Compare wavelength effects at a diffraction edge
Explain stronger bending into a geometric shadow for longer wavelengths under matched edge conditions.
Extended only (Supplement); Physics 0625, 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
Before you begin
- Describe a single-edge ripple-tank method.
- Distinguish wavelength from amplitude and source frequency.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which comparison isolates a wavelength effect at one edge?
What you will learn
- Describe how wavelength affects diffraction at an edge.
- Separate qualitative shadow penetration from an exact intensity or angle prediction.
Longer wavelengths bend more around the same edge
At the same edge geometry under otherwise matched conditions, a longer wavelength gives more pronounced diffraction into the geometric shadow. A shorter wavelength gives less pronounced bending. The shadow is defined by a straight-path construction; diffraction is the reason a wave field can extend into it rather than end at an absolute ray-model boundary.
No second barrier end is required for this single-edge comparison. Do not invent a gap width to describe every edge. Wavelength matters relative to the relevant obstacle geometry, while a diagram can illustrate the qualitative trend without supplying an exact boundary between a detectable and undetectable field.
Control geometry and avoid an intensity shortcut
A described tank comparison can retain the same barrier end, incident direction, suitable depth and viewing arrangement while producing and checking different wavelengths. If the source rate changes, document the actual corresponding wavelengths and propagation conditions. Keep amplitudes and visibility adequate for the comparison so a faint pattern is not simply mistaken for less bending.
For supplied wavelengths 1.0 and 4.0 cm at the same edge, the 4.0 cm case gives more pronounced extension into the geometric shadow. This does not establish four times the shadow energy or a numerical diffraction angle. An obstacle drawing without relevant wave properties cannot determine every shadow intensity, and written interpretation remains separate from supervised practical competence.
Pause and explain
For matched edge conditions, which wavelength bends more into the geometric shadow?
Worked example
At one unchanged barrier end, supplied wavelengths are 1.0 cm and 4.0 cm under matched observation conditions. Compare diffraction.
Show the worked solution
- The edge geometry is held fixed.
- The second wavelength is longer.
- The 4.0 cm case gives more pronounced bending into the geometric shadow.
Answer 4.0 cm gives stronger edge diffraction; no exact shadow intensity follows.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare 1.0 and 4.0 cm wavelengths at the same barrier end.
Give me a hint
Retain the edge geometry before applying the wavelength trend.
Compare my reasoning
- The barrier end and incident geometry are matched.
- 4.0 cm is the longer wavelength.
- It gives more pronounced bending into the geometric shadow.
The 4.0 cm wave has stronger edge diffraction under matched conditions.
Look for these in your work
- Hold the edge fixed.
- Describe shadow extension qualitatively.
Describe controls for a tank wavelength comparison at a single edge.
Give me a hint
Keep geometry, propagation and viewing causes separate.
Compare my reasoning
- Retain the same edge and incident direction.
- Check the actual wavelengths and suitable water/source conditions.
- Keep observation and adequate visibility controlled; separate unrelated returns.
Matched edge/incident geometry, checked wavelengths and controlled propagation/viewing.
Look for these in your work
- Name the changed variable.
- Identify the controls.
A sketch gives longer-wavelength fronts curving into a shadow but no amplitude or calibrated intensity. Can it prove an exact fourfold shadow energy?
Give me a hint
The spread trend is not an intensity equation.
Compare my reasoning
- The drawing gives qualitative front geometry.
- No amplitude, measurement or relevant energy model is supplied.
- The exact energy ratio is not established by wavelength ratio alone.
No; wavelength ratio alone does not determine an exact shadow energy ratio.
Look for these in your work
- Separate spread from intensity.
- Identify missing quantitative evidence.
Common mistakes
- A single edge does not need a two-sided gap.
- Longer wavelength gives more pronounced matched-edge diffraction.
- A qualitative trend does not give a numerical shadow energy ratio.
What can you explain now?
Does quadrupling wavelength prove four times the energy at one shadow point?
Compare with the explanation
No.
The syllabus trend concerns relative spreading; intensity needs additional wave and geometry information.
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Make it stick
Explain the matched-edge wavelength trend and reject unsupported intensity or exact-angle claims.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.