General Science I — Physics and Chemistry Fundamentals

Why This Chapter Matters

General science sections in competitive exams like the VRO/VRA test are not meant to make you a physicist or a chemist. They test whether you retained the core scientific literacy expected of anyone who completed a general school-level education — literacy that also happens to be genuinely useful in everyday administrative and rural life. Understanding basic physics helps you make sense of everything from how water is pumped for irrigation to why electrical safety matters when your office or a government building has faulty wiring. Understanding basic chemistry helps you make sense of fertilisers, water purity, and common safety hazards. This chapter revisits the essential physics and chemistry concepts that recur most often in general science sections of Indian competitive exams, explained in a way designed to stick, with an emphasis on the reasoning behind each fact rather than rote lists, since reasoning is what lets you answer a question phrased in an unfamiliar way.

Part A: Physics Fundamentals

Units and Measurement

Physics begins with measurement, and the internationally standardised system used for this is the International System of Units, commonly called SI units. The seven base SI units are: metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). Every other physical quantity — speed, force, energy, pressure, and so on — is derived from combinations of these base units. For instance, speed is distance divided by time, so its unit is metres per second (m/s); force, by Newton's second law, is mass times acceleration, so its unit, the newton (N), is equivalent to kilogram-metre per second squared (kg·m/s²).

Motion: Speed, Velocity, and Acceleration

Speed is the rate at which an object covers distance, without regard to direction — a purely numerical (scalar) quantity. Velocity is speed in a specified direction — a directional (vector) quantity. This distinction is commonly tested: two cars can have the same speed but different velocities if they are travelling in different directions, and an object moving in a circle at constant speed still has continuously changing velocity because its direction keeps changing. Acceleration is the rate of change of velocity over time — an object accelerates whenever its speed changes, its direction changes, or both.

Newton's Laws of Motion

Sir Isaac Newton's three laws of motion form the foundation of classical mechanics, and are worth knowing precisely because they are tested frequently and because confusing them is a common error.

• First Law (Law of Inertia): An object at rest stays at rest, and an object in motion continues in motion at constant velocity, unless acted upon by an external unbalanced force. This explains everyday experiences like why passengers lurch forward when a moving vehicle suddenly brakes — their bodies, due to inertia, tend to continue moving forward even as the vehicle stops.
• Second Law: The force acting on an object equals its mass multiplied by its acceleration (F = ma). This tells us that, for a given force, a heavier object accelerates less than a lighter one, and that a larger force produces greater acceleration for the same mass.
• Third Law: For every action, there is an equal and opposite reaction. When you push against a wall, the wall pushes back against you with equal force in the opposite direction — this is why you can feel the resistance, and it is also the basic principle behind how a rocket propels itself forward by expelling exhaust gases backward.

Gravity and Weight

Gravity is the force of attraction between any two masses; on Earth's surface, gravity gives objects weight by pulling them toward the planet's centre. It is important to distinguish mass from weight, a distinction frequently tested: mass is the amount of matter in an object, measured in kilograms, and does not change regardless of location; weight is the force exerted on that mass by gravity, measured in newtons, and does change depending on the local gravitational pull — an object weighs less on the Moon than on Earth because the Moon's gravity is weaker, even though its mass is unchanged.

Work, Energy, and Power

Work, in the physics sense, is done when a force causes displacement of an object in the direction of the force; if you push against an immovable wall, you may feel tired, but in the strict physics sense you have done no work, because there was no displacement. Energy is the capacity to do work, and it exists in many forms — kinetic energy (energy of motion), potential energy (stored energy due to position, such as a raised weight or a stretched spring), thermal energy, chemical energy, electrical energy, and so on. The Law of Conservation of Energy states that energy cannot be created or destroyed, only converted from one form to another — a foundational principle worth remembering because many physics questions are essentially testing whether you understand that energy conversion, not creation or loss, is what is happening in a given scenario. Power is the rate at which work is done or energy is transferred, measured in watts.

Heat and Temperature

Temperature measures how hot or cold something is — technically, the average kinetic energy of the particles in a substance. Heat is the energy transferred between objects due to a temperature difference, flowing naturally from a hotter object to a colder one until thermal equilibrium is reached. Common temperature scales include Celsius (used widely, with 0°C as water's freezing point and 100°C as its boiling point at standard atmospheric pressure) and Kelvin (the SI unit of temperature, where 0 K, called absolute zero, is the theoretical point at which particle motion is at its minimum; 0°C equals 273.15 K).

