Learning objectives
Use the standard circuit symbols — cells, resistors, variable resistors, diodes, thermistors, LDRs, ammeters, voltmeters, switches and potentiometers — to draw and read circuit diagrams.
Define e.m.f. (emf) in terms of the energy a source gives each coulomb, contrast it with p.d. (energy converted from electrical form in a component), and use V = E − Ir to explain why terminal p.d. falls as current rises.
State Kirchhoff's first and second laws and link them to conservation of charge and conservation of energy.
Derive the series and parallel resistance rules from Kirchhoff's laws, and set up junction and loop equations to find unknown currents and p.d.s in multi-loop circuits.
Calculate the output of a potential divider, and explain how putting a thermistor or LDR in one arm makes a sensor whose output p.d. changes with temperature or light level.
Explain how a potentiometer wire compares two e.m.f.s or p.d.s by finding balance lengths, and why a galvanometer reading zero at balance makes this a null method.
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