Transformer is a kind of appliance that can 1. increase power 2. increase voltage 3. decrease voltage 4. measure current and voltage Select the correct answer using the code given below :

1. Basics of Electric Current: AC vs DC (basic)

To understand electricity, we must first distinguish between the two ways charges can flow through a circuit: Direct Current (DC) and Alternating Current (AC). In DC, the electric charge flows in only one constant direction. This is the type of power we get from batteries or solar cells. Because the direction never changes, the magnetic field produced by a DC wire remains steady in its orientation Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.200. While DC is perfect for low-voltage electronics, it is difficult to transmit over long distances without significant energy loss. In contrast, Alternating Current (AC) is characterized by a flow of charge that periodically reverses its direction. In the Indian power grid, this reversal happens so rapidly that the current completes 50 full cycles every second (a frequency of 50 Hz). The primary reason the world relies on AC for national grids is its transmissibility. AC voltage can be easily manipulated—stepped up to very high levels to travel across states with minimal loss, and then stepped down for safe use in our homes. As established in Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.203, the direction of magnetic force depends on the direction of the current; thus, in an AC system, the electromagnetic forces are also dynamic.

Feature	Direct Current (DC)	Alternating Current (AC)
Direction	Unidirectional (Single direction)	Bidirectional (Reverses periodically)
Frequency	Zero	50 Hz (India) / 60 Hz (USA)
Common Sources	Batteries, Fuel cells, Solar panels	Power plants, Wall outlets, Generators
Long Distance Transport	Expensive and difficult due to energy loss	Efficient and easy using Transformers

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.200; Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.203

2. Electromagnetic Induction Principles (intermediate)

At the heart of modern electrical systems lies the principle of Electromagnetic Induction (EMI), a discovery championed by the 19th-century scientist Michael Faraday. Faraday, whose insatiable curiosity led him to study everything from the chemistry of a candle to the mysteries of magnets, found that electricity and magnetism are not separate forces but are deeply intertwined Science-Class VII, Changes Around Us: Physical and Chemical, p.65. Simply put, EMI is the process where a changing magnetic field induces (or creates) an electric current in a conductor. This isn't just a lab trick; it is the reason your phone charges and your lights turn on.

To understand how this works, imagine a coil of wire. If you move a magnet through that coil, the magnetic flux (the total magnetic field passing through the loop) changes. This change "pushes" the electrons in the wire, creating an induced current. We can determine the direction of this induced current using Fleming's Right-Hand Rule Science, class X, Magnetic Effects of Electric Current, p.207. The magnitude of this effect is greatest when the movement is perpendicular to the magnetic field lines Science, class X, Magnetic Effects of Electric Current, p.203. This fundamental principle allows us to convert mechanical energy into electrical energy in generators.

One of the most vital applications of EMI is the Transformer. A transformer is a static electrical device—meaning it has no moving parts—that transfers energy between two or more circuits through mutual induction. It consists of a primary coil and a secondary coil. When alternating current (AC) flows through the primary coil, it creates a constantly changing magnetic field that "links" with the secondary coil, inducing a voltage there. By varying the number of turns in these coils, we can create a step-up transformer (increasing voltage) or a step-down transformer (decreasing voltage).

However, there is a catch rooted in the Law of Conservation of Energy: a transformer cannot create power. Since Power (P) = Voltage (V) × Current (I), any increase in voltage must be balanced by a proportional decrease in current (minus small energy losses). This is why high-voltage power lines have relatively low current—it makes long-distance transmission more efficient. While specialized instrument transformers like Current Transformers (CTs) or Potential Transformers (PTs) are used to scale down values for safe measurement, the core function of the transformer itself remains the fundamental alteration of voltage levels for the grid.

Sources: Science-Class VII, Changes Around Us: Physical and Chemical, p.65; Science, class X, Magnetic Effects of Electric Current, p.203; Science, class X, Magnetic Effects of Electric Current, p.207

3. Electrical Power and Transmission Efficiency (intermediate)

To understand how electricity reaches our homes from a distant power plant, we must first look at the concept of Electrical Power (P). Power is the rate at which electrical energy is consumed or transferred in a circuit. Mathematically, it is expressed as the product of Voltage (V) and Current (I), written as P = VI. Because of Ohm’s Law, we can also express power in terms of resistance (R) as P = I²R or P = V²/R Science, class X (NCERT 2025 ed.), Electricity, p.193. This first-principle understanding is crucial because it reveals a major engineering challenge: the heating effect of current.

