3.1.4 Wave Behaviors: Ripple Tank Phenomena
Comprehensive assessment covering Refraction, Diffraction, and Reflection
1Paper 2: Multiple Choice Questions
5 questions testing core understanding
Water waves move from deep water (where they travel faster) into shallow water. What happens to the speed and wavelength of the waves?
Topic: Refraction - Speed & Wavelength Changes
A ripple tank is used to demonstrate diffraction of water waves passing through a gap. When does maximum (most noticeable) diffraction occur?
Topic: Diffraction - Maximum Condition
In a ripple tank, water waves are reflected from a straight barrier. How does the angle of reflection (r) compare to the angle of incidence (i)?
Topic: Reflection - Law of Reflection
A student observes circular wave patterns spreading out after passing through a narrow gap in a barrier in a ripple tank. Which wave behavior is being demonstrated?
Topic: Visual Identification - Diffraction Pattern
Plane water waves in a ripple tank travel from a deep region into a shallow region at an angle to the boundary. What happens to the direction of the wavefronts?
Topic: Refraction - Wavefront Direction
2Paper 4: Structured Theory Questions
Deep understanding with mark schemes
A student investigates refraction of water waves in a ripple tank using a glass plate to create a shallow region.
(a) Describe what the student would observe about the wavelength of the waves in the shallow region compared to the deep region. [2]
Mark Scheme:
wavelength decreases / waves closer together [1]
in the shallow region [1]
(b) The frequency of the wave generator is 5 Hz. In the deep region, the wavelength is 4.0 cm. Calculate the speed of the waves in the deep region. [3]
Mark Scheme:
v = fλ or correct formula [1]
= 5 × 0.04 or = 5 × 4.0 (if units correct throughout) [1]
= 0.2 m/s or 20 cm/s [1]
(c) In the shallow region, the wavelength decreases to 3.0 cm. Calculate the speed of the waves in the shallow region. [2]
Mark Scheme:
v = 5 × 0.03 or correct substitution [1]
= 0.15 m/s or 15 cm/s [1]
(d) Explain why the frequency remains constant even though the speed and wavelength change. [2]
Mark Scheme:
frequency is determined by the source/generator [1]
the generator continues vibrating at the same rate [1]
A student uses a ripple tank to investigate how gap width affects diffraction of water waves. The wave generator produces waves with wavelength 2.0 cm.
(a) State what is meant by diffraction. [1]
Mark Scheme:
spreading/bending of waves through a gap or around an obstacle [1]
(b) The student tests three different gap widths: 1.0 cm, 2.0 cm, and 4.0 cm. Predict which gap width will produce the most noticeable diffraction. [2]
Mark Scheme:
2.0 cm [1]
because gap width is approximately equal to wavelength [1]
(c) Describe what the student would observe with the 4.0 cm gap compared to the 2.0 cm gap. [2]
Mark Scheme:
less diffraction / less spreading [1]
waves continue more in straight lines [1]
(d) The student wants to increase the amount of diffraction while keeping the same 2.0 cm gap. Suggest one way to achieve this. [2]
Mark Scheme:
increase the wavelength [1]
by decreasing the frequency of the generator [1]
3Paper 6: Alternative to Practical
Measurement, observation, and safety
A student sets up a ripple tank experiment to measure the wavelength of water waves. The diagram shows a view of the wave pattern.
(a) A ruler is placed alongside the wave pattern. Five complete waves occupy a length of 12.0 cm. Calculate the wavelength. [2]
Mark Scheme:
wavelength = 12.0 ÷ 5 or correct method [1]
= 2.4 cm [1]
(b) State one way to improve the accuracy of this wavelength measurement. [1]
Mark Scheme:
measure more waves / over a longer distance [1]
OR: repeat and calculate mean [1]
OR: use a magnifying glass to read positions more precisely [1]
(c) The student counts 15 wavefronts passing a fixed point in 3.0 seconds. Calculate the frequency of the waves. [2]
Mark Scheme:
frequency = number of waves ÷ time or f = 15 ÷ 3.0 [1]
= 5.0 Hz [1]
(d) Suggest one safety precaution the student should take when using the ripple tank. [1]
Mark Scheme:
keep electrical components away from water [1]
OR: wipe up spills immediately / keep floor dry [1]
OR: do not touch the lamp when it is hot [1]
⚠️Examiner's Traps - Common Mistakes
Trap 1: Confusing refraction with reflection. Refraction = bending when entering different medium. Reflection = bouncing back.
Trap 2: Thinking frequency changes during refraction. Frequency ALWAYS stays constant (determined by source).
Trap 3: Measuring angles from the barrier instead of from the normal (perpendicular line).
Trap 4: Forgetting to convert cm to m in calculations. Always use SI units in final answers.
Trap 5: Stating "waves get smaller" instead of "wavelength decreases" - precision matters in mark schemes!
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