An Introduction to Electric Current
An electric circuit is a path through which electric current flows. An electric circuit can also be a closed path (in which the ends are joined), thereby making it a loop. The flow of electric current is possible because of the closed circuit. An electric circuit can also be an open circuit in which the flow of electrons is cut because the circuit is broken. Electric current doesn't flow in an open circuit.
It is important to know about the basic parts of an electric circuit. A simple electric circuit contains a source, a switch, a load, and a conductor. The functions of these parts are:
● Cell: It is used as a source to supply electric current.
● Load: It is a resistor. It is basically a light bulb, which glows when the circuit is turned on.
● Conductors: Copper wires are used as conductors with no insulation. One end of the wire carries current from the power source to the load and the other end from the power source.
● Switch: It is a part of the circuit that controls the supply of current in the circuit. It is used to open or close the circuit.
Electric current and voltage are the two basic features of an electric circuit. Electric circuit analysis is a process in which current and voltage are determined in any element of the electric circuit.
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The above figure represents a simple electric circuit containing:
A battery of 30 V (voltage)
A carbon resistor of 5 kΩ (resistance)
Due to the complete circuit, current I flows through the circuit, and a potential drop of V volts is developed across the resistor.
Types of Electric Circuits
There are two types of electric circuits.
Series circuit.
Parallel circuit.
Series Circuit
In a series circuit, there is only one path for the flow of electrons. The entire circuit is closed or open at the same time. No current flow in the circuit in case of a circuit break because the entire circuit is open; this is the major disadvantage of a series circuit. For example, if many light bulbs are connected in a series circuit, then if one light bulb goes out, the others will also turn off.
Parallel Circuit
In a parallel type of electric circuit, different parts of the circuit are connected across different branches. Hence, electron flow occurs in several parts. If in one path a circuit break occurs, electric current still flows in other paths. Household wiring of appliances are based on parallel circuits, so if one light bulb goes down, the other will still flow.
Domestic Electric Circuit
The above figure represents the domestic circuit diagram.
The electric power that we receive in our houses is by the main supply, commonly called mains.
It is supplied by either overhead cables or by underground cables.
There are 3 types of wires in domestic circuits and are Earth Wire, Live Wire, and Neutral Wire.
Earth Wire: The earth wire is generally green in color. It is connected with a metal plate buried in the ground near the house, to provide safety for the gadgets and appliances which have a metallic body. When a charge leak occurs in the metallic body, the charges are transmitted to the ground to prevent shocks and damage.
Live Wire: It is the positive conductor or wire which is generally red in colour.
Neutral Wire: It is the negative conductor or wire which is generally black in colour.
The potential difference (or voltage) which is supplied in our country is 220V.
The electric current of our house is first passed through a circuit called a Fuse. If any high voltage, overloading, voltage fluctuation or short circuit occurs, the fuse melts thereby restricting the current supply and preventing the high voltage from reaching the electric appliances.
These wires are passed to different electric appliances of the house through the meter board.
Generally, 2 types of electric circuits are used for household use:
15 A: Appliances that have higher power ratings. ( like geysers, ACs, refrigerators)
5 A: Appliances that have lower power ratings. ( like TV, fans, bulbs)
Basic Circuit Parts
As mentioned on top of, a circuit may be a hub of parts connected to every different. Circuit parts area units are classified into 2 parts, active or passive parts, in step with their capability to make energy.
Active Circuit parts
Active parts unit those parts that may generate energy on their own. for instance diodes, amplifiers, batteries, and generators. The supply parts area unit is the foremost crucial active part Of the associate electrical device.
Sources sort of a voltage or current area unit of 2 varieties that area unit freelance sources and Dependent sources. An electric battery is an associate freelance supply that has a continuing voltage to the circuit, regardless of this that's passing through the terminals.
A semiconductor unit may be a supply that provides current to the circuit, semiconductor unit depends upon the facility applied thereto.
Passive circuit parts
Elements that may manage the flow of electrons through them are a unit referred to as Passive parts. they're capable of either increasing or decreasing the voltage. Below are some samples of passive parts.
Resistor
For a linear circuit, an electrical device opposes the flow of current through. Ohm’s law comes into the image, which states that voltage across the electrical device is directly proportional to this passing through it, the proportional constant being the resistance thereto.
Inductor
The associate electrical device helps to store energy within the variety of the magnetic force field in order that the voltage across the associate electrical device is capable of the constant amendment of current passing through it.
Capacitor
An electrical condenser helps to store energy within the variety of the electric field conjointly, the voltage across an electrical condenser is capable of the charge.
What Area Unit associates an Electric Circuit and a Brief Circuit?
Short
The affiliation between 2 conductors with low resistance in an electrical circuit is named a brief circuit. you will have seen sparks and smoke thanks to the warmth made, that's due to a brief circuit. Short circuits generate additional heat.
There are a variety of reasons for a brief circuit to occur in that area, some loose connections, defective insulation, faulty wires or chews by animals, and out-of-date electrical appliances. to forestall such dangerous situations, the simplest and normally used technique to forestall damages employing a fuse or an electrical fuse that stops short circuits.
Open Circuit
An interruption within the electrical device is the main reason behind the associated electric circuit. Unconnected parts {in a|during a|in associate exceedingly|in a very} circuit produces an electric circuit.
