Master Everyday Science for the RPSC exam

A hypothesis is an initial, testable proposal that offers a potential explanation for an observation. Unlike a law or theory, it is not yet proven but provides a framework for collecting data to support or refute the claim.

The control group remains unexposed to the experimental variable, letting investigators measure the exact influence of the independent variable and ensuring observed changes are not due to external factors or chance.

Inductive reasoning synthesizes specific instances into a broad generalization, observing patterns in data to derive probable conclusions about larger populations or universal principles.

Scientific laws concisely describe what happens (often mathematically), while theories offer comprehensive, evidence-based explanations of how or why phenomena occur.

Methodology starts with observation, then a testable hypothesis, and must be reproducible. If data contradicts the hypothesis, researchers refine or replace the hypothesis rather than discard the data.

Peer review is a quality-control mechanism where independent experts evaluate methodology, data interpretation, and originality so only technically accurate, logically consistent studies are published.

Control variables are external factors kept unchanged to ensure a fair test, letting researchers attribute changes in the dependent variable solely to the independent variable.

Communicating findings (publishing or presenting) is the concluding stage, letting others evaluate, replicate, and build upon the work.

Models are simplified representations that highlight essential features while ignoring irrelevant details. Because they are approximations, they are not exact replicas of reality.

The independent variable is the factor a researcher changes to observe its effects; it acts as the hypothesized cause within an experiment.

When the bus stops, friction brings the lower body to rest with the bus, but the upper body continues moving forward due to inertia, so the person falls forward. R correctly explains A.

Newton's second law states net force is directly proportional to mass and the resulting acceleration, expressed as F = ma.

For every action there is an equal and opposite reaction. The forward force on the bullet produces an equal backward force on the gun, causing recoil.

Momentum is a vector quantity calculated by multiplying mass by velocity; greater mass or speed gives greater momentum.

Earth's gravity acts as the centripetal force, constantly pulling the satellite inward and balancing its tangential velocity for a stable circular path.

Inertia of rest → dust from a beaten carpet; inertia of motion → athlete unable to stop at the finish line; third law → swimming (action–reaction); conservation of momentum → rocket propulsion.

Rolling friction is significantly LOWER than sliding friction (which is why wheels move heavy loads efficiently), so the statement is incorrect.

By the impulse-momentum theorem, impulse (force × time) equals the change in momentum, so both share the same dimensions and units (N·s).

Newton's first law is the law of inertia: an object stays at rest or in uniform motion unless acted upon by an external force.

An inertial frame is at rest or moving at constant velocity. Newton's first law holds in such frames; non-inertial (accelerating/rotating) frames introduce fictitious forces.

Gravitational force is directly proportional to the product of masses and inversely proportional to the square of the distance between their centers (inverse-square law).

Mass is scalar and constant; weight is a vector gravitational force. A physical object can never have zero mass, so statement IV is incorrect.

Earth is an oblate spheroid; the distance from centre to surface is shortest at the poles, so gravitational pull (and g) is maximum at the poles and minimum at the equator.

In free fall (ignoring air resistance), all objects experience constant acceleration due to gravity (≈9.8 m/s²); velocity increases uniformly but the rate stays the same.

Escape velocity for Earth is about 11.2 km/s; at this speed kinetic energy exactly balances gravitational potential energy.

Henry Cavendish measured G using a torsion balance in his 1798 experiment. Newton formulated the law but did not determine the constant's value.

Astronauts and their spacecraft are in continuous free fall toward Earth; the surface curves away at the same rate they fall, so no normal force acts between them.

Surface gravity depends on mass and radius. Mars (weakest) < Earth < Jupiter (strongest), giving the order Mars, Earth, Jupiter.

The law of equal areas results from conservation of angular momentum in a central force field; a planet speeds up nearer the Sun to keep angular momentum constant.

In a vacuum, air resistance is absent, so all objects fall at the same rate regardless of mass or shape. There is no exception.

Work = F × d × cosθ. When force is perpendicular to displacement, cos 90° = 0, so no work is done (e.g., carrying a load horizontally at constant speed).

KE = ½ mv². Because velocity is squared, doubling it makes KE four times the original (assuming mass is constant).

The kilowatt-hour (kWh) is the unit utilities use to bill electrical energy. One kWh equals 3.6 million joules; the joule is too small for commercial billing.

