Assertion (A) : Transformer is useful for stepping up or stepping down voltages. Reason (R) : Transformer is a device used in D.C. circuits. In the context of the above two statements, which one of the following is correct ?

1. Understanding Electric Current: AC vs. DC (basic)

At its most fundamental level, electric current is the stream of electrons moving through a conductor, much like water flowing through a pipe Science, Class X (NCERT 2025 ed.), Electricity, p.192. However, not all electricity flows the same way. Depending on how those electrons move, we classify current into two types: Direct Current (DC) and Alternating Current (AC).

Direct Current (DC) is straightforward—the electrons flow in a single, constant direction from the source to the device. Think of it as a one-way street. This type of electricity is typically generated by cells and batteries Science-Class VII, NCERT(Revised ed 2025), Electricity: Circuits and their Components, p.36. Because DC provides a steady, unchanging voltage, it is ideal for small electronic devices like your smartphone, flashlight, or laptop. Interestingly, while solar panels and batteries produce DC, many of our modern needs require converting that DC into AC using a device called an inverter Environment, Shankar IAS Academy (ed 10th), Renewable Energy, p.288.

Alternating Current (AC), on the other hand, is like a pendulum; the electrons constantly reverse their direction of flow at regular intervals. In India, the AC electricity supplied to our homes reverses its direction 100 times every second, which we call a frequency of 50 Hz Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206. We use AC for our national power grids because it can be easily transported over long distances with minimal energy loss. In a typical household setup, you will find three wires: the Live wire (red), the Neutral wire (black), and the Earth wire (green) Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206.

Feature	Direct Current (DC)	Alternating Current (AC)
Direction	Constant (One direction)	Periodic Reversals
Source	Batteries, Solar Cells	Power Plants, Wall Sockets
Frequency	Zero	50 Hz (in India)

Sources: Science, Class X (NCERT 2025 ed.), Electricity, p.192; Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206; Science-Class VII, NCERT(Revised ed 2025), Electricity: Circuits and their Components, p.36; Environment, Shankar IAS Academy (ed 10th), Renewable Energy, p.288

2. Magnetic Effects of Electric Current (basic)

In 1820, a Danish professor named Hans Christian Oersted accidentally changed the course of physics. While performing a demonstration, he noticed that a compass needle deflected when placed near a wire carrying an electric current Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.195. This proved a fundamental law of nature: moving electric charges (current) generate a magnetic field. Before this discovery, electricity and magnetism were thought to be completely separate forces. This interaction is why we call the study Electromagnetism, a principle that powers everything from the simple doorbell to massive industrial motors. The pattern of the magnetic field produced depends entirely on the shape of the conductor. For a straight metallic wire, the magnetic field lines form a series of concentric circles centered on the wire Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206. If you increase the current, the field becomes stronger, and the field lines appear closer together. Conversely, as you move further away from the wire, the magnetic field strength decreases, and the circles become larger and more spread out. When we change the shape of the wire into a loop or a coil (called a solenoid), these individual circular fields add up to create a much stronger and more useful magnetic field, similar to that of a bar magnet. This allows us to create electromagnets by wrapping a coil of wire around a soft iron core, which concentrates the magnetic lines of force Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206.

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.195; Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206

3. Faraday’s Law of Electromagnetic Induction (intermediate)

In our previous steps, we saw how an electric current creates a magnetic field. Faraday’s Law of Electromagnetic Induction is the brilliant "reverse" of that discovery. In 1831, Michael Faraday demonstrated that magnetism can actually produce electricity, provided there is motion or change involved. This principle is the backbone of almost every modern power plant and electrical transformer.

To understand this, imagine a loop of wire and a bar magnet. If the magnet sits still inside the loop, nothing happens. However, if you move the magnet quickly toward or away from the loop, a current momentarily flows through the wire. This happens because of a change in magnetic flux (the total magnetic field passing through the loop). Faraday’s Law states that the induced Electromotive Force (EMF), or voltage, is directly proportional to the rate of change of this magnetic flux. As noted in Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.207, we can determine the direction of this induced current using rules like Fleming’s Right-Hand Rule.

