3 Basic Circuit Components

Learn how common circuit components control, supply, store, or convert electrical energy, and how their ratings, connections, and behavior affect a circuit.

Circuit components and schematics

Circuit components control, supply, store, or convert electrical energy. In a schematic, each component is represented by a symbol, and lines represent the wires connecting components. Components are chosen both for their function and for ratings such as maximum voltage, current, and power.

Sources and current paths

A provides electrical energy by maintaining a voltage or supplying a current. A battery is a common direct-current (DC) voltage with fixed positive and negative terminal polarities. An alternating-current (AC) periodically reverses its voltage and current direction.

Circuit diagrams may represent ideal sources that maintain a specified voltage or current. Real sources have limits and may have internal resistance. A alone does not guarantee current flow: there must be a complete conducting path between its terminals, and the connected components determine the current and how electrical energy is used.

Resistors, current, and power

A provides resistance, measured in ohms. It limits current and can create a voltage drop. For an ohmic , is:

V = IR

Here, $V$ is the voltage across the , $I$ is the current through it, and $R$ is its resistance. A commonly converts electrical energy into heat. Its power can be calculated as:

P = VI

For an ohmic , power can also be calculated using:

P = I^2R

Choose a with an appropriate power rating so that it does not overheat. For example, a $1\,\text{k}\Omega$ connected across $5\,\text{V}$ ideally carries:

I = \frac{V}{R} = \frac{5}{1000}\,\text{A} = 0.005\,\text{A} = 5\,\text{mA}

Switches and path control

A changes whether a circuit path is electrically connected. An open breaks the path, so ideally no current flows through that path. A closed completes the path and acts approximately like a wire, although a real has small resistance and its own current and voltage ratings. Switches are used to start, stop, or redirect current.

Lamps and LEDs

A converts electrical energy into light. An incandescent uses current to heat a filament until it glows. The filament behaves roughly like a , although its resistance changes as it heats. A ’s rating indicates the voltage or power for which it is designed; supplying too much voltage can cause excessive current and damage.

A light-emitting () is a -based light . It must be connected with the correct polarity and operated within its current rating. Unlike an incandescent , an commonly needs a series or another current-limiting circuit.

Capacitors and changing voltage

A stores separated electric charge and energy in an electric field. Its capacitance, $C$ , is measured in farads and relates charge, $Q$ , to voltage, $V$ :

Q = CV

In the ideal model, a ’s voltage cannot change instantaneously, so it can oppose rapid voltage changes. In a simple DC circuit, current flows while the is charging or discharging. After it has charged to a steady voltage, an ideal carries no steady DC current. Capacitors are used for energy storage, filtering, and timing. Many are polarized and must be connected with the specified polarity.

Inductors and changing current

An is usually a coil of wire that stores energy in a magnetic field when current flows. Its inductance, $L$ , is measured in henries. An opposes changes in current: a changing current induces a voltage that acts against that change.

In an ideal DC circuit, an behaves like a wire after conditions settle, but its response matters while conditions are changing. Inductors are used in filters, power supplies, and magnetic devices such as transformers.

Diodes and current direction

A is a semiconductor component that conducts readily in one direction and resists current in the opposite direction, within its operating limits. Its terminals are called the and . When forward biased, the is at a higher potential than the and current can flow; when reverse biased, the generally blocks current.

A real is not a perfect one-way . Its forward voltage and maximum current depend on its type and operating conditions. Diodes are used for rectification, polarity protection, and light emission in LEDs.

Choosing an series

A simplified example uses a $9\,\text{V}$ to power an with a forward voltage of about $2\,\text{V}$ . For a desired current of $10\,\text{mA}$ , the approximate series resistance is:

R = \frac{9\,\text{V} - 2\,\text{V}}{0.010\,\text{A}} = 700\,\Omega

A nearby suitable value, such as $680\,\Omega$ , gives about $10\,\text{mA}$ in this simplified example. In practice, check the ’s data and the ’s power rating.

Combining components

A simple circuit can combine a , , , and in one loop. Closing the completes the path; the drives current; and the and determine how voltage and energy are distributed.

Adding a or makes the circuit’s behavior depend on time, while adding a makes its behavior depend on current direction. Correct component orientation, ratings, and connections are essential for predictable and safe operation.