Circuit Protection
The addition of a weak link inside the associated electrical device is named circuit protection. The explanation behind the installation of a weak link is to forestall injury thanks to short circuits, and an associated extreme quantity of temperature. A fuse, switch logic gate breaker may be a circuit protection device. Studies show that thanks to circuit protection, such damages were reduced.
Electrical Safety
Studies show that quite 100 individuals die per annum thanks to electrical shock in their workplaces and around sixty individuals die per annum once obtaining an electrical shock from varied power tools and cables.
The reason to bring this up to you is to form individuals conscious of the security precautions and thumb rules that an area unit imagined being followed once operating with electricity. Electricity may be very dangerous to trot out and untrustiness will value your life. It's common that individuals hump their phones on a charge, blocked in sockets. There are some WHO even place their phones on charge and so hump earphones in their ears. To heaps of individuals this won’t be an enormous deal, but, over the past few years, we've noticed and detected such a large amount of youth dying simply because of their cognitive content.
Precautions while using Electric Circuits
Always use good quality wires which have proper insulation and thickness, for household wiring. Install products like plugs, switches, and sockets that have an ISI mark in them for better use of electrical appliances.
The connections of the wires should be tight and completely insulated.
You should always switch off the mains supply before starting any repair work of the electric circuit.
If any short circuit or shock occurs, switch off the main supply at first. Then try to totally insulate the person who has received an electric shock. Do not touch him directly.
While earthing or installing a fuse for the household electric circuits, you should take precautions.
FAQs on Electric Circuit
1. What is meant by an electric circuit and how does it function in a closed path?
An electric circuit is a closed path through which electric current flows from the power source, passes through various components such as resistors, and returns to the source. Current flows only when the circuit is complete and closed, allowing the movement of electrons from the negative to the positive terminal.
2. What are the main components of a basic electric circuit as required for CBSE Class 12 Physics?
A basic electric circuit comprises the following main components:
- Source of energy (e.g., battery or cell)
- Conducting wires (usually copper)
- Load (such as a resistor or bulb)
- Switch (to open or close the circuit)
3. How are series and parallel circuits different in terms of structure and function?
In a series circuit, all components are connected end-to-end, providing only one path for current flow. If one component fails, the entire circuit stops working. In a parallel circuit, components are connected across common points, allowing current to flow through multiple paths. If one component fails, others can still operate.
4. Why is using a fuse essential in domestic electric circuits?
A fuse safeguards electric circuits by melting and breaking the circuit if there is excess current flow due to short-circuiting or overloading. This prevents damage to appliances and reduces the risk of electrical fires and shocks.
5. Explain the functions of earth, live, and neutral wires in a household electric circuit as per CBSE standards.
The earth wire provides safety by directing leakage current to the ground, the live wire (red) carries current to appliances, and the neutral wire (black) completes the circuit by carrying current away. In India, the live wire is typically at 220 volts, and the neutral wire is at 0 volts.
6. What happens to the potential difference across a resistor when electric current flows through it?
When electric current passes through a resistor, a potential difference develops across its ends according to Ohm's Law (V = IR). This means the voltage across the resistor is proportional to the current passing through it and its resistance value.
7. How does a short circuit occur, and what are the risks associated with it?
A short circuit happens when two conductors in an electric circuit come into direct contact, bypassing the load and causing excessive current flow. This can lead to overheating, sparks, smoke, damage to circuits, and even electrical fires.
8. What are active and passive circuit elements? Give examples for each.
Active elements can supply energy to the circuit, such as batteries, generators, and amplifiers. Passive elements cannot generate energy but can store or dissipate it, examples include resistors, capacitors, and inductors.
9. How is current in a series circuit calculated using Ohm's Law for Class 12 board exams?
In a series circuit, total resistance is the sum of the resistances (Rtotal = R1 + R2 + ...). Current (I) is calculated as I = V / Rtotal, where V is the total voltage applied to the circuit.
10. What safety measures should be followed during repair and maintenance of electric circuits at home?
Always switch off the main supply before starting repairs. Use good quality wires with proper insulation, ensure all connections are tight, and avoid direct contact with wires or a person who has received an electric shock. Install components with ISI marks for reliability and safety.
11. Why does current not flow in an open circuit?
In an open circuit, the continuous path required for electric current is broken. As a result, electrons cannot flow, and no current is observed in the circuit.
12. How does the concept of potential drop relate to the arrangement of resistors in an electric circuit?
The potential drop across resistors in an electric circuit is determined by their values and arrangement. In series, the drop is divided among all resistors proportionally. In parallel, each resistor experiences the same potential difference as the source.
13. What is the conventional direction of electric current, and how does it compare to the actual flow of electrons?
The conventional direction of electric current is from the positive terminal to the negative terminal of the power source, opposite to the actual flow of electrons, which move from negative to positive.
14. How should one approach solving circuit diagram questions in the 2025–26 CBSE Physics board exams?
First, identify and label all components. Apply Ohm’s Law and circuit laws (Kirchhoff’s Laws) as needed. Calculate total resistance or equivalent values before finding current, voltage, or power across each element. Always check units and steps as per CBSE marking scheme.
15. What are some common misconceptions students have about electric circuits?
Common misconceptions include:
- Thinking current is ‘used up’ as it passes through components (it is not; it remains the same in series circuits).
- Confusing voltage with current direction.
- Assuming a broken component in a parallel circuit stops all devices (in parallel circuits, other branches work independently).
