Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Simple circular pulses in ripple tanks

Demonstration

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

Apparatus and materials

Ripple tank and accessories

Pencil

Water Dropper

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.

 

Procedure


Single ripple in tankStart 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


1 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. 

 
2 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-checked in February 2006


Related guidance


Using ripple tanks