Electric circuits · revision map · IGCSE 0625, Topic 4.3
TOPIC 4.3 · ELECTRIC CIRCUITS
CAMBRIDGE IGCSE PHYSICS 0625 · ONE-PAGE REVISION MAP
thelucidstem.com
ELECTRIC
CIRCUITS4.3
CIRCUITS4.3
Circuit Symbols & Components
Circuits are drawn with standard symbols.
- An ammeter goes in series; a voltmeter in parallel.
Series Circuits
A series circuit is a single loop with one path.
- The current is the same at every point.
- The supply p.d. is shared between the components.
- Resistances add up.
Parallel Circuits
A parallel circuit has more than one path.
- Current splits at a junction and rejoins: what flows in equals what flows out.
- Each branch gets the full supply p.d.
- The combined resistance is less than the smallest branch resistance.
Combined ResistanceEXTENDED
Components combine differently in series and parallel.
In series resistances add:
R = R1 + R2
In parallel add the reciprocals:
1 / R = 1 / R1 + 1 / R2
- Two equal resistors in parallel give half the resistance.
Sensing ComponentsEXTENDED
Some resistances change with their surroundings.
- An LDR has a high resistance in the dark and a low resistance in bright light.
- A thermistor's resistance falls as it gets hotter.
- These let circuits respond to light and temperature.
Potential DividerEXTENDED
A potential divider uses two resistors to split the supply and give a changing output p.d.
- The larger share of the p.d. is across the larger resistance.
- Replace one resistor with an LDR or thermistor to sense light or heat.
- The output p.d. then drives a switching circuit.