Ripple Tank

What you will investigate

This virtual ripple tank lab uses water waves to connect a visible pattern with measured frequency, wavelength, direction, and path difference. Generate straight waves, reflect them from a barrier, pass them over a shallow region, send them through an opening, or combine two sources. The same water surface provides several investigations, but each comparison needs its own controlled variables. A change in source frequency is different from a change in water depth or opening width.

Make predictions before testing refraction, diffraction, and interference. Record the actual frequency from the counter and use a ruler to measure several wavelengths together. Dividing a five-wavelength span by five reduces the effect of reading a single short gap. The course's Real mode also distinguishes the motor dial from the measured frequency. A number on a control is a setting; the counter supplies the measurement used in your calculation.

Relating frequency, wavelength, and speed

The central relationship is v = fλ. The ideal model includes water-depth and surface-tension effects rather than assuming that water-wave speed is perfectly constant at every frequency. At a fixed depth, compare how wavelength changes when frequency changes. Then use the frequency and wavelength together to calculate speed, with wavelength expressed in meters when speed is required in meters per second.

Ideal setup	Frequency	Model wavelength	Model phase speed
Deep region, 5 mm	6 Hz	0.03666584551 m	0.2199950731 m/s
Deep region, 5 mm	10 Hz	0.02215888918 m	0.2215888918 m/s
Shallow region, 1.5 mm	10 Hz	0.01658174815 m	0.1658174815 m/s

These reference values come from the ideal model's validation table. Student ruler readings are rounded separately. At 10 Hz, the displayed wavelength comparison for the two depths is 22.2 mm versus 16.6 mm. Do not expect a calculation from rounded ruler readings to reproduce every digit of the continuous model value.

Refraction and reflection

In the depth comparison, the two regions share the same wave frequency while their wavelengths and speeds differ. At a 30° incident angle, the ideal refraction angle in the shallow region is approximately 21.972°, displayed as 22°. Measure angles relative to the normal, then explain the change using speed and wavelength. Frequency is set by the source and does not change merely because a wave crosses this boundary.

The reflection investigation checks a different relationship: reflected and incident angles are equal. Compare several angles instead of deciding from one picture. The surface before a reflecting barrier contains overlapping incident and reflected waves, so separate the directions from the combined instantaneous pattern. Water is not carried across the tank with each advancing crest; the cork illustration distinguishes local water motion from energy transfer.

Openings and two-source interference

For diffraction, compare opening widths at the same frequency. A narrow opening produces a wider spreading pattern in this investigation. The course measures a spreading angle on a defined scanning arc. At 10 Hz, openings of 1, 2, and 4 cm give displayed half-amplitude angles of 32°, 17°, and 9°. That angle describes spreading at the measurement arc; it is not a direct measurement of total transmitted energy.

With two sources, identify relatively still regions and more strongly moving regions. Measure distances to both sources and calculate their difference. On the first still line, compare the path difference with approximately half a wavelength. Use wavelength measured under matching conditions, especially in Real mode. Combining records from different settings can create an apparent disagreement that is actually a mismatch in the comparison.

Standards, limits, and teaching use

The learning goals connect to NGSS HS-PS4-1 and HS-PS4-3, New York wave topics, and AP Physics 2 wave relationships. The course supports algebraic reasoning with v = fλ and evidence for interference and diffraction. It does not claim to teach every wave topic: polarization, beats, and the quantitative optical single-slit treatment are outside this investigation.

Ask students to compare a claim, their recorded measurements, and a wave explanation. Repeat a controlled pair in Real mode to discuss ruler, angle, probe, and motor-setting errors. The numerical model and particle illustration simplify a physical tank; they are tools for investigating the stated relationships. Continue with flame tests and atomic spectra to connect wavelength with another observable phenomenon.