Describe ripple tank refraction across a depth change
Use a shallow region to compare transmitted spacing and direction while retaining the source cycle rate.
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028, section 3.1. Core covers energy transfer, rope/spring/water-wave observations, wave features, speed, transverse and longitudinal models, reflection, refraction and ripple-tank diffraction. Extended compares wavelength effects at gaps and edges, including gap size. Written work is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Explain refraction and normal incidence.
- Use v = fλ and consistent front spacing.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the intended role of the plate in this experiment?
What you will learn
- Describe a ripple-tank refraction experiment using a change of depth.
- Interpret speed, frequency and wavelength under the stated stationary conditions.
Use a raised region to change water depth
A teacher-supervised ripple tank can contain a suitable transparent plate that makes water shallower over part of the tank. Use a straight vibrating bar to send fronts toward the depth boundary, with suitable source amplitude, illumination and viewing screen. Under the selected wave conditions, the shallower region has lower propagation speed. Observe spacing on both sides and direction for an oblique boundary.
Keep the source frequency steady and the boundary stationary. Fronts closer together over the plate show shorter wavelength; for unchanged frequency, v = fλ gives lower speed. With oblique entry, the direction is closer to the normal in the slower region. For normal entry, spacing can change without a change of propagation direction.
Compare consistent repeated features
Measure adjacent corresponding fronts along their propagation direction using the observation scale, not an arbitrary distance along the boundary. Several complete wavelengths can improve the spacing estimate when a clear pattern permits it. A supplied 4.0 Hz source with 0.15 m and 0.10 m spacings gives 0.60 and 0.40 m/s; these are teaching values, not real tank measurements.
Disturbed flow, tank-edge reflections or an uncontrolled source change can complicate the comparison. State the actual depth/source conditions and observation method. The plate must create a water-depth boundary rather than a dry solid wall blocking the whole path. A description and supplied calculations do not establish apparatus competence or a completed practical assessment.
Pause and explain
At 4.0 Hz, a measured-model spacing changes from 0.15 to 0.10 m. Which speed comparison follows?
Worked example
Supplied fixed-frequency fronts have spacings 0.15 m in the deeper region and 0.10 m over a shallow plate, at 4.0 Hz. Find speeds.
Show the worked solution
- Use v = fλ for each region.
- Deeper-region speed = 4.0 × 0.15 = 0.60 m/s.
- Shallower-region speed = 4.0 × 0.10 = 0.40 m/s.
Answer 0.60 m/s then 0.40 m/s; source frequency remains 4.0 Hz.
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Describe apparatus and observations for refraction over a shallow region in a ripple tank.
Give me a hint
Use transmission through a depth change with a steady source.
Compare my reasoning
- Use a suitable plate below the water to create two depths.
- Send approximately straight waves at a stationary boundary using a steady source.
- Compare front spacing and, for oblique incidence, normal-referenced direction.
A steady-source depth-boundary comparison shows changed spacing and possible oblique bending.
Look for these in your work
- Describe the plate's purpose.
- State the measured pattern features.
For supplied f = 5.0 Hz, deeper spacing 0.060 m and shallower spacing 0.040 m, calculate speeds.
Give me a hint
Apply the same frequency separately to both repeat lengths.
Compare my reasoning
- Deeper speed = 5.0 × 0.060 = 0.30 m/s.
- Shallower speed = 5.0 × 0.040 = 0.20 m/s.
- The smaller spacing accompanies the lower speed.
0.30 m/s and 0.20 m/s.
Look for these in your work
- Use consistent units.
- Retain fixed frequency.
The source rate changes between the two depth observations. Can spacing alone isolate the depth effect on speed?
Give me a hint
Both frequency and wavelength now enter the comparison.
Compare my reasoning
- v = fλ uses each observation's actual frequency.
- The changed source rate affects spacing independently of a depth change.
- Use a matched steady source or record both frequencies before attributing the difference.
No depth-only conclusion follows from unmatched source frequencies and spacing alone.
Look for these in your work
- Identify the changed variable.
- Specify a fairer comparison.
Common mistakes
- The plate changes depth rather than being a full dry barrier.
- Measure spacing along propagation, not along the boundary.
- No bending is required at normal incidence.
What can you explain now?
Do closer transmitted fronts at unchanged frequency imply a higher speed?
Compare with the explanation
No; lower speed.
The smaller wavelength gives smaller fλ when frequency stays fixed.
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Make it stick
Describe a controlled depth-change tank method and use matched frequency to interpret transmitted spacing.
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