EMF and internal resistance

The work on EMF and internal resistance draws on ideas about voltage, current and charge that were discussed in previous sections. The idea of EMF (electromotive force) has already been introduced but may well need reinforcement, along with the definition of the volt, and there is a lot to be gained by beginning this work with a general discussion of energy transfers within electric circuits. This should link to real-life examples involving energy transfer from a chemical battery to electrical work.

The work on AC and the oscilloscope may not be required by the specification you are following, but is widely useful and may well be worth teaching as an extension. It is best to introduce the oscilloscope with dc supplies before teaching about ac, when it can be used to illustrate the link between peak and r.m.s values.

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