank. One boundary. Plenty to discover.
THE RIPPLE TANK

A closer look at refraction

Top-down ripple tank: water-wave refractionCrests travel from region 1 to region 2. Incident angle 45.0 degrees; refracted angle 30.0 degrees, both measured from the normal. Speed 44.3 to 31.3 centimetres per second. Wavelength 44.3 to 31.3 centimetres. Frequency 1 hertz in both regions.REGION 1Deeper water · 2.0 cmREGION 2Shallower water · 1.0 cmNormali = 45.0°r = 30.0°λ₁ = 44.3 cmλ₂ = 31.3 cmDepth boundaryWave crestDirection of travelλ = crest spacing

Angles are measured from the normal. Direction arrows are perpendicular to the wave crests.

REGION 12.0 cm depth
Speed
44.3 cm/s
Wavelength
44.3 cm
Incidence angle
45.0°
REGION 21.0 cm depth
Speed
31.3 cm/s
Wavelength
31.3 cm
Refraction angle
30.0°
SAME SOURCE · BOTH REGIONS1.00 Hz

Frequency stays the same across the boundary.

What the waves are showing

Entering shallower water: waves slow down and have a shorter wavelength. Their direction bends towards the normal. Frequency stays the same across the boundary.

The physics behind the ripple tank

These are ideal, small-amplitude, long water waves: their wavelengths are much larger than either water depth. “Deeper” and “shallower” compare the two tank regions; both use the shallow-water approximation.

v = √(gh), with g = 9.81 m/s² and h in metres. λ = v/f. At the boundary, sin(r)/sin(i) = v₂/v₁ for nonzero incidence. At 0° both angles are zero. Each angle is measured from the normal, perpendicular to the boundary.

The floor changes height beneath a shared mean water level. Wavefront phase matches along the boundary. Wave amplitude is illustrative; partial reflection, amplitude changes, friction, surface tension and breaking are omitted. The shaded regions identify relative depth.

Changing a control immediately establishes a new steady wave pattern. This is a comparison of steady conditions, rather than a simulation of the transition between settings.

Model reference: MIT OpenCourseWare · Wave Propagation. Your settings and predictions reset when this page reloads.