What to do. Set up the heater and the ice, press Start heating, and read the thermometer at 0 minutes. The stopwatch then stops at every whole minute. Look at the reading window: it shows the thermometer magnified, with a mark for every 1 °C. Find the top of the red line, type the temperature, and press Record. Keep going until the water has been boiling for a few minutes, then press Finish. Your table can be copied into a spreadsheet to draw the graph.

How to read a thermometer. Look straight at the scale (at the level of the top of the liquid). Read the mark that is nearest to the top of the red line. If it is between two marks, estimate. Your reading is accepted if it is within 1 °C of the true value.

What to look for. Watch the table as well as the picture. How does the temperature change when the ice starts to melt? What happens to the temperature while there is still ice in the beaker? What does the water look like as it gets hotter, and what does the temperature do when it boils? The heater supplies energy at a steady rate all the time, so the answers say something about where that energy goes.

The physics behind the model. The heater delivers a fixed power (100, 150 or 220 W reaches the water, in the Gentle, Medium and High settings). The energy goes into (1) warming the ice, with specific heat capacity 2100 J kg⁻¹ K⁻¹, (2) melting it, with latent heat of fusion 334 kJ kg⁻¹, (3) warming the water, 4186 J kg⁻¹ K⁻¹, and (4) boiling it, with latent heat of vaporisation 2260 kJ kg⁻¹. The glass of the beaker also has to be warmed (90 J K⁻¹), and the beaker loses heat to the room (0.5 W for each degree above the room temperature of 22 °C), so the heating slows down as the water gets hot.

Q = mcΔT (warming), Q = mL (melting or boiling)

Simplifications. The water and the ice are stirred, so the thermometer reads the same temperature everywhere. The thermometer reads perfectly, and the water boils at 100 °C. In a real experiment the readings are a little untidy: the temperature does not stay at exactly 0 °C if the water is not stirred, and the boiling point depends on the air pressure and on dissolved substances.

Safety in the real experiment. Wear safety glasses, tie back long hair and keep the bench clear. Use a heat-proof mat, a tripod and gauze, and light the Bunsen burner properly. Do not touch the beaker, the tripod or the thermometer when they are hot. Steam and boiling water cause bad burns: keep your face away from the steam. Never let the thermometer rest on the bottom of the beaker, because the glass is much hotter than the water. Take the heater away before you move the beaker.