Thermal convection currents in water can be imaged by using a beaker as a lens!
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Theory
Convection currents can be created by vertical thermal gradients. In a column of fluid, warmer liquid will always want to be high in the column than cooler liquid (and vice-versa). The changes in density across the gradient serves two purposes in this demonstration. It leads to the convection "blooms" but also causes optical changes that allow us, with proper lensing, to see the currents.
Apparatus
- pyrex glass beaker
- warm water, ice
- hot plate
- streaming video camera if you plan on showing it to a large class.
Procedure
- Fill the beaker with lukewarm tap water
- Place an ice cube on the surface of the water as gently as possible. You don't want to disturb the warm water any more than is necessary.
- Using the beaker glass as a lens, you should soon be able to see the cold water melting off the cube.
- For the heating, place the beaker on the hot plate and turn it on.
- Carefully watch for the warm water ripples to start rising in the column. Be sure the hot plate is not set so high as to cause any boiling.