Light: Reflection and Refraction

Reflection is the bouncing back of light when it strikes a surface — the basis of how mirrors work, governed by the law that the angle of incidence equals the angle of reflection. Refraction is the bending of light as it passes from one transparent medium into another with a different density (for example, from air into water), caused by the change in the speed of light between the two media — this is why a straight stick appears bent at the point it enters water. Convex lenses (thicker in the middle) converge light rays and are used to correct long-sightedness and in magnifying glasses; concave lenses (thinner in the middle) diverge light rays and are used to correct short-sightedness.

Sound

Sound is a form of energy that travels as a mechanical wave, requiring a medium (solid, liquid, or gas) to propagate — unlike light, sound cannot travel through a vacuum, because it depends on the vibration of particles in a medium being passed along. Sound generally travels fastest through solids, slower through liquids, and slowest through gases, because particles in solids are most tightly packed and can transmit vibrations most efficiently. The frequency of a sound wave determines its pitch (how high or low it sounds), while amplitude determines its loudness.

Electricity Basics

Electric current is the flow of electric charge, conventionally measured in amperes. Voltage (or potential difference) is the "push" that drives current through a circuit, measured in volts. Resistance is the opposition a material offers to the flow of current, measured in ohms. Ohm's Law relates these three quantities: voltage equals current multiplied by resistance (V = IR) — a foundational relationship worth memorising precisely, since it is one of the most commonly tested equations in basic physics sections. A circuit can be a series circuit, where components are connected end to end so the same current flows through each in sequence (if one component fails, the whole circuit typically breaks), or a parallel circuit, where components are connected across common points so each branch can operate independently (a failure in one branch does not necessarily stop current in the others) — this is part of why household electrical wiring uses parallel circuits, so that one appliance failing or being switched off does not cut power to every other appliance in the house.

Magnetism and Electromagnetism

Magnets attract certain materials (notably iron, nickel, and cobalt) and exhibit two poles (north and south) such that like poles repel and unlike poles attract. Electromagnetism describes the deep connection between electricity and magnetism: a moving electric current creates a magnetic field around it, and conversely, a changing magnetic field can induce an electric current in a nearby conductor — this second principle, electromagnetic induction, is the basic working principle behind electric generators, which convert mechanical energy into electrical energy.

Part B: Chemistry Fundamentals

Matter and Its States

Matter is anything that has mass and occupies space, and it commonly exists in three familiar states: solid (fixed shape and volume, particles tightly packed), liquid (fixed volume but takes the shape of its container, particles close but able to move past one another), and gas (no fixed shape or volume, particles widely spaced and moving freely). A fourth state, plasma, exists at very high energy levels (as in stars or lightning) where electrons are stripped from atoms, though this is less commonly tested at this exam level. Changes between states — melting (solid to liquid), freezing (liquid to solid), evaporation/boiling (liquid to gas), condensation (gas to liquid), and sublimation (solid directly to gas, without passing through a liquid state, as seen with substances like camphor or dry ice) — are physical changes, meaning the substance's chemical identity does not change even though its physical form does.

Atoms, Elements, and the Periodic Table

An atom is the smallest unit of an element that retains the chemical properties of that element, composed of a nucleus (containing positively charged protons and neutral neutrons) surrounded by negatively charged electrons in motion around it. An element is a pure substance made up of only one type of atom (for example, oxygen, iron, or gold), and cannot be broken down into simpler substances by ordinary chemical means. The periodic table organises all known elements by increasing atomic number (the number of protons in the nucleus) into rows called periods and columns called groups, arranged so that elements with similar chemical properties fall into the same group — for instance, the noble gases (like helium, neon, and argon) form a group known for being largely chemically unreactive because their outer electron shells are already complete.

Compounds and Mixtures

A compound is a pure substance formed when two or more different elements chemically combine in a fixed ratio, producing a new substance with properties distinct from its constituent elements — for example, water (H₂O) is a compound formed from hydrogen and oxygen, and its properties (a liquid at room temperature, capable of extinguishing fire) are entirely different from those of hydrogen gas or oxygen gas individually. A mixture, by contrast, is formed when two or more substances are combined without a fixed chemical ratio and without a new substance being chemically formed — the original substances retain their individual properties and can generally be separated back out by physical means (such as filtration, evaporation, or distillation). This distinction — compounds involve chemical combination in fixed proportions forming something new, while mixtures involve physical combination without forming something chemically new — is one of the most fundamental and frequently tested ideas in basic chemistry.