A crucial takeaway for the UPSC is why this Law necessitates Alternating Current (AC) for devices like transformers. A transformer consists of two coils. If we pass a steady Direct Current (DC) through the first coil, it creates a constant magnetic field. Since the field isn't changing, the flux isn't changing, and thus no voltage is induced in the second coil. However, AC is constantly rising and falling in value; this creates a continuously varying magnetic field, which satisfies Faraday's Law and allows electricity to be "transformed" from one circuit to another without any physical movement of the coils.

Scenario	Magnetic Flux Status	Induced Current?
Stationary Magnet in Coil	Constant (No change)	No
Moving Magnet in/out of Coil	Changing	Yes
Steady DC in a Transformer	Constant (No change)	No
Fluctuating AC in a Transformer	Changing continuously	Yes

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.207

4. Power Generation and Grid Transmission (intermediate)

To understand how power reaches our homes, we must look at the journey from the power plant to the socket. In India, the energy landscape is diverse: we are the **world's third-largest producer and consumer** of electricity Indian Economy, Nitin Singhania, p.448. Our power comes from a mix of sources, predominantly **thermal energy (63%)**, followed by **Renewable Energy (23%)**, and **hydroelectricity (12%)** Indian Economy, Nitin Singhania, p.448. Because these plants are often located far from cities, the electricity must be transported efficiently over vast distances, sometimes exceeding 1600 km Certificate Physical and Human Geography, GC Leong, p.273.
The primary challenge in transmission is **energy loss due to heat**. According to the principle of Joule heating, when current flows through a wire, energy is lost as heat proportional to the square of the current (I²R). To minimize this loss, we use **very high voltage cables** Certificate Physical and Human Geography, GC Leong, p.273. By increasing the voltage, we can transmit the same amount of power with a much lower current, drastically reducing the heat wasted in the wires. This is achieved using **transformers**, which can "step up" voltage for transmission and "step down" voltage for safe home use.
Crucially, transformers rely on **electromagnetic induction**, which requires a time-varying magnetic flux. This is why our grid uses **Alternating Current (AC)**. Because a steady **Direct Current (DC)** produces a constant magnetic field, it cannot be transformed (stepped up or down) in a steady state. This limitation makes AC the standard for grid transmission. Once the power reaches your home, safety is managed by devices like the **electric fuse**, which protects appliances from **overloading** or **short-circuiting** by melting and breaking the circuit if the current becomes dangerously high Science, NCERT Class X, p.205.

Power Source	Average Generation Tariff (Approx.)
Solar / Wind	Rs. 2.0 - 3.0 per unit
Thermal	Rs. 3.0 - 3.5 per unit
Nuclear	Rs. 3.0 - 4.0 per unit
Hydro	Rs. 5.0 - 6.0 per unit

Source: Indian Economy, Vivek Singh, p.431

Sources: Indian Economy, Nitin Singhania, Infrastructure, p.448; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.273; Science, NCERT Class X, Magnetic Effects of Electric Current, p.205; Indian Economy, Vivek Singh, Infrastructure and Investment Models, p.431

5. Household Electrical Circuits and Safety (intermediate)

In our homes, electricity is delivered through a system designed for both efficiency and safety. The standard domestic power supply in India consists of three main wires: the Live wire (usually red insulation), the Neutral wire (black), and the Earth wire (green). The potential difference between the live and neutral wires is typically 220 V. Unlike a simple battery circuit, household appliances are connected in a parallel circuit. This is crucial because a parallel arrangement ensures that every appliance receives the same voltage (220 V) and can be operated independently with its own switch Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.205. If appliances were connected in series, the failure of a single bulb would break the entire circuit, and different gadgets—like a high-power heater and a low-power LED—would not receive the specific current levels they need to function correctly Science, Class X (NCERT 2025 ed.), Electricity, p.187.

Safety is managed through two primary mechanisms: Earthing and the Electric Fuse. The Earth wire is connected to a metal plate deep in the earth near the house; it serves as a low-resistance path for leakage current. If the insulation of an appliance like a refrigerator fails, the current flows into the earth rather than through the user, preventing severe shocks Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206. Meanwhile, the fuse is a safety device placed in series with the circuit. It consists of a wire with a specific low melting point. If the current exceeds a safe limit due to overloading (connecting too many appliances) or a short circuit (live and neutral wires touching), the fuse wire melts and breaks the circuit before the heat can cause a fire Science, Class X (NCERT 2025 ed.), Electricity, p.190.

