Temperature and heat

"Turn up the heat!"

"Raise the temperature!"

"Cool down!"

The words temperature and heat tend to be used interchangeably in day-to-day language. However, they are not synonymous. It is important that physicists distinguish between these key words. 


Key Concepts

What is temperature?

Temperature is defined according to the zeroth (yes, really!) law of thermodynamics:

If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

 In practical terms, temperature is the concentration of heat energy in a body. It dictates the overall direction in which heat energy will transfer (from hot to cold).

 To measure temperature we need a thermometer. To calibrate a thermometer, two fixed points and a measurable physical property such as the length of a column of mercury are needed.

 Which two fixed points do you think would be most convenient?

 Note that many students assume that this experiment should be carried out over a large temperature range. This can be beneficial for increasing the range of validity, but specific heat capacity actually varies slightly with temperature.

Method of mixtures

An alternative way of measuring specific heat capacity is by mixing a hot amount of matter of unknown c with a cold amount with known c.

heat from the hot body = heat to the cold

\((mcΔθ)_{\text{hot}} = (mcΔθ)_{\text {cold} }\)

 Exam questions can sometimes make this trickier by including the concept of flowrate. In this case, you will use the mass of liquid passing a contact surface per second, \(\Delta m\over \Delta t\). You could even be given volumetric flow rate and density (in which case \({\Delta m\over \Delta t}=\rho {\Delta V\over \Delta t}\)).  By considering what happens in a unit time and multiplying everything by 1, the equations simplify to that above. This is a similar approach to that used in Newton's second law for fluids.

Summary

 If different materials are heated at the same rate, the one with the lowest c will have the larger rise in temperature for the same period of time.

Test Yourself

Use quizzes to practise application of theory. 


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Exam-style Questions

Online tutorials to help you solve original problems

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