In electronics, you work with things you can measure. For instance, you need to say how many volts are at a certain point in a circuit, how much current flows through a wire, or how much power an amplifier provides. In this part, we’ll learn about the units and symbols used for different electrical things. We use metric prefixes along with engineering notation as a kind of “shortcut” for certain powers of ten that are commonly used.
In electronics, letters are used to show both quantities and their units. One letter represents what we are measuring, and another letter represents the unit of measurement. For example, the italic letter P stands for power, and the nonitalic (Roman) letter W stands for watt, which is the unit of power. Usually, italic letters mean quantities, and nonitalic letters mean units. Also, notice that energy is written with an italic W, which stands for work. Both energy and work share the same unit, the joule.
Symbols in Electronics
Here are some examples of electrical quantities and their symbols:
- Capacitance (C) – measured in farads (F)
- Charge (Q) – measured in coulombs (C)
- Conductance (G) – measured in siemens (S)
- Current (I) – measured in amperes (A)
- Energy or Work (W) – measured in joules (J)
- Frequency (f) – measured in hertz (Hz)
- Impedance (Z) – measured in ohms (Ω)
- Inductance (L) – measured in henrys (H)
- Power (P) – measured in watts (W)
- Reactance (X) – measured in ohms (Ω)
- Resistance (R) – measured in ohms (Ω)
- Voltage (V) – measured in volts (V)
Apart from these, the SI system has many more units based on fundamental units like meter, kilogram, second, ampere, kelvin, and candela. In 1954, these units became the basic SI units, forming the mks units (meter-kilogram-second). These are commonly used in scientific and engineering work. Another older system, the cgs system, used centimeter, gram, and second as fundamental units. Some units still in use, like the Gauss, are based on the CGS system. In this text, we use mks units unless stated otherwise.