Circuit diagrams
Drawing a circuit with agreed symbols.
A map of a circuit
An electrician draws the plan of a circuit for a classroom. Instead of drawing the real bulbs and cells, the plan uses small standard marks.
Why does a circuit diagram use symbols for the components?
What this lesson covers
The idea
A circuit is drawn as a schematic diagram in which components such as cells, batteries, keys, wire joints, bulbs, resistors, rheostats, ammeters and voltmeters are represented by conventional symbols.
A map of a circuit
An electrician draws the plan of a circuit for a classroom. Instead of drawing the real bulbs and cells, the plan uses small standard marks.
Why does a circuit diagram use symbols for the components?
- It is a convenient way to show a circuit with a simple drawing
- Real components cannot be drawn on paper
- Each symbol shows the exact size of the real component
Meet the symbols
Open every tab. Each symbol has a name under it.
A shorthand
A circuit diagram is a schematic drawing. Everyone uses the same conventional symbols, so anyone can read the circuit without needing the real parts.
A circuit is drawn as a schematic diagram in which components such as cells, batteries, keys, wire joints, bulbs, resistors, rheostats, ammeters and voltmeters are represented by conventional symbols.
Notes
A circuit is drawn as a schematic diagram using conventional symbols for cells, batteries, keys, joints, bulbs, resistors, rheostats and meters.
Check yourself
In a circuit diagram, a battery is the symbol for what?
Which letter is written inside the symbol of an ammeter?
In the pictures, wires cross with no dot at the crossing. What does it show?
Why is a circuit drawn as a schematic diagram?
- A single cell only. A single cell has its own symbol. A battery symbol is for a combination of cells.
- A combination of cells — correct. Yes!
- A bulb. A bulb has a separate symbol of its own.
- V. The letter V is inside the symbol of a voltmeter.
- R. The letter R is used for the resistance of a resistor, not inside a meter symbol.
- A — correct. Yes!
- The wires cross without joining — correct. Yes!
- The wires are joined at that point. A wire joint is shown with a dot. Without the dot the wires only cross.
- The wires are broken at that point. A break would be shown as a gap, for example in an open key. Crossing wires are not broken.
- Because real components cannot be joined by wires. Real components are joined by wires. A schematic diagram only makes the drawing convenient.
- Conventional symbols make it convenient to draw — correct. Yes!
- Because the symbols show the true colour of each part. Symbols are simple marks. They do not show colour or size.