Electronics For Dummies
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The diagram shown depicts a battery-operated circuit that powers a light-emitting diode (LED), much like what you might find in a mini LED flashlight. What you see in the figure is a circuit diagram, or schematic, that shows all the components of the circuit and how they are connected.

Current delivers electrical energy from the battery to the resistor and the LED.
Current delivers electrical energy from the battery to the resistor and the LED.

The battery is supplying 6 volts DC (that is, a steady 6 volts) to the circuit. The plus sign near the battery symbol indicates the positive terminal of the battery, from which current flows (conventional current, of course). The negative sign near the battery symbol indicates the negative terminal of the battery, to which the current flows after it makes its way around the circuit. The arrow in the circuit indicates the reference direction of current flow, and because it's pointing away from the positive terminal of the battery in a DC circuit, you should expect the value of the current to be positive all the time.

The lines in the circuit diagram show how the circuit components are connected, using wire or other connectors. Electronic components are usually made with leads — protruding wires connected to the innards of the component that provide the means to connect the component to other circuit elements.

The zigzag symbol in the circuit diagram represents a resistor. The role of the resistor is to limit the amount of current that flows through the circuit, much like a kink in a garden hose restricts water flow. Resistance is measured in units called ohms (symbolized as Ω) and that the resistor in this circuit is keeping the LED from being destroyed.

The LED is symbolized by a triangle with a line segment on one end and two arrows pointing outward. The triangular part of the symbol represents a diode, and the two arrows facing out represent the fact that this diode emits light (hence, it is a light-emitting diode). Diodes are part of a special class of electronic component known as semiconductors.

By building this circuit and taking some measurements of voltages and current, you can learn a lot about how circuits work. And voltage and current measurements are the key to finding out how the electrical energy generated by the battery is used in the circuit.

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Cathleen Shamieh is an electrical engineer and a writer with extensive engineering and consulting experience in the fields of medical electronics, speech processing, and telecommunications.

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