Kirchhoffs Rules – Class 12 | Chapter – 3 | Physics Short Notes Series PDF for NEET & JEE

Kirchhoffs Rules: Kirchhoff’s laws are two fundamental rules in electrical circuit analysis that describe the behavior of electric circuits. Kirchhoff’s first law goes by several names as Kirchhoff’s Current Law (KCL), Kirchhoff’s Junction Rule, Kirchhoff’s point rule, Kirchhoff’s nodal rule. It is an application of the principle of conservation of electric charge. The law states that at any circuit junction, the sum of the currents flowing into and out of that junction are equal.

Laws of Kirchhoffs Rules

• Kirchhoff’s First Law (Kirchhoff’s Current Law or KCL): This law states that the total current entering a junction in a circuit must equal the total current leaving the junction. Mathematically, this can be expressed as the sum of the currents flowing into a junction being equal to zero.

• Kirchhoff’s Second Law (Kirchhoff’s Voltage Law or KVL): This law states that the total voltage around any closed loop in a circuit must be equal to zero. Mathematically, this can be expressed as the sum of the voltage drops around a closed loop being equal to the total voltage applied to the loop.

These laws are used to analyze and understand the behavior of electric circuits, including determining the currents and voltages at various points in the circuit, solving for unknown values in complex circuits, and finding the overall impedance of a circuit.

Kirchhoff’s First Law or Kirchhoff’s Current Law

Kirchhoff’s First Law, also known as Kirchhoff’s Current Law (KCL), states that the total current entering a junction in a circuit must equal the total current leaving the junction. In other words, the sum of the currents flowing into a junction must be equal to zero.

This law is based on the conservation of charge principle, which states that charge cannot be created or destroyed, but can only be transferred from one place to another. As a result, the amount of charge flowing into a junction must equal the amount of charge flowing out of the junction.

KCL is a crucial law in electrical circuit analysis and is used to determine the current flowing through each component in a circuit, as well as to solve for unknown currents in complex circuits. By using KCL in conjunction with Kirchhoff’s Second Law (Kirchhoff’s Voltage Law), the behavior of a circuit can be fully analyzed and understood.

Kirchhoff’s Second Law or Kirchhoff’s Voltage Law

Kirchhoff’s Second Law, also known as Kirchhoff’s Voltage Law (KVL), states that the total voltage around any closed loop in a circuit must be equal to zero. This law is based on the concept of energy conservation, which states that energy cannot be created or destroyed, but can only be transferred from one form to another.

In a closed loop circuit, the voltage applied to the loop is equal to the sum of the voltage drops around the loop. This can be expressed mathematically as the sum of the voltages around the loop being equal to zero:

ΣV = Vapplied + V1 + V2 + … + Vn = 0

where ΣV is the sum of the voltages around the loop, Vapplied is the applied voltage, and V1, V2, …, Vn are the voltage drops across the components in the circuit.

KVL is used to analyze the behavior of electric circuits, including determining the voltages at various points in the circuit, solving for unknown values in complex circuits, and finding the overall impedance of a circuit.

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