Simple straight pulses
Observing what happens when straight wave pulses are produced in a ripple tank.
Apparatus and materials
For each group of students
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.
Lay the rod in the tank and produce a pulse by giving it a tiny but sharp roll forwards and back (see diagram). You may find that it is sufficient just to tap the rod. You can produce continuous waves by repeating this motion periodically.
Ask: Do the ripples change as they move away from the rod? If so, how?
Students should observe that the ripples are rather wide near the rod but become sharper as they move away.
The ripples are sharpest when the filament of the lamp is parallel to them. (This is why special 48 W lamps are required.)
This experiment was safety-checked in February 2006