When we switch on a table lamp, its bulb glows, and when we switch on an electric fan, its blades rotate. We all know that these electrical devices work on electricity. Electricity is nothing but the flow of charge or current in an electric circuit. What causes the flow of current? The answer to this question is the potential difference across the terminals of an electrical device causes the current to flow through it. We can create this potential difference by connecting the electrical device with a source of energy like a cell. This simple arrangement of electrical components is called an electric circuit.

In simple terms, an Electrical circuit is a closed path of wires and electrical components which allows a current through it on the application of potential difference between two points in the path. In this article, you will learn about the definition, components, types of Electric circuits along with sample questions with solutions.

What is an Electric Circuit?

An electric circuit is a closed path in which an electric current can flow. A simple electric circuit comprises a source, a bulb or any other load and connecting wires. If terminals of a bulb are connected to the terminals of the source of electric current with the help of connecting wires, then a potential difference is set across its terminals. This causes the current to flow in the electric circuit, and the bulb glows. An electric circuit is said to be complete if all its parts are connected with wires made of conductors. If there is an insulator in the path of the circuit, it becomes incomplete.

Electric Circuit – Definition

An electric circuit is a network of various electrical components that provide a closed path for the current to flow.

An electric circuit consists of a source of electrical energy (electric cell or battery), a load that consumes electric power, connecting wires made of good electric conductors and a switch or key.

Components and Symbols used in an Electric Circuit

The components of an electric circuit are the elements that facilitate or control the flow of electric charge in a circuit. They all provide a conducting path for the current to flow through them. An electric circuit is made by connecting some of these electronic components. Some of the important electronic component and their symbols are as follows:

1. Electric cell: An electric cell is the source of electrical energy. It converts stored chemical energy into electrical energy. A simple dry cell consists of a zinc container whose base acts as the negative terminal, and a carbon rod is placed at its centre, which is fixed with a top made of brass. This brass top acts as the positive terminal of the cell. A dry cell used ammonium chloride as the electrolyte. The chemical reaction taking place in the cell drives the current in the electric circuit if the load is connected properly to its terminals. An electric circuit has two terminals. The positive terminal of the electric cell is represented by the longer line, and the negative is represented by the shorter line.

2. Battery: A combination of two or more electric cells is called a battery. It is a source of electrical energy. A typical dry cell provides a voltage of \({\rm{1}}{\rm{.5}}\,{\rm{V}}\), but if we connect two such cells end to end, we will get a battery that can provide a voltage of \(3\,{\rm{V}}\).

3. Bulb: A bulb is a device that produces light when an electric current passes through it. It consists of a filament made of tungsten (a high resistance wire). It heats up and glows when a current is passed through it.

4. Switch: A switch is a device that controls the flow of current through an electric circuit. It is a device that is used to make or break an electric circuit. If the switch is in the OFF position, the electric circuit will be open, and no current will pass through it. If the switch is in the ON position, it will allow current to pass through the electric circuit because the circuit will be closed.

5. Connecting wires: In an electric circuit, the connecting wires are always used to connect different circuit components together. These wires are made of materials that allow electricity to pass through them. For example, copper and aluminium. In an electric circuit, the wire joint and the wire crossing another wire are represented by the figures given below.

6. Resistance or resistor: Resistance is the opposition offered by a conductor to the flow of current through it. The device which does not allow current to pass through itly is known as a resistor.

7. Ammeter: The device which measures the amount of current flowing through an electric circuit is called an ammeter. The symbol of an ammeter is given below.

8. Voltmeter: The device which measures the amount of potential difference between any two points in an electric circuit is called a voltmeter.

Types of Electric Circuits and Electric Circuit Diagram

An electric circuit can be of two types depending upon their ability to allow the flow of current through them.z

1. Closed circuit: An electric circuit that is complete or has no breaks in between connecting wires is said to be a closed circuit. The switch in a closed circuit is in the ON position. There is no insulator present in the path of the current. A closed-circuit allows the current to pass through it.

2. Open circuit: An electric circuit that is broken or has an insulator in between the path of current is said to be an open circuit. The switch in an open circuit is in the OFF position. An open circuit does not allow the flow of current through it.

An electric circuit can be classified into two types depending upon the number of paths provided for the current to through it.

3. Series circuit: In a series circuit, there is only one path for the current to flow. In a series circuit, devices are connected end to end. The voltage across each device is different, but the same amount of current is received by them. This type of electric circuit offers greater resistance to the flow of current.

4. Parallel circuit: In a parallel circuit, there are two or more paths for the current to flow. All devices are connected such that the current through their common node is the same. In a parallel circuit connection, the voltage across each device is different. This type of circuit offers the least resistance and reduces the loss of energy.

Domestic Electric Circuit

Electricity is produced at electric power stations and transferred to our homes via transmission lines. This electricity reaches the electric boards that are fixed in our homes through the main power supply. There are three main wires via which the mains supply the electricity in our homes. One of these wires is called a live wire (or positive). The live wire has a red insulation cover, and the other wire is called neutral wire (or negative). This wire has a black insulation cover over it. A potential difference of \(220\,{\rm{V}}\) is maintained between these two wires. These wires pass into an electric meter through the main fuse, which protects appliances from overloading. Through the main switch, they are connected to the line wires, which supply electricity to separate circuits within the house. We are usually provided with two different circuits, one of \({\rm{15}}\,{\rm{A}}\) current rating, which is used for high power rating devices, and the other of \({\rm{5}}\,{\rm{A}}\) current which is used for low power rating devices. The earth wire, which is covered with green insulation, is used to protect us from electric shock in case of any current leakage. It is connected to the ground, and it provides a low resistance path for the current.

