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6.2 Refining the specification

The ideas for the boiler cut-out switch can now be based on some real knowledge about temperature effects. You are now ready to tackle the next exercise.

Exercise 7

List four temperature-dependent changes in material properties t
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6.1 Review

Let's see if we have made any progress in studying thermal effects. The following SAQ is based on Exercise 3, although this time I have a higher expectation of how much you should be able to do.

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5.1 Sudden changes

The third category of thermal effects identified in Section 2 are those associated with sudden changes. Here are some technically important examples where things change suddenly at a particular temperature:

  • Pure water boils at 100 °C (at atmospheric pressure).<
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4.3.3 Getting at the activation energy

The final trick I want to show you with Arrhenius's law is how to extract the constants r0 and Ea from experimental data. If the Arrhenius equation (Section 4.3.1) is ‘turned inside out’ by taking natural logarithms of both sides it becomes:


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4.2.3 The significance of the distribution of energies

Near room temperature (300 K), the average bundle of thermal energy associated with a particle is 0.026 eV (look back at Box 2 Temperature and energy). This is not going to do much damage to something stuck together with bonds that have an energy of a few eV – just as the average wage earne
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4.2 Energy distribution

Atoms without much thermal energy will not be doing very much. Consider fifty million million million (50 × 1018) silicon atoms, bonded into a single massive network; I've chosen silicon, but any elemental solid would do. It will be a speck just large enough to be seen without a microscope. You know that if it is heated it will expand, at some stage it will melt and then eventually it will vaporise – that is because thermal energy effectively ‘rattles it to bits’. Having the
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4.1 Characteristics of processes activated by thermal energy

This is a long section and needs to be studied carefully. Keep your eye on the overall goal of seeking useful thermal effects on which to base devices.

This section continues the discussion of heat at an atomic level. You will need this background to appreciate the characteristics of processes activated by thermal energy – for example, the softening of glass in a gas flame, the diffusion of atoms through solids, the electrical conductivity of ceramics, and many chemical reactions. Suc
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3.4 Summary of Section 3