When electricity flows through a wire, some energy is inevitably lost as heat due to the wire's resistance. According to Joule’s Law of Heating, this loss is proportional to the square of the current (I²). Therefore, if we try to transmit high current over long distances, most of the energy would dissipate as heat before reaching its destination, potentially damaging infrastructure Science, Class VIII, NCERT (Revised ed 2025), Electricity: Magnetic and Heating Effects, p.54. To solve this, engineers use high-voltage transmission. Since Power = Voltage × Current, we can transmit the same amount of power by increasing the voltage and decreasing the current. By dropping the current significantly, we reduce the I²R losses to a negligible level, allowing electricity to be transported over 1,600 km with ease Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.273.

The bridge between generation and consumption is the transformer. A transformer is a static device that uses electromagnetic induction to change AC voltage levels without changing the frequency. It follows the law of conservation of energy: input power equals output power (ideally).

• Step-up Transformers: Used at power plants to increase voltage (and decrease current) for efficient long-distance travel.
• Step-down Transformers: Used at local substations to decrease voltage to a safe level (e.g., 220V) for household use.

While materials like copper and aluminium are chosen for their low resistance to further aid efficiency Science, class X (NCERT 2025 ed.), Electricity, p.194, the transformer remains the primary tool for managing the trade-off between voltage and current.

Sources: Science, class X (NCERT 2025 ed.), Electricity, p.193; Science, Class VIII, NCERT (Revised ed 2025), Electricity: Magnetic and Heating Effects, p.54; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.273; Science, class X (NCERT 2025 ed.), Electricity, p.194

4. Measuring Instruments: Ammeters and Voltmeters (basic)

To understand how we measure electricity, we must first distinguish between the two fundamental quantities: Electric Current and Potential Difference. Just as you might measure the flow of water through a pipe and the pressure difference between two points in that pipe, we use specific instruments—the Ammeter and the Voltmeter—to quantify these electrical properties.

An Ammeter is an instrument used to measure the electric current (I) in a circuit. For it to measure the flow accurately, it must be connected in series with the component through which you want to measure the current. Think of it like a flow meter in a water pipe; the water must pass through the meter to be counted. Because we want the ammeter to measure the current without actually reducing it, an ideal ammeter has very low resistance. As noted in Science, Class X (NCERT), Electricity, p. 182, the value of the current in an ammeter remains the same regardless of its position in a series circuit, which confirms that current is a measure of the continuous flow through a single path.

Conversely, a Voltmeter measures the potential difference (V) between two points. It doesn't measure flow through itself; instead, it compares the electrical "pressure" at one point versus another. Therefore, it is always connected in parallel across the points where the potential difference is to be measured Science, Class X (NCERT), Electricity, p. 185. To ensure that the voltmeter doesn't "steal" current from the main circuit (which would change the very voltage it is trying to measure), it is designed with very high resistance.

Feature	Ammeter	Voltmeter
Measures	Electric Current (Amperes)	Potential Difference (Volts)
Connection	Series	Parallel
Ideal Resistance	Zero (Very Low)	Infinite (Very High)

Sources: Science, Class X (NCERT), Electricity, p.182; Science, Class X (NCERT), Electricity, p.185

5. Other Power Devices: Rectifiers and Inverters (intermediate)

To understand modern power electronics, we must first distinguish between the two ways electricity flows: Direct Current (DC), where electrons flow steadily in one direction (like from a battery), and Alternating Current (AC), where the flow periodically reverses direction. While our national grid and home wall sockets provide AC at a potential difference of 220V Science, class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.204, many of our modern gadgets and renewable energy sources operate on DC. This creates a need for devices that can switch electricity from one form to another.

A Rectifier is a device that converts AC into DC. It acts like a "one-way valve" for electricity, typically using components called diodes that allow current to pass in only one direction while blocking the return flow. You use a rectifier every time you charge your smartphone; the "charging brick" takes the 220V AC from your wall and rectifies it into the low-voltage DC your battery requires. Conversely, an Inverter performs the opposite task: it converts DC into AC. This is essential in renewable energy systems, such as solar power plants, where the electricity generated as Direct Current must be converted to Alternating Current to be compatible with the power grid Environment, Shankar IAS Academy, Renewable Energy, p.288.

It is important to distinguish these from Transformers. While a transformer changes the voltage level of AC (stepping it up or down), it does not change the nature of the current itself—AC remains AC. Rectifiers and Inverters, however, change the very character of the electrical flow. In a typical home "Inverter" system used for power backups, both devices work together: a rectifier converts grid AC to DC to charge the battery, and an inverter converts that stored DC back into AC when the power goes out.

Device	Conversion Direction	Common Application
Rectifier	AC → DC	Battery chargers, DC power supplies for electronics.
Inverter	DC → AC	Solar panels feeding the grid, UPS (Uninterruptible Power Supply).

