What is Kirchhoff’s Law | Definition, Examples, Diagrams

In this article we will read about What is Kirchhoff’s Laws in the chapter on Physics. This rule is very important. What is Kirchhoff’s law? Questions are asked in class 10 and class 12 and also in other competitive exams.

What is Kirchhoff’s law, first law is of current and second of voltage and when it is given junction or junction, loop, branch or branch. To understand Kirchhoff’s first law, first you have to understand three things, junction and branch. You can read the definition of all of them below.

Kirchhoff was a German physicist who, in 1842, scientist Kirchhoff was doing some electrical experiments. Scientist Kirchhoff gave two rules for the analysis of electric circuits, which are applicable in all types of electrical networks, these laws show the conservation of charge and energy, with the help of which we can set up electric nets in any configuration. In fact, Kirchhoff’s first and second laws are based on Ohm’s law or it can be said that it is an application of Ohm’s law designed to solve complex circuits. .

What is a branch, understand for Kirchhoff’s law, that part of an electric circuit where the value of current remains constant, that part is called a branch, the point of an electric circuit where three or more branches meet is called a junction, it is called a node. And also called junction.

What is Kirchhoff’s Laws

In electrical circuits, sometimes many resistors and cells are connected in a complex manner. The formulas we have derived earlier for series and side connections are not always sufficient for all electric currents and potential differences in a circuit. Two laws, which are called Kirkhoff’s laws. Different types of DC A scientist named Kirchhoff has established two rules for circuits, they are as follows

Kirchhoff’s first Current law

(i) Current Law: “The sum of the currents going towards a joint of conductors is equal to the sum of the currents going away from the union.” If the currents leading to the confluence are i1, i2 and the currents going out from the confluence are i₃, i₄, i₅, then

i₁ + I₂ = i₃ + i₄ + i₅

Kirchhoff’s Laws

In other words, the sum of the entering currents at any point (Node) of the circuit is equal to the sum of the output currents. That is, the algebraic sum of currents at any node is zero.

∑ i = 0(zero) ……(1)

i₁ + i₂ – i₃ – i₄ – i₅ = 0  ……(2)
i₁ + I₂ = i₃ + i₄ + i₅  ……(3)

Kirchhoff’s first law can also be written as – “The sum of all the electric currents entering the junction of an electric circuit is equal to the sum of all the electric currents coming out of this junction.”

Thus it is clear from the equation that the sum of all the currents coming towards a junction is equal to the sum of all the currents going away from that junction. In other words, when a constant current flows through a circuit, charge is neither accumulated nor removed from any junction in the circuit, i.e. Kirchhoff’s law is based on the principle of conservation of charge, it is called Kirchhoff’s current. it is said. Also called rule.

Kirchhoff’s second voltage law

(ii) Voltage law: The algebraic sum of the inverse forces applied in a closed circuit is equal to the algebraic sum of the products of the currents flowing in its branches and the resistances of those branches. In other words

∑IR = ∑E  ……(4)

In other words, Kirchhoff’s potential law is applied inside a loop, in which the carrying force applied in any closed circuit is equal to the algebraic sum of the potentials of the components present in the circuit, that is, the algebraic sum of the potential differences of the components in a closed circuit is zero. Kirchhoff’s law is used to determine the value of current in mixed type circuits. Kirchhoff’s second law is based on conservation of energy, it is also called Kirchhoff’s law of voltage.

The following rules are kept in mind while making calculations-

  • When we move in the direction of current, we take the product of current and its corresponding resistance to be positive and when we move in the opposite direction of current, we take the product of current and its corresponding resistance to be negative.
  • In the electrolyte of the cell, the electromotive force is considered negative when moving from the negative electrode to the positive electrode and is considered positive when moving from the positive to the negative electrode.

Kirchhoff’s Laws

Let us understand this with an example, suppose there is an electric circuit in the given figure, in which current is flowing through external resistance R by connecting cells having E₁ or E₂ respectively in parallel and the internal resistance of these cells is r₁V.

respectively. r₂ Now if the current drawn from these cells is I₁ or I₂ respectively and if the current through the external resistance R is I₃, then according to Kirchhoff’s first law at the junction D

I₃ = I₁ + I₂  ……(5)

Now in the circuit ADCBA according to Kirchhoff’s second law,

I₁r₁ − I₂r₂ − E₁ + E₂ = 0  ……(6)

and in the circuit CDEFC,

I₂r₂ + (I₁ + I₂)R − E₂  = 0  ……(7)

According to Kirchhoff’s second law in a circuit AEFBA,

(I₁ + I₂)R + I₁r₁ – E₁ = 0  ……(8)

On solving the above equation (6) or (7)

The values ​​of I₁ or I₂ are obtained.

Read More-

Quetions- Find the value of i3 in the given circuit –

Kirchhoff’s Laws

SOL. Apply Kirchhoff’s law of current at the given node.

i1 + i2 = i3 + i4  replace the known value

2 + 9 = i3 + 4 Solve for i3  i3 = 7 A

Frequently Asked Questions

Question-1 On what quantity is the conservation of Kirchhoff’s second law for an electric circuit based?

Answer: Law of Conservation of Energy

Question-2 What is the law of conservation of charge? / What is the Law of Conservation of Charges in Hindi?

Answer- You can neither create nor destroy charge, this charge is inherently free and can be transferred from one place to another.

Question-3 What is loop? / What is loop in Hindi?

Ans- A closed circuit in which no element/element occurs more than once.

Q-4 What is branch? / What is branch in Hindi?

The north-branch connects the two junctions and the value of the current remains unchanged.

Question-5 What is a junction / junction? / What is a junction called in Hindi?

Answer- The point where three or more paths meet. It is called joint/junction/node.


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