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Investigating Wave Experiments


To investigate constructive and destructive interference of pulses in a ripple tank.


    Time Allocation: 45 Min

    Waves come in many forms. There are mechanical waves, such as water waves, sound waves and earthquake waves. There are also electromagnetic waves, such as radio, television, microwaves, visible light, and X-rays. All waves have properties in common. This experiment enables students to discover what the wave properties of water are and to learn to visualize them.

    Reflection involves a change in direction of waves when they bounce off a barrier. Regardless of the angle at which the wave fronts approach the barrier, one general law of reflection holds true: the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier, this is known as the law of reflection. Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves

    Refraction of waves involves a change in the direction of waves as they pass from one medium to another; and diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. Water waves have the ability to travel around corners, around obstacles and through openings. This ability is most obvious for water waves with longer wavelengths. Diffraction can be demonstrated by placing small barriers and obstacles in a ripple tank and observing the path of the water waves as they encounter the obstacles. The waves are seen to pass around the barrier into the regions behind it; subsequently the water behind the barrier is disturbed. The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the waves is smaller than the obstacle, no noticeable diffraction occurs.

    When the vibrator is set to produce single pulses and the power supply is switched on, a single set of transverse pulses  move through the water medium. When the pulses meet each other and constructive and destructive interference take place. Where two crests or two troughs meet, constructive interference takes place. Where a trough and a crest meet destructive interference takes place.



    • Ripple tank with vibrator
    • Water
    • Power supply
    • Light source
    • White paper – size A3


      PART 1: Assembling the Ripple Tank
      1. Take a look at the complete image above before assembling the ripple tank, familiarize the numbers and components before you start putting the pieces together.
      2. Collect the seven rods and identify the four legs 2 (thicker at one end) and the three support rods 3 and 4.
      3. Push the four legs into the corners of the underside of the ripple tank 1.
      4. Turn the ripple tank upright and then push the support rods 3 and 4 into place.
      5. Attach the boss head 17 to the lamp support 3, the middle rod.
      6. Connect the lamp holder and lamp 13 to the other side of the boss head, ensure that the lamp’s flex drops away from the ripple tank.
      7. Attach the motor hanging clips 18 to the motor supports 4.
      8. Connect the springs 15 to the motor hanging clips.
      9. Attach the ripple bar with motor 16 to the other end of the springs.
      10. Adjust the height of the ripple bar with motor 16 by moving the motor hanging clips 18 up or down as necessary.
      11. The ripple bar floats should be about 0.5cm above the surface of the ripple tank 1.
      12. Connect the motor wires to the ripple tank supply unit 12.
      13. Connect the lamp up to a suitable 6v power supply and turn it on.
      14. Fill the ripple tank with water to a depth of approximately 1 cm.
      15. Place a white piece of A4 paper under the ripple tank between the 4 legs of the base.
      16. The ripple tank is now ready to use.
      PART 2: Inducing waves
      1. It is possible to demonstrate reflection of waves off both plain and curved surfaces using the ripple tank.
      2. Move the ripple float bar so that it will produce a straight wave (see operating instructions).
      3. Adjust the ripple tank supply unit to get a wave with a wavelength of approximately 1 cm.
      4. Place one of the straight metal reflectors at an angle of 45 ° and it should be possible to see the wave fronts reflecting.
      5. If necessary adjust the motor speed to gain the clearest wave image under the ripple tank.
      6. The angle reflection can be altered by moving the reflector.
      7. Use the curved metal strip to demonstrate reflection at concave and convex surfaces.
      8. Draw your observations.
      9. Locate the clear plastic shapes they will be needed to demonstrate
      10. The ripple float bar should be adjusted so that it gives a straight wave (see operating instructions).
      11. Place the rectangular shape so it is submerged length wise away from the ripple float bar.
      12. The waves should pass over it but the water above it is much shallower than the rest of the ripple tank. It might be necessary to adjust the volume of water a little.
      13. It should be possible to see that the wave fronts passing over the rectangular shape are becoming refracted and getting closer together when compared to the rest of the ripple tank.
      14. The rectangular shapes position can be altered and the other shapes can also be used to demonstrate refraction further.
      15. Draw your observations.
      16. The L shaped metal gates will be needed to demonstrate refraction.
      17. Set the ripple float bar so that a straight wave is produced (see operating instructions). Adjust the motor speed to get waves with a wave length of approximately 2 cm. Place two of the L shaped metal gates so that there is only about a 1 cm gap between them . A diffraction pattern similar to a single float pattern should be seen passing through the gate.
      18. By adjusting the speed of the motor the amount of diffraction can be changed. Opening up the gate will reduce the amount of diffraction.
      19. To show diffraction of a wave equivalent to a sound wave passing over a wall, use just one L shaped metal gate. The wave behind the gate will slowly spread out again after it has passed by. Waves with longer wavelengths will be diffracted more that those with shorter wavelengths.
      20. Draw your observations.
      21. To demonstrate interference the ripple float bar will need to be fitted with two ball floats which should be separated by about 10 cm in distance.
      22. The motor speed can then be adjusted to get the best interference pattern. It should be possible to see regions of constructive and destructive interference.
      23. Adjusting the distance between the ball floats by decreasing the space between them will alter the shape of the interference pattern.
      24. Observe the waves as you bring the ball floats closer and closer to each other.
      25. Adjusting the speed of the motor will also alter interference patterns.


      Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Refraction is the change in direction of waves that occurs when waves travel from one medium to another. Refraction is always accompanied by a wavelength and speed change. Diffraction is the bending of waves around obstacles and openings. When two pulses meet each other on the same side of the rest position (two crests or two troughs) the resulting amplitude is bigger and constructive interference occurs. When two pulses meet each other on opposite sides of the rest position, (a trough and a crest) the resulting amplitude is smaller and destructive interference occurs.


      • Electric wires must be insulated properly.
      • Do not allow conducting wires to touch water.
      • Keep hands away from vibrator beads when the vibrator is switched on.
      • Beware of water on the laboratory floor, make sure you clean any spills before students slip or fall.
      • Place the power supply for the lamp on a bench, not on the floor by the tank