Measuring temperature

  Fig. 1-1 Can our finger be a good thermometer?

When you go into a kitchen, what hot and cold objects can you find? A can of coke in the refrigerator is cold, but not as cold as the ice cubes in the freezer. Boiling water inside the kettle is hot, but not as hot as the oil used to prepare French fries.

Everything has a certain degree of hotness or coldness measured by its temperature. The temperature of boiling water is much higher than that of ice cubes because it is much hotter. You can feel cold and hot by placing your hand on an object, but as you will learn in the following activity, temperature measurement based on our senses are subjective and not trustworthy.

Activity: Can our fingers be good thermometers?

  Fig. 1-2 Can we tell the temperature of the oil from the appearance of the French fries?

So how can we measure temperature objectively? We can make use of materials with properties that change with temperature. Have you seen your mother preparing French fries in the kitchen? If the temperature of the oil used is too low the French fries will be raw, but oil at a very high temperature will scorch the fries. The appearance of the fries can therefore serve as a primitive 'thermometer' to indicate the temperature of the oil. See the movie on preparing French fries.

Preparing French fries   Play [Low | High]    Download [Low(623kb) | High(1.07mb)]
Preparing French fries by frying them in oil of different temperatures for 1 minute. Notice the colour and appearance of the French fries change as the oil temperature increases.