3.1.5Waves
Ripple Tank — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 7 of 35 1 quiz
Lesson summary
3.1.5 Ripple Tank — IGCSE PHYSICS notes: Describe how a ripple tank shows reflection, refraction and diffraction of water waves and how to measure wave speed.Ripple tank — a shallow transparent tray of water that makes water waves visibleLamp and screen — a lamp above the tank pr…
- Wave source
- Level tank
- Curved barrier
- Gap about one wavelength
- Wavelength effect
- Blurred image
Part 1 of 6Apparatus
Ripple tank
- Ripple tank a shallow transparent tray of water that makes water waves visible
Lamp and screen
- Lamp and screen a lamp above the tank projects the wavefronts onto a screen below, where crests and troughs show as bright and dark stripes
Wave source
- Wave source a motor-driven vibrating bar gives plane waves and a dipper gives circular waves
Frequency
- Frequency set by the motor speed, and a higher motor frequency gives a shorter wavelength
Level tank
- Level tank the tank must be level so the depth is the same everywhere
Edges
- Edges sloping sponge or foam absorbs waves and prevents unwanted reflection
Part 2 of 6Demonstrating reflection
Set-up
- Set-up place a metal bar as a plane barrier in the path of the waves
Result
- Result wavefronts reflect so that angle of incidence equals angle of reflection
At 45°
- At 45° the incident and reflected wavefronts meet at right angles
Curved barrier
- Curved barrier reflected waves converge to a focus
Part 3 of 6Demonstrating refraction
Set-up
- Set-up a glass block sits below the water surface and covers part of the tank floor
Depth
- Depth the water is shallower over the block, and speed depends on depth
Result
- Result waves slow down over the block and the wavelength becomes shorter
Frequency
- Frequency stays the same on both sides
Direction
- Direction waves meeting the boundary at an angle bend towards the normal in the shallow region
Part 4 of 6Demonstrating diffraction
Gap
- Gap place barriers to form a gap, and when it is much wider than the wavelength the waves pass almost straight through
Gap about one wavelength
- Gap about one wavelength the waves spread out into almost circular wavefronts
Edge
- Edge waves curve around the edge of a single barrier into the region behind it
Wavelength effect
- Wavelength effect lower motor frequency gives a longer wavelength and more diffraction
Unchanged
- Unchanged wavelength, speed and frequency are not changed by diffraction
Part 5 of 6Measuring wave speed
1
Set up the tank with the lamp above and a screen below.
2
Measure the distance across several wavefronts on the screen and divide by the number of waves to find the wavelength.
3
Allow for magnification of the image by comparing with a ruler placed in the tank.
4
Find the frequency from the motor or by counting waves passing a point in a set time, using a strobe light to freeze the pattern.
5
Calculate v = fλ.
6
Repeat and average.
Part 6 of 6More from the specification
More from the specification
The Fundamental Wave Equation
- The speed v of a progressive wave in a given medium is related to its frequency f and wavelength λ by the wave equation v = f λ.
Transverse Wave Motion
- In transverse waves,
- such as surface water ripples in a ripple tank, the oscillations of medium particles are perpendicular to the direction of energy propagation.
Longitudinal Wave Structure
- In longitudinal waves,
- such as sound waves, particles oscillate parallel to the direction of wave energy transfer, creating alternating compressions and rarefactions.
Wave Amplitude and Undisturbed Rest Position
- Amplitude is defined as the maximum displacement of an oscillating particle from its undisturbed equilibrium position, representing the energy carried by the wave.
The Fundamental Wave Equation
- The speed v of a progressive wave in a given medium is related to its frequency f and wavelength λ by the wave equation v = f λ.
Transverse Wave Motion
- In transverse waves,
- such as surface water ripples in a ripple tank, the oscillations of medium particles are perpendicular to the direction of energy propagation.
Longitudinal Wave Structure
- In longitudinal waves,
- such as sound waves, particles oscillate parallel to the direction of wave energy transfer, creating alternating compressions and rarefactions.
Wave Amplitude and Undisturbed Rest Position
- Amplitude is defined as the maximum displacement of an oscillating particle from its undisturbed equilibrium position, representing the energy carried by the wave.
Amplitude
- Maximum displacement from equilibrium.
Medium
- Material through which light travels.
Position
- Location relative to a reference point.
Period
- Time for one revolution.
Longitudinal wave
- Wave whose vibrations are parallel to the direction of travel
Transverse wave
- Wave whose vibration is at right angles to the direction of propagation
Energy transfer
- Movement of energy from one store to another.
Key terms
| Term | Meaning |
|---|---|
| Ripple tank | Shallow tray of water used to show water waves |
| Plane wave | Wave with straight wavefronts |
| Stroboscope | Flashing light used to freeze the wave pattern |
| Dipper | Source that makes circular waves |
| Refraction | Change of speed of a wave when depth or medium changes |
Avoid these mistakes
1
Saying the frequency changes over the glass block — only speed and wavelength change.
2
Calling the change of direction over a depth change diffraction — it is refraction.
3
Measuring one wavelength only — measure across several wavelengths and divide.
4
Forgetting magnification of the screen image — compare with a ruler in the tank.
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