キルヒホッフの電圧の法則

Kirchhoff's Voltage Law (KVL) states that the algebraic sum of all voltages around a closed loop in a circuit equals zero. It is based on the principle of energy conservation, which means energy cannot be created or destroyed, only transferred or converted. This fundamental law ensures that the total voltage supplied in a loop equals the total voltage drop across all components.

Once you choose a loop direction (clockwise or counterclockwise), positive voltages are those where the negative terminal is encountered first as you traverse the loop. Negative voltages are those where the positive terminal is encountered first. The loop direction can start from any point in the circuit, but consistency in applying this sign convention is essential for correct KVL calculations.

The alternative form of KVL states that the sum of voltage drops across all components in a loop equals the sum of supplied voltages. This rearranged version is derived by applying KVL in a chosen direction and algebraically manipulating the terms. It provides a practical way to analyze circuits by equating the total voltage supplied by sources to the total voltage consumed by resistive elements.

In a series circuit with three LED lights each requiring three volts, KVL determines the required battery voltage by summing the voltage drops across all lights. Since the lights are in series, the total voltage drop is nine volts (3V + 3V + 3V). Therefore, the battery must supply nine volts to power all three lights, demonstrating how KVL relates supplied voltage to component voltage drops.

A circuit cannot contain two different voltages in parallel unless they are equal. In parallel connections, the same voltage is applied across all components, and any voltage discrepancy would violate the law of energy conservation and KVL. This constraint ensures that KVL remains valid and that energy is properly conserved throughout the circuit.

The loop direction determines the sign convention for voltages: whether a voltage is counted as positive or negative in the algebraic sum. Choosing clockwise or counterclockwise affects how you assign signs to each voltage based on terminal orientation. However, the final result—that the algebraic sum equals zero—remains consistent regardless of direction chosen, as long as signs are applied consistently.

KVL applies to all voltage sources in a circuit loop, whether they are independent and dependent sources or passive components. The law requires that the algebraic sum of voltages from all sources and voltage drops across resistive elements equals zero around any closed path. This makes KVL a universal tool for analyzing circuits containing various types of sources and elements.