Progressive Wave
Light, Sound and Waves

Simple circular pulses in ripple tanks

Practical Activity for 14-16 PRACTICAL PHYISCS

Demonstration

Good questions will encourage close observations of circular pulses in a ripple tank.

Apparatus and Materials

Health & Safety and Technical Notes

Beware of water on the laboratory floor. Make sure you have a sponge and bucket handy to mop up spills immediately.

Place the power supply for the lamp on a bench, not on the floor by the tank.

Read our standard health & safety guidance

Procedure

  1. Start a single ripple somewhere in the middle of the tank and then making several such ripples one after the other. Show this can be done using:
  • Finger
  • Pencil to touch the water
  • Drop of water from an eye dropper
  • Ask:
    • What is the shape of the pulse as it travels out?
    • Is the speed of travel the same in all directions? How can you tell?
    • Is the speed the same near to the centre of the tank and at the edges?
    • Is the water moving along with the wave pattern? Drop a scrap of paper onto the water to see if it travels.
  • Let students suggest their own tests. Any materials that students suggest for a test can be fetched quickly; and if they suggest none, the problem had best be left unsettled.
  • Teaching Notes

    • Possible learning outcomes from this experiment:
      • Students become more familiar with the ripple tank.
      • They find that the water does not move out with the ripple.
      • They learn what is meant by a circular ripple.
      • They deduce that it is circular because – if the water is of constant depth – the disturbance travels with the same speed in all directions.
      • They might deduce what happens to the ripple speed if the water depth increases.
    • Pulses will be circular if the tank is level. A circular wave train demonstrates that waves travel the same distance in the same time.

    This experiment was safety-tested in February 2006

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