## Amps

Amps (Amperes) measure the flow of current that a potential difference forces through a circuit. The symbol is always A. The name derives from the French physicist André-Marie Ampère (1775-1836). As with Volts, current can be unidirectional – Direct Current (DC) – or alternating in direction (AC), and the values used can be peak or…

## Volts

Volts (symbol V – not v) measure the electrical pressure, or potential difference available to force current through a circuit. The name derives from the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery. Voltages can have a fixed polarity (Direct Current volts), or can change more or less cyclically…

## Watts

Watts are a measure of power. The symbol is W (never w). Electrically Watts = Amps x Volts. The name derives from Scottish engineer and inventor James Watt (1736 – 1819) in honour of his work that transformed the primitive steam engine into a practical power unit. Watts are obviously useful for indicating the power…

## Ohms

Ohms are a measure of the resistance to a flow of current. The name derives from the German physicist Georg Simon Ohm (1759-1854). The symbol for the ohm is the Greek capital letter omega. If the Greek letter cannot be used, the word ohm is used instead. In a simple circuit the relationship between the…

## Balanced line

Balanced lines are typically – and quite incorrectly – explained as follows. A signal is split into two equal but antiphase parts in a balanced line driver. These signals are connected to each leg of a pair cable and eventually arrive at a balanced receiver. This device inverts one leg of the signal. In doing…

## Impedance

Electrical impedance is effectively resistance in an AC circuit (see Ohms). Impedances are significantly more complicated than simple resistance because they are frequency conscious and because they can apply to the behaviour of an entire circuit rather than a single element. There are load impedances, having the effect of a virtual resistor across the input…