Cambridge International AS & A Level · 8 · structured
Plan and explain a ripple-tank diffraction comparison
Plan and explain a ripple-tank diffraction comparison · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 10
- Topics
- 2
- Answer
- Complete
A ripple tank produces plane waves of wavelength20 mm. Adjustable barriers make gaps100 mm and20 mm wide. You may use a dipper, low-voltage vibrator, illumination, a projection screen and rulers.
- (a)
Define diffraction and predict the relative spreading through the two gaps. State what happens to frequency and wavelength after a gap when water depth and driving frequency remain unchanged.
3 marks - (b)
Describe how to make and record a fair comparison, including apparatus arrangement, observations/sketches, controls, wavelength measurement, uncertainty and safety.
7 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Define diffraction and predict the relative spreading through the two gaps. State what happens to frequency and wavelength after a gap when water depth and driving frequency remain unchanged.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
State spreading rather than reflection or a change in speed.
- 2
Compare gap width withλ.
- 3
Frequency stays set by source and wavelength stays fixed when speed is unchanged.
(b)
Describe how to make and record a fair comparison, including apparatus arrangement, observations/sketches, controls, wavelength measurement, uncertainty and safety.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Arrange straight dipper, plane incident fronts and two barriers.
- 2
Set gaps to 100 mm then20 mm, measuring actual opening.
- 3
Keep water depth, drive frequency/amplitude and source position fixed.
- 4
Trace/project transmitted fronts and compare spreading, reducing edge reflections with absorbers.
- 5
Measure multiple crest spacings to establishλ=20 mm; divide total span by interval count.
- 6
Repeat and state ruler/projection-scale or wavefront-position uncertainty.
- 7
Keep power connections dry and use safe low-voltage supply.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) State spreading rather than reflection or a change in speed.
- (a) Compare gap width withλ.
- (a) Frequency stays set by source and wavelength stays fixed when speed is unchanged.
- (b) Arrange straight dipper, plane incident fronts and two barriers.
- (b) Set gaps to 100 mm then20 mm, measuring actual opening.
- (b) Keep water depth, drive frequency/amplitude and source position fixed.
- (b) Trace/project transmitted fronts and compare spreading, reducing edge reflections with absorbers.
- (b) Measure multiple crest spacings to establishλ=20 mm; divide total span by interval count.
- (b) Repeat and state ruler/projection-scale or wavefront-position uncertainty.
- (b) Keep power connections dry and use safe low-voltage supply.
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