4.3.1Electricity and Magnetism
Circuit Diagrams AND Circuit Components — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 11 parts Lesson 31 of 65 1 quiz
Lesson summary
4.3.1 Circuit Diagrams and Circuit Components — IGCSE PHYSICS notes: Draw and interpret circuit diagrams using standard symbols and state the function of each component.Symbols — circuit diagrams use standard symbols joined by straight lines, with no gaps except in open switches.…
- Complete circuit
- Power supplies and generators
- Fixed resistor
- Variable resistor
- Thermistor
- Light-dependent resistor (LDR)
Part 1 of 9Circuit diagrams
Symbols
- Symbols circuit diagrams use standard symbols joined by straight lines, with no gaps except in open switches.
Complete circuit
- Complete circuit a circuit must be complete for current to flow.
Junctions
- Junctions shown with a dot where wires join, and wires crossing without a dot are not connected.
Part 2 of 9Power supplies and switches
1Cell
- Cell a long thin line (+) and a short thick line (−).
2Battery
- Battery two or more cells in series.
3Power supplies and generators
- Power supplies and generators d.c. or a.c. supplies and generators all supply current to the circuit.
4Switch
- Switch a gap in the line that opens and closes the circuit and decides whether current can flow.
Part 3 of 9Resistors
1Fixed resistor
- Fixed resistor a rectangle, used to control current.
2Variable resistor
- Variable resistor a rectangle with an arrow through it, used to change the current, as in a dimmer or volume control.
3Thermistor
- Thermistor a temperature-dependent resistor whose resistance decreases as temperature increases.
4Light-dependent resistor (LDR)
- Light-dependent resistor (LDR) a sensor whose resistance decreases as light intensity increases.
Part 4 of 9Meters
Ammeter
- Ammeter a circle with A, always connected in series.
Voltmeter
- Voltmeter a circle with V, always connected in parallel.
Part 5 of 9Functional components
Functional components
Lamp
- Lamp a circle with a cross that emits light.
Heater
- Heater a rectangle with divisions that transfers thermal energy.
Motor
- Motor a circle with M that rotates.
Generator
- Generator a circle with G.
Bell and buzzer
- Bell and buzzer emit a sound.
Part 6 of 9Electromagnetic components
Electromagnetic components
Relay
- Relay a coil (electromagnet) that operates a switch in a separate circuit, so a small current controls a much larger current.
Transformer
- Transformer two coils on a core that step the p.d. up or down.
Magnetising coil
- Magnetising coil uses the magnetic effect of a current.
Part 7 of 9Fuses and diodes
Fuse
- Fuse a rectangle with a line through it that protects components from current surges and acts as a safety measure against fire.
Diode (Extended)
- Diode (Extended) a triangle pointing towards a bar that allows current in one direction only, the direction the triangle points.
- Flipped, it prevents current from flowing.
LED
- LED a diode with arrows pointing out that emits light when current flows.
Part 8 of 9Drawing a circuit diagram
1
Start with the power supply and mark the + and − sides.
2
Draw the main loop with straight lines using a ruler.
3
Add the components in series using the correct symbols.
4
Add parallel branches with junction dots.
5
Add the ammeter in series and the voltmeter in parallel where needed.
6
Check there are no gaps except in open switches.
Part 9 of 9More from the specification
More from the specification
Standard schematic symbols
- Standard schematic symbols drawing internationally recognized circuit symbols provides a standardized means to communicate electrical network topologies unambiguously.
Circuit symbols
- Circuit symbols standard diagrams represent cells, lamps, resistors, switches, ammeters and voltmeters so circuits can be drawn clearly.
Potential difference
- Potential difference the energy transferred per unit charge between two points;
- a voltmeter is connected in parallel across a component.
Series and parallel
- Series and parallel in series the source voltage is shared and current is equal;
- in parallel each branch gets the full voltage.
Fuses
- Fuses a thin wire in the live lead that melts if current is too high, protecting the appliance and wiring.
Earth and insulation
- Earth and insulation the earth wire carries fault current away from a metal case, and double insulation prevents contact with live parts.
Circuit symbols
- Circuit symbols standard diagrams represent cells, lamps, resistors, switches, ammeters and voltmeters so circuits can be drawn clearly.
Potential difference
- Potential difference the energy transferred per unit charge between two points;
- a voltmeter is connected in parallel across a component.
Series and parallel
- Series and parallel in series the source voltage is shared and current is equal;
- in parallel each branch gets the full voltage.
Fuses
- Fuses a thin wire in the live lead that melts if current is too high, protecting the appliance and wiring.
Earth and insulation
- Earth and insulation the earth wire carries fault current away from a metal case, and double insulation prevents contact with live parts.
Potential difference
- Work done by a unit charge passing through a component.
Combined resistance
- Single resistance that could replace several resistors.
Potential divider
- Series resistors that share the supply p.d.
Mains supply
- Domestic a.c. supply, rated 230 V rms at 50 Hz in the UK.
Source
- Reservoir at TH providing heat QH
Insulation
- Material that reduces thermal energy transfer.
Key terms
| Term | Meaning |
|---|---|
| Circuit symbol | Standard drawing that represents a component. |
| Thermistor | Resistor whose resistance falls as temperature rises. |
| LDR | Resistor whose resistance falls as light intensity rises. |
| Relay | Switch operated by an electromagnet. |
| Diode | Component that allows current in one direction only. |
| Fuse | Safety component that melts when the current is too large. |
Avoid these mistakes
1
Drawing a voltmeter in series — it must be in parallel across the component.
2
Leaving gaps in the circuit diagram — a gap stops the current.
3
Confusing the symbol for a fuse with that of a resistor — the fuse has a wire running through it.
4
Putting the diode the wrong way round — current flows only in the direction the triangle points.
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