Circuit Symbols

Thunderstorms with mesmerizing lightning displays reveal the transfer of energy through electric currents. Electric currents used in daily life originate from power stations, which distribute electricity to substations and homes. Electric circuits govern the operation and energy usage of appliances, with circuit diagrams aiding engineers and electricians in device construction and repair. Circuit symbols differentiate electrical components, facilitating visual representation and identification within circuits. The included figure demonstrates a simple circuit, exemplifying the use of circuit symbols. 

A basic circuit diagram featuring symbols for a battery, ammeter, resistor, and voltmeter. 

Cell Circuit Symbol: Energizing Electric Circuits

In an electric circuit, the presence of an electric current requires a source of energy. Typically, a power source—often in the form of a cell or battery—supplies this energy. A cell transforms chemical potential energy into electric potential energy, enabling the flow of current through the circuit. A cell consists of two parallel lines, with one line being longer than the other. The longer line denotes the positive terminal, while the shorter line represents the negative terminal. Refer to the figure below to see the circuit symbol for a cell.

This symbol serves as a visual representation, indicating the presence of a cell as the energy source within a circuit.


The circuit symbol for a cell features a longer line, which specifically represents the positive terminal. 

Battery Circuit Symbol: Amplifying Electrical Energy

A battery, comprised of multiple cells connected in series within a circuit, offers a higher amount of electrical energy compared to a single cell. The circuit symbol for a battery is a repetition of the cell symbol, as illustrated in the figure below.


The circuit symbol for a battery 

Switch Circuit Symbol: Controlling Circuit Pathways 

In an electric circuit, a switch plays a crucial role in either breaking or joining the flow of current. When the switch is open, it interrupts the circuit, preventing the current from flowing. Conversely, when the switch is closed, it re-establishes the pathway, enabling the current to flow once more. The circuit symbols for an open switch and a closed switch are depicted in the figure below 

In this circuit diagram, the open and closed positions of a switch are represented.

Lamp Circuit Symbol: illuminating Pathways with Light

A lamp, also known as a bulb, serves as a source of light when an electric current passes through it. It can be utilized to test the presence of current in a circuit segment or to provide illumination. The circuit symbol representing a lamp consists of a cross enclosed within a circle, as exemplified in the figure below.


The circuit symbol for a lamp or bulb is represented by a simplified graphic depiction of the lamp.

Resistor Circuit Symbol: Regulating Current Flow

A resistor, a vital component in circuits, restricts the flow of electric current. A fixed resistor maintains a consistent resistance value (measured in ohms) and offers constant resistance to current flow. The circuit symbol representing a fixed resistor is a rectangular shape, as illustrated in the figure below.


The circuit symbol for a fixed resistor

Ammeter Circuit Symbol: Measuring Current with Precision

An ammeter is a specialized instrument employed to measure the current within an electric circuit. It is connected in series with the component or device to accurately gauge the current flow. The letter "A" enclosed within a circle serves as the circuit symbol for an ammeter, as shown in the figure below.


The symbol of an Ammeter

Voltmeter Circuit Symbol: Precision Measurement of Potential Difference

A voltmeter is a specialized instrument designed to measure the potential difference or voltage between two specific points within an electric circuit. To achieve accurate readings, it is connected in parallel between the two points of interest. The circuit symbol representing a voltmeter is the letter "V" enclosed within a circle, as exemplified in the figure below.


The symbol of a Voltmeter in a circuit

Variable Resistor Circuit Symbol: Adjusting Resistance for Current Control

A variable resistor, as the name suggests, is a type of resistor that allows for adjustable resistance. This feature enables it to control the current in a circuit. The circuit symbol for a variable resistor closely resembles that of a regular resistor, with the addition of an arrow passing through the rectangle. This symbol is illustrated in the figure below.


Symbol of a variable resistor

Fuse Circuit Symbol: Safeguarding Current Limits

A fuse serves as a protective device that melts when the current exceeds a specified threshold. This melting action opens the circuit, preventing further current flow. Various fuses possess distinct current ratings, ensuring they activate before reaching levels that could harm other components within the circuit. The circuit symbol for a fuse closely resembles that of a resistor, with a horizontal line passing through the rectangular shape. This symbol is illustrated in the figure below.


Symbol of a fuse in a circuit

Diode Circuit Symbol: Guiding Current Flow

A diode is a specialized component that permits current to flow in just one direction within a circuit. The diode blocks any attempts by the current to flow in the opposite direction. A diode appears as an arrow pointing in the direction of permitted current flow in a circuit symbol. The circuit symbol for a diode, demonstrating this characteristic, is exemplified in the figure below.


Symbol of Diod in a circuit

LED Circuit Symbol: Illuminating with Current Flow

A light-emitting diode (LED) is a diode that permits current to flow in only one direction. When current passes through it, the LED emits light. LEDs are commonly used for illumination purposes, and a single LED can also serve to indicate the presence of current in an electrical component. The circuit symbol for an LED resembles that of a diode, with outward-pointing arrows to signify the emission of light. This symbol is demonstrated in the figure below.


The symbol of light-emitting diode in a circuit

LDR Circuit Symbol: Adapting Resistance to Light Intensity

A light-dependent resistor (LDR) is a type of variable resistor that adjusts its resistance based on the intensity of incident light. LDRs exhibit higher resistance in low-intensity light conditions (dim light) and lower resistance in high-intensity light (bright light). The circuit symbol for an LDR resembles that of a resistor, with the rectangle enclosed by a circle. Inward-pointing arrows within the circle indicate incoming light. This symbol is exemplified in the figure below.


The symbol of light dependent resistor


Thermistor Circuit Symbol: Adapting Resistance to Temperature

A thermistor is a variable resistor that undergoes changes in resistance based on temperature variations. The commonly used type is the negative temperature coefficient (NTC) thermistor, which exhibits a decrease in resistance with increasing temperature and an increase in resistance with decreasing temperature. The circuit symbol for a thermistor resembles that of a resistor, but with an additional line passing through the rectangle. This symbol is depicted in the figure below.


The symbol of a Thermistor

Key Takeaways: Circuit Symbols


Circuit symbols play a crucial role in depicting the flow of current through different devices and appliances in an electric circuit. These symbols are represented in circuit diagrams, which are graphical representations of circuits.

A circuit diagram consists of various circuit symbols that are used to identify different components within the circuit. Each component is assigned a unique circuit symbol for easy identification.

To effectively work with circuit diagrams, it is essential to be able to recognize and draw circuit symbols for specific components. Some important circuit symbols to be familiar with include: