50 A transistor, for example, only measures some millimetres. This figure is read ten squared . COLOUR CODING IN ELECTRONIC COMPONENTS Why is colour coding necessary? The electronic components colour code is used for resistors, capacitors, and inductors to indicate the value of their resistance, capacitance, and inductance respectively. These electronic components are very small and it is very difficult to print values on them in the form of numbers. Moreover, the surface of electronic components can often be dirty and worn-out, and this would make it difficult to read numbers. For this reason, manufacturing companies have established an international code which employs colours to indicate the values of electronic components, as coloured bands are much easier to see, print, and recognise than numbers. First digit Second digit Multiplier Tolerance Black Brown Red Orange Yellow Green Blue digit: cifra pattern: modello value: valore worn-out: consumato Colour coding in resistors Most commonly, resistors have four coloured bands; three are grouped together and one is separated from the others. This makes it possible to understand the order in which the bands should be read correctly, i.e. from the most external band of the group three. The first two bands represent the digits that correspond to the value of resistance (for example, in the transistor shown in the picture, the value is 56). The third band represents the multiplier: in the picture, it is 100 (102) . The last band represents the value of tolerance, which in the resistor shown is ±5%. So, as resistance is measured in ohms ( ), the resistor shown performs a resistance of 5,600 ohms with a tolerance of ±5%. 118 ELEcTRONIcS AND ELEcTROTEcHNOLOGY Violet Grey White Gold Silver Colour coding in capacitors and inductors The unit for measuring capacitance is the farad; for a capacitor, however, it is expressed in picofarads (pF). The colour code is the same as that for resistors, but capacitors may have an extra band which indicates voltage. Capacitors bands are drawn vertically and are read from top to bottom. Inductors follow the resistors pattern in colour band printing and the same colour code. The bands show the measurement of inductance, whose measuring unit is the henry, expressed in microhenries (µH). Some inductors have only three bands: in this case, tolerance is considered to be ±20%.