Watching one ripple crossing another

Demonstration

A close look at interference between two, random wave pulses in a ripple tank.

Apparatus and Materials

For the class

• Ripple tank and accessories

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. Make one ripple (pulse} with a finger, and start another ripple from another place some distance away. Watch the two ripples carefully as they pass through each other.
2. What happens when one ripple crosses another? Do they upset each other? Are they changed by the encounter?

Teaching Notes

• The fact that two waves continue on their way when they have passed through each other as if there had never been an encounter will come as no surprise to students who have:
• Closely observed raindrops falling in a puddle, or
• Thought about the fact that signal-carrying microwaves and radio waves pass through each other constantly, particularly in cities dense with communications.
• Still it is remarkable.
• Of course, this only happens for linear systems which obey Hooke’s Law. In non-linear systems, where energy from the passing disturbance is partially absorbed by the medium, waves will permanently affect each other when they pass.

This experiment was safety-tested in February 2006