The secret alphabet

The idea

Circuit components are represented by symbols: in the cell symbol the long line is the positive terminal and the short line the negative; in the LED symbol the triangle points the direction of current and two arrows show light emission.

Pictures that mean something

Electricians across the world draw circuits with the same little pictures, called symbols. A cell has one, and so does an LED.

A cell has a long line and a short line in its symbol. Which one do you think is the positive terminal?

• The long line
• The short line
• Both are the same

Read the symbols

First the cell. Then the LED.

Symbols

Circuit components are represented by symbols. In the cell symbol the long line is the positive terminal and the short line the negative. In the LED symbol the triangle points in the direction of current, and two arrows show light emission.

• Component | Symbol | What to notice
• Electric cell | two parallel lines, one long and one short | the long line is positive, the short line is negative
• LED | a triangle with a bar, and two arrows | the triangle points the way current can flow; the two arrows show it emits light

Notes

Cell: the long line is positive (+), the short line is negative (–). LED: the triangle points the way current can flow; two arrows show it emits light.

Check yourself

In the symbol for a cell, the long line stands for the...

In the LED symbol, the triangle points...

What do the two arrows in the LED symbol show?

The cell's metal cap is on the right. In its symbol, which line is on the right?

• positive terminal — correct. Yes! Long line, positive terminal.
• negative terminal. The short line is the negative terminal.
• lamp. The cell symbol has nothing to do with the lamp.
• towards the light. The arrows show light. The triangle shows the current.
• in the direction in which current can flow — correct. Yes! The triangle points the way current can pass.
• towards the cell's negative terminal always. It points the way current can flow, which depends on how the LED is joined.
• That the LED emits light — correct. Yes! The arrows leaving the LED show light being given out.
• That current flows both ways. Current passes through an LED in one direction only.
• That the LED is connected to two cells. The arrows are not about cells.
• The long line, because the cap is positive — correct. Yes! Long line = positive = the cap.
• The short line, because it is on the right. The short line is the negative one, the disc.
• Either; it makes no difference. It matters: the long line marks the positive terminal.