The sum of the voltages over any closed loop is equal to 0V. This rule is known as Kirchhoff's Voltage Law (KVL) and is a fundamental principle in electrical circuit analysis. KVL states that the algebraic sum of all the voltages around any closed loop in a circuit is zero.

Explanation of Kirchhoff's Voltage Law (KVL):
- Key Point: Kirchhoff's Voltage Law (KVL) states that the sum of the voltage rises is equal to the sum of the voltage drops in any closed loop in a circuit.
- Closed Loop: A closed loop is a path that starts and ends at the same point, forming a closed circuit.
- Voltage Rises: Voltage rises occur when moving from the negative terminal of a component to its positive terminal. This is usually associated with voltage sources such as batteries or power supplies.
- Voltage Drops: Voltage drops occur when moving from the positive terminal of a component to its negative terminal. This is usually associated with resistors, capacitors, and other passive elements in a circuit.

Example:
Consider a simple circuit consisting of a battery and a resistor connected in series. Let's assume the battery has a voltage of 5V, and the resistor has a resistance of 10Ω.

- The voltage across the battery is 5V, and it is considered a voltage rise because we are moving from its negative terminal to its positive terminal.
- The voltage across the resistor is determined using Ohm's law: V = IR. Given that the current flowing through the resistor is I = 0.5A, the voltage drop across the resistor is V = (0.5A)(10Ω) = 5V.
- According to KVL, the sum of the voltage rises and drops in the closed loop (battery-resistor-battery) must be zero. Therefore, the voltage rise of 5V across the battery must be balanced by the voltage drop of 5V across the resistor, resulting in a total voltage of 0V.

Conclusion:
Kirchhoff's Voltage Law (KVL) is a fundamental principle that states the sum of the voltages around any closed loop in a circuit is zero. This law is crucial in analyzing and solving electrical circuits, allowing us to determine the relationships between voltages and currents in different components.