Acids, Bases, and the pH Scale

Acids are substances that release hydrogen ions in water and typically taste sour, turn blue litmus paper red, and react with metals and carbonates; common examples include vinegar (acetic acid) and the acid found in citrus fruits (citric acid). Bases are substances that release hydroxide ions in water (or otherwise accept hydrogen ions) and typically feel soapy, turn red litmus paper blue; common examples include soap and household ammonia solutions. The pH scale measures how acidic or basic (alkaline) a solution is, running from 0 to 14: a pH of 7 is neutral (pure water), values below 7 indicate increasing acidity as the number decreases, and values above 7 indicate increasing alkalinity as the number increases. Neutralisation is the chemical reaction between an acid and a base that produces a salt and water, and results in a solution closer to neutral pH — this principle is applied practically, for instance, in treating acidic soil with lime (which is basic) to bring soil pH closer to neutral for better crop growth, a fact with obvious relevance to agricultural extension work that revenue and village-level officials sometimes get asked about informally.

Chemical Reactions and Equations

A chemical reaction is a process in which one or more substances (reactants) are transformed into different substances (products) through the breaking and forming of chemical bonds. Common types include combination reactions (two or more substances combine to form one product), decomposition reactions (one substance breaks down into two or more simpler substances, often requiring heat, light, or electricity), displacement reactions (a more reactive element displaces a less reactive one from a compound), and combustion reactions (a substance reacts rapidly with oxygen, releasing heat and light, as in burning). The Law of Conservation of Mass, a foundational chemistry principle, states that matter is neither created nor destroyed in a chemical reaction — the total mass of reactants equals the total mass of products, which is why chemical equations must always be balanced (the same number of atoms of each element must appear on both sides of the equation).

Metals and Non-Metals

Metals generally share characteristic properties: they are lustrous (shiny), malleable (can be hammered into sheets), ductile (can be drawn into wires), good conductors of heat and electricity, and typically solid at room temperature (with mercury as a notable exception, being liquid at room temperature). Non-metals generally lack these properties: they are typically dull in appearance, brittle if solid, poor conductors of heat and electricity (with the notable exception of graphite, a form of carbon that conducts electricity despite being a non-metal — a frequently tested exception). Common metals include iron, aluminium, copper, and gold; common non-metals include oxygen, nitrogen, carbon, and sulphur.

Water Chemistry — Practical Relevance

Water is a compound of hydrogen and oxygen (H₂O) and is often called the universal solvent because it dissolves a very wide range of substances, which is precisely why natural water sources readily pick up dissolved minerals and, unfortunately, pollutants. Hard water contains a relatively high concentration of dissolved calcium and magnesium salts, which reduces soap's ability to lather effectively and can cause scale (mineral deposit) build-up in pipes and heating equipment over time; soft water lacks these minerals in significant quantity. This is practically relevant knowledge for understanding common rural water-supply issues and basic water quality discussions that come up in village administration.

Common Exam Traps and Points of Confusion

• Mass vs weight: Mass is constant and measured in kilograms; weight depends on gravity and is measured in newtons. Do not treat them as interchangeable in a physics context, even though everyday language often does.
• Speed vs velocity: Speed is scalar (magnitude only); velocity is vector (magnitude and direction). An object can have constant speed with changing velocity if its direction is changing.
• Heat vs temperature: Temperature is a measure of average particle kinetic energy (a property of a body); heat is energy in transit between bodies due to a temperature difference. A small object and a large object can be at the same temperature while containing very different amounts of heat energy.
• Compound vs mixture: A compound is a chemical combination in a fixed ratio, forming a new substance; a mixture is a physical combination, not chemically new, and separable by physical means.
• Physical change vs chemical change: A physical change (like melting ice or dissolving salt in water) does not alter the chemical identity of the substance and is generally reversible; a chemical change (like burning wood or rusting iron) produces a new substance with different properties and is generally not easily reversible.
• Series vs parallel circuits: In series, the same current flows through all components and a break anywhere stops the whole circuit; in parallel, voltage is common across branches and a break in one branch does not necessarily stop current in others.

How to Retain This for the Exam

The most effective way to hold onto physics and chemistry fundamentals for a general studies exam is not to memorise isolated facts, but to anchor each concept to a concrete everyday example, exactly as this chapter has tried to do throughout — Newton's third law to a rocket or a wall push, refraction to a bent-looking stick in water, hard water to soap not lathering well, and so on. When a question is phrased in an unfamiliar way, it is this underlying reasoning, not a memorised sentence, that will let you work out the correct answer. Revisit this chapter close to your exam date specifically to refresh the distinctions flagged in the "common exam traps" sections above, since these paired concepts (mass/weight, speed/velocity, compound/mixture, and so on) are exactly where competitive exams most often set their trickiest questions.