Sources: Science, class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.204; Environment, Shankar IAS Academy, Renewable Energy, p.288

6. Types of Transformers: Step-up and Step-down (exam-level)

A transformer is a static electrical device that transfers energy between two or more circuits through electromagnetic induction. At its heart, a transformer consists of a magnetic core (usually soft iron) wrapped with two sets of coils: the primary winding (input) and the secondary winding (output). While these coils are not physically connected, they are linked by a fluctuating magnetic field, much like the field lines seen in a solenoid Science, Class X, Magnetic Effects of Electric Current, p.201. The primary function of a transformer is to alter Alternating Current (AC) voltage levels to suit different needs, from high-voltage long-distance transmission to low-voltage home appliances.

Transformers are classified into two main types based on their voltage output:

• Step-up Transformer: It increases the voltage from the primary to the secondary side. This is achieved by having more turns in the secondary winding than in the primary winding (Nₛ > Nₚ). These are typically used at power stations to prepare electricity for long-distance travel.
• Step-down Transformer: It decreases the voltage. Here, the secondary winding has fewer turns than the primary winding (Nₛ < Nₚ). These are the units you see on utility poles in neighborhoods, reducing high-line voltage to a safe 220V for household use.

A crucial concept for the UPSC aspirant to master is the Law of Conservation of Energy. A transformer does not create power; it only transforms its components. In an ideal transformer, the input power equals the output power (Pᵢₙ = Pₒᵤₜ). Since electrical power is the product of voltage and current (P = VI) Science, Class X, Electricity, p.193, an increase in voltage must result in a proportional decrease in current, and vice versa. This is why we "step up" voltage for transmission—by increasing voltage, we lower the current, which significantly reduces the energy lost as heat (I²R) in the transmission wires Science, Class X, Electricity, p.194.

Feature	Step-up Transformer	Step-down Transformer
Voltage (V)	Increases (Vₛ > Vₚ)	Decreases (Vₛ < Vₚ)
Current (I)	Decreases (Iₛ < Iₚ)	Increases (Iₛ > Iₚ)
Turns Ratio (N)	Nₛ > Nₚ	Nₛ < Nₚ
Primary Use	Power plants (Generation)	Substations/Homes (Distribution)

Sources: Science, Class X, Magnetic Effects of Electric Current, p.201; Science, Class X, Electricity, p.193; Science, Class X, Electricity, p.194

7. Energy Conservation and Power in Transformers (exam-level)

At its heart, a transformer is a static electrical device that transfers electrical energy from one alternating current (AC) circuit to another through the principle of electromagnetic induction. It consists of two coils—the primary and the secondary—wound around a common magnetic core. Its primary job is to change the voltage levels of electricity. However, a common misconception is that by increasing voltage, we are somehow 'gaining' energy. In reality, the transformer must strictly obey the Law of Conservation of Energy.

According to the power formula, P = VI (where P is power, V is voltage, and I is current), as seen in Science, class X (NCERT 2025 ed.), Electricity, p.191. In an ideal transformer (ignoring minor heat losses), the input power in the primary coil must equal the output power in the secondary coil. This creates an inverse relationship: if a transformer 'steps up' the voltage, the current must 'step down' proportionally to keep the total power constant. Conversely, a 'step-down' transformer reduces voltage but increases the available current.

Type of Transformer	Voltage (V)	Current (I)	Turns Ratio (N)
Step-up	Increases (V₂ > V₁)	Decreases (I₂ < I₁)	Secondary has more turns
Step-down	Decreases (V₂ < V₁)	Increases (I₂ > I₁)	Primary has more turns

This trade-off is essential for our national power grid. Electricity is transmitted over long distances at incredibly high voltages to minimize energy loss as heat. By stepping up the voltage, we drastically reduce the current; since heat loss in wires is proportional to the square of the current (I²R), lower current means more energy actually reaches your home instead of being wasted as heat in the transmission lines.

Sources: Science, class X (NCERT 2025 ed.), Electricity, p.191

8. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamental building blocks of electromagnetic induction and the Law of Conservation of Energy, this question serves as the perfect test of how those principles manifest in real-world technology. In your learning path, you discovered that a transformer uses a changing magnetic flux to transfer energy between coils. Its primary utility is to adjust potential difference—a step-up transformer increases voltage for long-distance transmission, while a step-down transformer decreases it for safe residential use. Because these roles are the fundamental definition of the device, statements 2 and 3 are the only correct functional descriptions, leading you to Option (C).

To arrive at this answer, you must effectively navigate two classic traps UPSC uses to test conceptual clarity. Reasoning through the lens of physics, statement 1 is an immediate red flag: since power equals voltage times current (P = VI), an increase in voltage must result in a decrease in current to keep power constant. A transformer cannot create energy; it only transforms it. Similarly, statement 4 is a linguistic trap. While we use instrument transformers (like Potential Transformers) to scale down high voltages so they can be measured, the transformer itself is the voltage regulator, not the measuring instrument (like a voltmeter). By distinguishing between the mechanism of change and the tool of measurement, you can avoid these common distractors and focus purely on the device's core purpose.