Feature	Series Connection	Parallel Connection (Domestic)
Voltage	Divided across components	Constant (220 V) for all components
Reliability	One failure stops everything	Independent operation of each device
Current	Same through all devices	Divided based on appliance need

It is also important to understand how power reaches our homes. Transformers are used to adjust these voltage levels for efficient transmission. However, transformers rely on electromagnetic induction, which requires a constantly changing magnetic flux. This means they only work with Alternating Current (AC). If you were to apply a steady Direct Current (DC) to a transformer, the magnetic field would remain static, no induction would occur in the secondary coil, and the primary coil might even overheat and burn out due to low resistance.

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.205; Science, Class X (NCERT 2025 ed.), Electricity, p.187; Science, Class X (NCERT 2025 ed.), Electricity, p.190; Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.206

6. Transformer: Principle and Limitations (exam-level)

A transformer is a passive electrical device that transfers electrical energy from one circuit to another through the process of electromagnetic induction. At its core, it consists of two coils of wire—the primary and the secondary—wound around a common iron core. The fundamental principle is Mutual Induction: when an alternating current (AC) flows through the primary coil, it creates a continuously changing magnetic flux in the core. This changing flux then passes through the secondary coil, inducing a voltage across its terminals. According to Faraday’s Law, the induced voltage is directly proportional to the rate of change of magnetic flux.

The primary function of a transformer is to change voltage levels. This is achieved by varying the turns ratio (the ratio of the number of turns in the primary coil to the secondary coil). If the secondary coil has more turns than the primary, it is a step-up transformer (increasing voltage); if it has fewer, it is a step-down transformer. It is vital to remember that while voltage changes, the total power (P = VI) remains theoretically constant (minus minor losses). Therefore, if a transformer steps up the voltage, the current must decrease proportionally to satisfy the conservation of energy, a concept rooted in the relationship between power, current, and resistance seen in Science, Class X (NCERT 2025 ed.), Electricity, p.193.

One of the most critical limitations of a transformer is that it cannot operate on steady Direct Current (DC). In a steady DC circuit, the current is constant, meaning the magnetic flux produced is also constant. Since there is no change in flux over time, no electromotive force (EMF) is induced in the secondary coil. Using steady DC would only result in the primary coil acting as a simple resistor, potentially overheating due to high current (I²R losses) without transferring any energy to the secondary side. This is why our national power grid relies on Alternating Current—it allows us to efficiently step up voltages for long-distance transmission and step them down for safe domestic use.

Sources: Science, Class X (NCERT 2025 ed.), Electricity, p.193

7. Solving the Original PYQ (exam-level)

To solve this question, you must synthesize your knowledge of Faraday’s Law of Electromagnetic Induction and the fundamental differences between Alternating Current (AC) and Direct Current (DC). A transformer operates on the principle of mutual induction, where a change in current in the primary coil creates a time-varying magnetic flux that induces a voltage in the secondary coil. Since Assertion (A) highlights the core function of a transformer—altering voltage levels through specific winding ratios—it aligns perfectly with these physical principles. However, for this induction to occur continuously, the magnetic flux must be constantly changing, which is a characteristic inherent to AC but absent in steady-state DC.

Walking through the logic, Reason (R) serves as the critical pivot point for your decision. In a DC circuit, the current flows at a steady rate, resulting in a constant magnetic field rather than a changing flux. Without a change in flux over time, no electromotive force (EMF) is induced in the secondary winding, effectively making the transformer useless. Therefore, while the assertion correctly describes the device's utility, the reason provided is a scientific impossibility. This direct contradiction leads us to the correct answer: (C) A is true but R is false.

In the UPSC context, options (A) and (B) are classic distractors designed to catch candidates who recognize the term "transformer" but overlook its underlying physics. A common trap is the assumption that any electrical component is universally applicable to all circuits. By testing the operational constraints of the device—specifically that it requires a fluctuating input—the exam rewards students who understand that induction requires variation. As noted in ScienceDirect, transformers are specifically designed for AC because steady DC produces no continuous changing flux, making Reason (R) fundamentally incorrect.