Episode 113: Preparation for series and parallel circuits
Here, simple ideas about electricity are applied to circuits that have real applications. We begin
by considering the effective resistance when components are connected in series and in parallel.
The link between voltage and energy transfers leads to ideas about energy and power.
Conservation laws (charge and energy) lead directly to Kirchhoff’s laws and these in turn provide
a method for solving a large range of circuit problems, including potential dividers.
Episode 114: Components in series and parallel
Episode 115: Energy and power
Episode 116: Using energy and power equations
Episode 117: Kirchhoff’s laws
Episode 118: Potential dividers
Advance warning
A joulemeter will be useful when discussing energy and power in electric circuits. It is worth
practising with it before using it in any
demonstration.
Find a selection of ready-made potential dividers
(also known as potentiometers). Look for the three
connections, characteristic of a potential divider.
Take the back off a rotary potentiometer to see the
resistive material, and the wiper.
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Main aims
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Students will:
1. Calculate resistances of series and parallel combinations of resistors.
2. Investigate the power of a filament lamp.
3. Use energy and power equations, including calculations of cost.
4. Test and use Kirchhoff’s laws.
5. Use potential dividers to control potential difference and to build a sensor.
Prior knowledge
By this stage, students should be able to distinguish between charge, current and voltage; they
should understand the definition of resistance, and be competent in handling equations involving
these four quantities. However some pupils will probably still be unwittingly harbouring some
misconceptions, for example in the area of potential differences in parallel circuits, so be
prepared to test, rather than to assume knowledge. These misconceptions may well become
apparent in the Episodes 117 and 118.
This topic also revisits ideas about energy transfers in electric circuits.
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Where this leads
Topics remaining in basic electricity include EMF and internal resistance. Then students will be
equipped to understand many different circuits, alternating current, etc.
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