ELECTRIC CIRCUIT ✅ Current, Voltage 💪 Kirchhoff's Voltage Law, Kirchhoff's Current Law | Middle School | 10th Grade

This comprehensive lesson covers the fundamentals of electrical circuits, detailing how to properly schematic them, understand the electrical quantities of intensity and voltage, and apply essential calculation laws such as the Law of Nodes and the Law of Loops.

An electrical circuit is fundamentally composed of at least one generator, which supplies the energy, and one receiver, which converts the electrical energy into another form, such as light or heat. Wires connect these elements, and an optional switch allows for manual control over the circuit's operation.

A crucial vocabulary term to retain is the dipole, which simply refers to any element within an electrical circuit structure that possesses exactly two connection terminals. This characteristic defines its role as either a source or a load within the network.

To easily and quickly represent an electrical circuit, standardized symbols are employed for every dipole. These symbols are universal, meaning individuals globally can interpret the schematic identically, facilitating clear technical communication across different regions.

When the schematic shows an illuminated lamp, it signifies that the switch is in the closed position, allowing current to circulate throughout the circuit. Conversely, if the switch is open, the current flow is interrupted, and the receiver ceases operation.

Electric current is defined as the directed movement of charged particles inside a conductor, a flow dictated by the generator. In metallic conductors, such as standard electrical wires, these moving particles are electrons, hence the term 'electron flow'.

Historically, scientists established a convention for the direction of current circulation; this is why the term 'conventional current direction' is used.

The conventional direction dictates that outside of a generator, the current travels from the positive terminal toward the negative terminal. On a schematic, this direction is clearly indicated by placing small arrows along the wires, but only if the current loop is confirmed to be closed.

The two primary types of electrical circuits are distinguished by how the dipoles are associated: either in series or in derivation (parallel). The visual structure of the schematic clearly differentiates these two configurations based on the number of current loops present.

In a series arrangement, all components share the same single path for current flow. Consequently, if one component breaks, the entire circuit path is broken, preventing any current from reaching the other receivers downstream.

Understanding the structure of circuits featuring derivations requires mastering three essential vocabulary terms: node, branch, and loop (maille). These concepts provide the necessary framework for accurately studying and quantifying electrical behavior within complex networks.

A node is specifically defined as any point within the circuit where a minimum of three electrical wires connect or separate. A branch is defined as the section of the circuit located strictly between two sequential nodes, representing a distinct path for current circulation.

A loop, or maille, is simply a closed path that can be traced through the circuit by following the wires without traversing the same point twice. This closed structure may or may not include the generator element itself.

Current intensity, symbolized by $I$, is the physical quantity characterizing the rate at which electrical charges pass through a specific cross-section per unit of time. Its standard unit of measure is the Ampere (A). On schematics, intensity is often denoted by small arrows matching the conventional current direction.

The measurement of electrical intensity is performed using an instrument called an ammeter. A critical rule dictates that the ammeter must always be connected in series at the precise location where the current flow rate needs to be determined. The standardized symbol for an ammeter is the letter 'A' enclosed in a circle.

If the instrument terminals are reversed, the measurement obtained will be the opposite (negative) of the actual intensity value considered.

The first law useful for intensity calculations is the Law of Unicity. This principle asserts that the current intensity value remains identical throughout every location within the confines of a single branch. The term 'unicity' emphasizes that the intensity is singular and unchanging along that specific path.

Because the intensity is constant across an entire branch, it is conventional practice on circuit diagrams to indicate the intensity direction with only a single arrow marking for that specific branch segment.

The second law concerning intensity is the Law of Nodes, which governs how current splits or merges at junctions. This law states that the total sum of all current intensities flowing into a specific node must be exactly equal to the total sum of all current intensities flowing out of that node.

When examining a node where intensity $I_G$ arrives and intensities $I_L$ and $I_M$ depart, the mathematical expression derived from this law is $I_G = I_L + I_M$. This equality holds true for every node present in the circuit network.

Electric voltage, denoted by $U$, is a physical quantity that characterizes the electrical potential difference existing between two distinct points within a circuit, and it is quantified in Volts (V). To represent voltage on a schematic, a large directional arrow is drawn across the terminals of the component in question.

When drawing voltage arrows, adherence to the Generator-Receiver Convention is mandatory. For any dipole acting as a generator, the voltage arrow must be oriented in the exact same direction as the conventional current. Conversely, for receiver dipoles, such as lamps or motors, the voltage arrow must point in the direction opposite to the conventional current flow.

Voltage measurement requires a voltmeter, which must always be connected in derivation (parallel) across the two points defining the potential difference. This contrasts with the ammeter, as the voltmeter needs to measure the electrical state at two separate locations simultaneously to calculate the difference. The standardized symbol for a voltmeter is a 'V' inside a circle.

The first law applicable to voltage calculations is the Law of Unicity of Voltage. This rule stipulates that the voltage measured across any branches that are connected in parallel (in derivation) must be identical. Identifying these parallel relationships is simplified by correctly locating the circuit nodes.

If a generator provides a voltage $U_G$, and this voltage is distributed across a lamp ($U_L$) and a motor ($U_M$) connected in parallel, the law dictates that $U_G = U_L$ and $U_L = U_M$, meaning all parallel components experience the same electrical potential difference.

The Law of Loops, also known as the Law of Voltage Additivity, is frequently employed because it allows for the verification and derivation of voltage equalities. When traversing any single, oriented loop within the circuit, the algebraic sum of all encountered voltages must equal zero volts.

To orient a loop, a specific direction of traversal must be defined, often marked by letters on the circuit diagram. When counting the voltages, any voltage arrow pointing in the same direction as the defined loop traversal is counted positively, while arrows opposing the traversal direction are counted negatively.

Effective voltage calculation relies on a strict sequence: first, establish the conventional current direction; second, draw all voltage arrows respecting generator/receiver conventions; third, define the orientation for the loop being analyzed; and finally, write the resulting algebraic equality by summing the terms around the loop.

Successful completion of this review confirms mastery over fundamental concepts required for studying and analyzing electrical circuits. Continued practice through exercises is highly recommended to solidify understanding of intensity, voltage, and Kirchhoff's laws.