Topic H: Electrical circuits

Electrical circuit symbols

Electrical circuit symbols

Electrical circuit symbols

Series and parallel Each of the circuit symbols represents a component which can be put in a circuit. A circuit must be complete for a current to flow. Components can either be used in series or in parallel.   Series components are placed one after the other in the same loop of the circuit and the current which passes through each component is the same. Two lamps in series in a circuit:

Series and parallel Parallel components are connected between the same two points in a circuit and the voltage drop across each component is the same. Two lamps in parallel

Measuring instruments A voltmeter is used to measure voltage drop (in volts, V) across a component in a circuit or the potential of the source of electrical energy in a circuit. The source of electrical energy is a cell or battery. To measure the voltage drop, the circuit must be complete. As a cell or battery generates a voltage, the voltage drop across a cell or battery can be measured without it making up part of a circuit. A voltmeter has a high resistance and is always placed in parallel with the component in a circuit. A volt is a Joule per Coulomb: V = E/Q  A voltage drop across a component in a circuit is a measure of the energy needed to move a unit of charge through the component.

Measuring instruments An ammeter is used to measure the current passing through a component in a circuit. An ammeter has a low resistance and is always placed in series with a component in a circuit. All measurements are made in amperes (amps, A). A current has the symbol I and is the flow of charge around a circuit. An amp is a flow of charge of one Coulomb each second: I = Q/t.