The domestic electric circuit is connected in the parallel arrangement because, in parallel circuit arrangement, each appliance receives the same potential difference. The failure of one device in the parallel arrangement will not affect the flow of current through other branches of the electric circuit. The equivalent resistance of the parallel circuit in domestic wiring will be the least, so it also reduces the loss of energy by the circuit.

Electric Circuit Simulator

An electric circuit simulator is a software tool that uses mathematical models to replicate the behaviour of electronic devices and electric circuits. It helps in understanding the function of an electric circuit by viewing and testing the circuit in a software program before creating the final circuit board.

Electric Circuit Analysis

Electric circuit analysis is a process of analyzing and finding all electrical quantities in a circuit of various electrical components. Those electric circuits which cannot be reduced by series-parallel combinations can be resolved by Kirchhoff’s law. The two main terms used in this law are as follows:

1. Junction: This is the point where three or more conductors meet.
2. Loop: This is any closed conducting path in an electric circuit.

Kirchhoff’s first law or current law \(({\rm{KCL}})\): This law states that the algebraic sum of all the currents meeting at a junction in an electric circuit must be zero.

\(\sum\limits_i {{I_i} = 0} \)

Kirchhoff’s second law or voltage law \(({\rm{KVL}})\): This law states that the algebraic sum of all the potential differences along a closed loop in a circuit must be zero.

\(\sum\limits_i {{V_i} = 0} \)

Solved Problems Based on Kirchhoff’s Law

Q.1. Find the current through each resistance of the circuit given below.

Sol: Let us assume the current \({I_1},\,{I_2}\) and \({I_3}\) are passing in the direction as shown in the figure.

Applying \({\rm{KCL}}\) at the junction \(X\), we get:

\({I_1} – {I_2} – {I_3} = 0\)

\( \Rightarrow {I_3} = {I_1} – {I_2}\)

Therefore, there are two unknown currents \({I_1}\) and \({I_2}\).

By applying \({\rm{KVL}}\) in the loop \(aXYba\) and \(XcdYX\) in the clockwise direction, we get:

Loop \(aXYba\):

\({\rm{5}}{I_1}{\rm{ }} + {\rm{ }}10{\rm{ }} + {\rm{ }}4{I_2}{\rm{ }} – {\rm{ }}6{\rm{ }} = {\rm{ }}0,\,\,\,\,……\left( 1 \right)\)

Loop \(XcdYX\):

\(10\left( {{I_1} – {I_2}} \right) + 8 – 4{I_2} – 10 = 0{\mkern 1mu} {\mkern 1mu} \,\,\,\,….\left( 2 \right)\)

From \((1)\), we get:

\(5{I_1}{\rm{ }} + {\rm{ }}4{I_2}{\rm{ }} + {\rm{ }}4{\rm{ }} = {\rm{ }}0\,\,\,\,\,…..\left( 3 \right)\)

From \((2)\), we get:

\(10{I_1}{\rm{ }} – {\rm{ }}14{I_2}{\rm{ }} – {\rm{ }}2{\rm{ }} = {\rm{ }}0\)
or \(5{I_1}{\rm{ }} – {\rm{ }}7{I_2}{\rm{ }} – {\rm{ }}1{\rm{ }} = {\rm{ }}0\,\,\,\,\,\,…\left( 4 \right)\)

Solving \((3)\) and \((4)\), we get:

\({I_1} =  – \frac{{24}}{{55}}A\)
\({I_2} =  – \frac{5}{{11}}A\)
\({I_3} = \frac{1}{{55}}A\)

Here, the negative sign indicated the direction of the current \({I_1}\) and \({I_2}\) are opposite to what we had assumed.

Q.2. In the circuit given below, assuming point \(A\) to be at zero potential, use Kirchhoff’s rule to find the potential at point \(B\).

Sol: By applying Kirchhoff’s current law at point \(D\), we get:

\({I_{DC}} = 2 – 1\)
\( \Rightarrow {I_{DC}} = 1A\)

Considering loop \(ACDB\) and applying \({\rm{KVL}},\) we get:

\({V_A} + 1 + (1 \times 2) – 2 – {V_B} = 0\)

It is given that \({V_A} = 0\)

\( \Rightarrow 0 + 1 + 2 – 2 = {V_B}\)
\( \Rightarrow {V_B} = 1\;{\rm{V}}\)

From this article, we can conclude that an electric circuit is a network of many electrical components that provides a closed path for the current to flow. Some examples of electrical components that are used in a simple electric circuit are electric cells, connecting wires, a switch and a load. An electric circuit may be open or closed. An open electric circuit does not allow electricity to pass through it, whereas a closed electric circuit allows electricity to pass through it.

Electric Circuit – FAQs

Q.1. What is an electric circuit and its types?
Ans: An electric circuit is a closed path through which a current can flow. An electric circuit is made of a source of electricity, connecting wires and load which utilizes the energy. The two types of electric circuits depending upon the number of paths for the current to flow are series circuit and parallel circuit.

Q.2. How can electric circuits be classified?
Ans: Electric circuits can be classified depending upon the number of paths they provide for the current to flow. There are two such types of electric circuits, namely series circuits and parallel circuits. Electric circuits can also be classified as open circuit and closed circuit depending upon their ability to allow the flow of current through them.

Q.3. When does an electric short circuit occur?
Ans: An electric short circuit occurs when the current flowing through the circuit abruptly increases. It may occur when live wire and neutral wire come in direct contact.

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