Once we have understood the notion of heat and temperature, and how we can measure the latter, we could ask ourselves how bodies are heated.  Is the increase in temperature proportional to the energy which we supply in the form of heat?

In the following visual we deal with these questions.  We have a substance which is heated by a heater the power of which, in W, we can select with the appropriate control; we can also select the mass of the substance we are heating, as well as its initial temperature.

Using a thermometer we can follow the increase in the temperature of the substance, and the time taken, in the graph on the right temperature is plotted against time (the heating curve).  In this visual we have chosen water as the substance to be worked with as it is easy to understand.