## What is an electric circuit?

An electrical circuit or electrical network is a pre-determined pathway to make the electrons flow in the desired direction. The flow of electrons will set up a current flow in the circuit. Normally, the flow of electrical current is opposite to the flow of electrons. An electron is a fundamental sub-atomic particle of an atom possessing a negative charge. To initiate the flow of current and achieve the desired output, the electrical circuit should necessarily be composed of closed pathways. The pathways are made-up of good conductors of electricity such as aluminium and copper.

The flow of electrical current in a circuit to achieve desired response is accomplished by fixing different electrical components. The components are discrete devices that affect electrons and their related electric fields, which directly change electric current properties. Some of the components used in an electric circuit are transistors, resistors, capacitors, inductor coils, power supply units like a battery, electromagnets, transformers, etc.

## Classification of electrical network or circuit

### Active electrical circuit

Active electrical circuits consist of at least one voltage or power source as its prime component, which can continuously power the circuit. The voltage source can be an AC or DC. A battery or a generator may also act as a voltage source. These voltage sources are preferably known as sources of electromotive force (EMF). These voltage sources induce a power gain in the circuit that controls the flow of current.

Any electrical circuit which does not contain any voltage sources is termed a passive source, they only contain resistors and capacitors.

### Linear electrical circuit

If the electric current flowing in the circuit obeys the principle of superposition, the circuit is known as a linear electrical circuit. According to the theory of superposition, the response of an electrical circuit in terms of current and voltage, due to the presence of multiple independent sources, exactly equals the arithmetic summation of voltages of the individual sources. Passive circuits are generally linear circuits.

### Lumped electrical circuit

If in an electrical circuit, the components' positions are finitely fixed at a specific location or their positions are lumped, the circuit is known as a lumped electrical circuit.

## Electric circuit components

### Active circuit components

The active circuit components comprise diodes, transistors, integrated circuits (ICs), and thermionic valves. These components mainly form the basic electronic components of a simple circuit.

• Diodes: The diodes form the basic element in a rectifier system that converts AC to DC voltage.
• Transistor: The transistor forms the basic element in an electrical as well as an electronic circuit. It is a semiconductor device that performs the task of switching electric current in a circuit. A transistor has three pins namely the emitter, collector, and base.
• ICs: ICs comprise a cluster of electronic circuits in a small flat piece of semiconductor material known as a chip. They greatly reduce the size of an electronic device.
• Thermionic valves: Thermionic values are also known as vacuum tubes, the very first component in the initial revolution of computers. These devices accelerate electrons from cathode to anode by an electric field. These are used for electric current amplification and rectification.

### Passive circuit components

#### Resistor

Resistors are the bi-terminal devices that are used to resist the flow of electric current in an electric circuit. Besides providing resistance, a resistor is also used to regulate the signal levels, voltage dividing, biasing components, and terminate the flow of current in transmission lines. There are generally two types of resistors used in a circuit, fixed resistor, which has fixed resistance value, and variable resistors or rheostats. The resistance values in a rheostat can be varied according to needs.

#### Capacitor

The capacitor is an electric component that stores electric charge and essentially has two terminals connected to two plates. The effect of a capacitor is termed capacitance. Capacitance is the ratio between the magnitude of the charge stored in the conductive plates of the capacitor and the difference in electric potential between the two plates.

#### Inductor

An inductor is an electric component that works on the principle of Faraday's law of induction and follows Lenz's law. It is a coil through which electric current flows. A change in the current induces a magnetic field which induces an EMF, the nature of the EMF is such that it opposes the electric current. Hence, an inductor opposes any changes in electric current. An inductor is characterized by inductance. Inductance is the ratio between voltage and current change.

## Measuring electric parameters

### Ammeter

An ammeter is a device that is used to measure the amount of current flowing in a circuit. The ammeter measures electric current in the units of Ampere, in the honor of French physicist Andre Marie Ampere.

### Voltmeter

A voltmeter is a device whose purpose is to measure the potential difference between two terminals of a component. The readings are in volts.

### Multimeter

A multimeter is an all-around device that is used to measure signal continuity, current, voltage, and resistance values.

## Context and Applications

The topic is taught in many undergraduate and postgraduate degree courses like:

• Bachelors of Technology (Instrumentation Engineering)
• Bachelors of Technology (Electrical Engineering)
• Bachelors of Technology (Electrical and Electronics Engineering)
• Bachelors of Technology (Electronics Engineering)
• Bachelors of Technology (Mechanical Engineering)

## Practice Problems

Q 1. Which of the following wire material can be used in an electrical circuit?

1. Copper wire
2. Aluminum wire
3. Both a and b
4. None of these

Explanation: Both copper wire and aluminum wires can be used in an electrical circuit as both of these wires are made up of good conductors of electricity.

Q 2. In the honor of which of the following physicists does the unit of current adopt?

1. Gustav Robert Kirchhoff
2. Andre Marie Ampere
4. Heinrich Friedrich Emil Lenz

Explanation: The unit of electric current is Ampere, named in the honor of French physicist Andre Marie Ampere.

Q 3. Which of the following electric components opposes any changes in electric current in a circuit?

1. Capacitor
2. Resistor
3. Electromagnet
4. Inductance

Explanation: An inductor opposes any changes in the electric current flowing in an electric circuit.

Q 4. Which of the following is the ratio between the voltage and rate of electric current change?

1. Impedance
2. Inductance
3. Resistance
4. Capacitance

Explanation: Inductance is the ratio between voltage and rate of electric current change.

Q 5. Which of the following electric circuits contains a battery?

1. Active circuit
2. Passive circuit
3. Linear circuit
4. None of these

Explanation: Active circuits are those, which essentially have a power source like a battery.

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