Circuit Diagrams and Circuit ComponentsCambridge IGCSE Physics: Revision notes
Section 1
Drawing and Reading Circuit Diagrams
Electric circuits are represented using standard circuit symbols, so that any circuit can be drawn or interpreted the same way anywhere in the world.
Components you must be able to draw and recognise include: cells, batteries, power supplies, generators, potential dividers, switches, fixed and variable resistors, heaters, thermistors (NTC only), light-dependent resistors (LDRs), lamps, motors, ammeters, voltmeters, magnetising coils, transformers, fuses and relays.
Learn the standard symbol for each component so you can both draw circuits from a description and correctly interpret circuits given in exam questions.
Section 2
Diodes and LEDs in Circuits
Diodes and light-emitting diodes (LEDs) are components that behave differently depending on the direction of current.
- In forward bias, a diode or LED allows current to flow through it with very low resistance.
- In reverse bias, a diode or LED blocks current almost completely, behaving like a very high resistance.
- An LED also emits light when current flows through it in the forward direction.
Don't forget the arrow direction in the diode symbol shows the direction conventional current is allowed to flow (forward bias).
Section 3
Measuring Instruments in a Circuit
Two key measuring components appear in most circuit diagrams:
- The ammeter measures current and is always connected in series with the component being investigated.
- The voltmeter measures potential difference and is always connected in parallel across the component being investigated.
Section 4
Building Series and Parallel Circuits
Components can be connected in a circuit in two basic arrangements.
- In a series circuit, components are connected one after another in a single loop, so the same current flows through each.
- In a parallel circuit, components are connected across separate branches, so current can take more than one path.
Knowing how to construct and use both arrangements is essential for building circuits correctly from a diagram.
Must Know
- Standard symbols are used to draw and interpret circuit diagrams for cells, resistors, thermistors, LDRs, ammeters, voltmeters, transformers, fuses, relays and more.
- Diodes and LEDs conduct in forward bias and block current in reverse bias; LEDs also emit light.
- Ammeters are connected in series; voltmeters are connected in parallel.
- Series circuits form a single loop; parallel circuits provide separate branches for current.
That's the notes covered.
Carry on to the next subtopic.