Why does water get hot in a kettle

Putting water into an electric kettle does not cause the water to get hot. The water stays cold until we turn on the power to the kettle element, which converts electrical energy from the mains into heat energy. The heat energy from the kettle element is then absorbed by the water, which gets hot as a direct consequence. 

The temperature of the water does not increase much if a small amount of electrical energy is consumed conversely, the water gets hotter if a greater amount of energy is consumed and thereafter passed to the water. A physical chemist says a relationship exists (in this case) between heat input and temperature, i.e. the temperature of the water depends on the amount of energy consumed. 

Mathematically, we demonstrate the existence of a relationship by writing T = /(energy), where T is temperature and the small / means is a function of . 

So the concept of variables is more powerful than just changing parameters nor do physical chemists merely vary one parameter and see what happens to others. They search for physicochemical relationships between the variables. 

In words, the symbols T = f(energy) means T is a function of energy. Note how variables are usually printed in italic type. 

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