In this experiment, you will investigate convection currents in water. You fills a large glass beaker with cold water and allows it to settle. You gently dr...

(a) The potassium permanganate crystal dissolves to produce a purple colour trail in the water. [1]

(b) The colour trail rises vertically upward from the crystal, directly above the point where the beaker is being heated. [1] It then travels across the top of the beaker and descends on the far side, forming a complete circulation loop. [1]

(c) The water directly above the heat source is warmed and expands, so its density decreases. [1] Because this warm water is less dense than the surrounding cooler water, it experiences a net upward (buoyant) force and rises. [1]

Density is mass per unit volume. Heating increases the volume of a fixed mass of water, which reduces its density. The denser cool water pushes the less dense warm water upward.

(d) When the rising warm water reaches the surface, it is pushed sideways by more warm water continuously rising behind it. [1] As it travels across the top, it cools, becomes denser, and sinks on the far side where there is no heater. [1]

(e) Convection. [1]

Convection is the transfer of thermal energy by the bulk movement of a fluid (liquid or gas). It requires density differences caused by uneven heating.

(f) Measure the vertical distance from the base to the top of the beaker outline in Fig. 36.1 using a ruler. The height is approximately 3.8 cm on the printed diagram (accept any reasonable measurement with a unit). [1]

(g) Place the crystal gently into the water using tweezers, without stirring or disturbing the water. [1] Any disturbance would create artificial currents that interfere with the observation of the true convection pattern.

(h) If the heater were placed directly below the centre, the coloured water would rise straight up in the middle and then spread outward symmetrically in both directions at the surface, sinking down on both sides to form two mirror-image convection loops. [1]