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

Convection currents in a beaker of liquid

Class practical

Observing convection currents in a beaker of water.

Apparatus and materials

For each group of students

Bunsen burner


Glass tube, approximately 150 mm long x 3 mm internal diameter

Pyrex beaker, 600 ml

Potassium manganate VII crystals

Health & Safety and Technical notes

You need to get the potassium manganate VII crystals into the beaker of water without colouring it unduly. Put a glass tube into the beaker so that it rests on the base of the beaker. Then drop the crystal through the tube.



Apparatus set-up

a Fill the beaker with water. Put individual crystals of potassium manganate VII on the bottom of the beaker.
b Heat the water gently over the Bunsen burner and observe the motion of the dye. For a clear effect, use a small flame and no gauze between Bunsen and beaker (Pyrex beakers do stand this).
c Note the path that the coloured water takes from the heater to the top of the water and back down again.
When repeating the experiment you should always start with a new batch of cold water. 


Teaching notes

This experiment was safety-checked in August 2007


User suggestion

Paula Phillips : 24 April 2006
Try an ice cube with food colouring in (green is best) and the convection current is reversed. It's a great reversal of thought. Students have to understand the process.


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