# Current and EMF

Students will have met basic electrical ideas at GCSE, particularly current, potential difference and energy. However it is useful to revisit all the basics again at A level as students often have developed misunderstandings, for example, in how current flows round a circuit and what affects it.

• electric current as rate of flow of charge, I = Δq/Δt
• It is useful to discuss and think about electron flow vs convential current here. Calculation of drift velocity is a useful challenging introduction to electricity. Also get students to work out number of charge carriers that are required for one coulomb of charge.
• EMF and potential difference
• potential difference in terms of energy transfer
• The definitions are important and this is a difficult part of the topic to get right. Emphasis should be made on the energy transferred or work done by the power supply or battery and the components in the circuit.
• definition of EMF and concept of internal resistance
• The trickiest part of the electricity topic. It sometimes benefits students to leave this until they have a strong understanding of the potential divider, as this essentially is the same mathematical problem. Emphasis on the different forms of the formula and relating it back to V = I R is important. Students find this topic very challenging. It's worth breaking up the topic to revisit the ideas as students gain confidence with circuit calculations.

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