A microphone converts sound energy into electrical signals (not electrical into sound). A loudspeaker does the reverse, so statement IV is incorrect.

At the mean position KE is maximum; as the pendulum rises to the extreme, speed decreases and height increases, converting kinetic energy into potential energy.

One mechanical horsepower is defined as approximately 746 watts, still used for rating engines and large motors.

Work = mgh = 10 × 9.8 × 5 = 490 J, equal to the gravitational potential energy gained.

Energy cannot be created or destroyed in an isolated system; it only changes form, so total energy remains constant.

Loudspeaker: electrical→sound; dynamo: mechanical→electrical; photosynthesis: light→chemical; steam engine: heat→mechanical.

Kinetic friction acts opposite to displacement, so the force and displacement are oppositely directed and the work done is negative (energy dissipated as heat).

Conduction is the main mode in solids. In metals, free electrons transport heat rapidly across the lattice, making them excellent conductors.

Radiation transfers energy via electromagnetic waves and needs no medium, which is why the Sun's heat reaches Earth across the vacuum of space.

Absolute zero (0 K) is the lowest theoretical temperature where molecular motion ceases; it equals −273.15 °C.

Between 0 and 4 °C water's density increases (volume decreases) as it warms — anomalous behaviour that keeps the densest water at the bottom and prevents lakes from freezing solid.

Water's high specific heat lets it absorb large amounts of heat with a small temperature rise, making it an ideal coolant. R correctly explains A.

Latent heat of fusion is the energy needed to melt 1 kg of solid to liquid at the melting point without changing temperature, used to break molecular bonds in the lattice.

Differential heating of land and water sets up atmospheric convection currents; warm air rises and cooler air moves in, reversing between day and night.

Mercury expands uniformly over a wide temperature range, giving accurate readings; it is also a good conductor, is visible, and does not wet the glass.

By Kirchhoff's law, good absorbers are good emitters. Dark, rough, matte surfaces absorb and emit thermal radiation most efficiently.

Adding a non-volatile solute causes boiling point elevation; the solute hinders vaporisation, requiring more heat to boil than pure water.

Light is fastest in vacuum and bends (refracts) at boundaries of differing optical density. The law of reflection states the angle of incidence EQUALS the angle of reflection, so III is wrong.

Dispersion separates white light into its constituent colours because different wavelengths refract at slightly different angles — the same effect that forms rainbows.

On hot days, air near the ground is warmer and less dense; light bends and undergoes total internal reflection, producing a shimmering, water-like image.

In myopia images focus in front of the retina. A concave (diverging) lens spreads incoming rays so the image focuses correctly on the retina.

Rayleigh scattering scatters shorter (blue) wavelengths more than longer ones; our eyes are most sensitive to blue, so the sky appears blue.

A concave mirror gives a magnified, upright virtual image when the object is close, letting dentists see fine detail and small cavities.

Total internal reflection → optical fibers; scattering → red sun at sunrise; dispersion → rainbow; refraction → twinkling of stars.

Lens power is the reciprocal of focal length (in metres) and is measured in diopters; a shorter focal length means higher power.

Going from denser to rarer medium, light speeds up and bends away from the normal; beyond the critical angle it undergoes total internal reflection.

The speed of light in vacuum is exactly 299,792,458 m/s, a fixed constant used to define the metre in SI units.

Sound in air is a longitudinal mechanical wave: particles vibrate parallel to the wave's travel, creating compressions and rarefactions, and it needs a medium.

Pitch (how high or low a sound is) is determined by frequency; higher frequency means higher pitch. Amplitude governs loudness instead.

Sound is fastest in solids, speeds up with temperature, and travels faster in humid (less dense) air. It cannot travel through a vacuum, so III is incorrect.

A 0.1 s gap is needed; at ~344 m/s sound travels 34.4 m there and back, so the reflecting surface must be at least 17.2 m away.

SONAR (Sound Navigation and Ranging) sends ultrasonic pulses underwater and times the returning echoes to locate objects.

Humans typically hear 20 Hz to 20,000 Hz. Below is infrasonic, above is ultrasonic; the upper limit drops with age.

Loudness depends on amplitude — the maximum displacement of particles. Larger amplitude carries more energy and is perceived as louder.

Ultrasonography uses ultrasonic waves (above 20,000 Hz) that reflect off internal organs to create real-time images safely and non-invasively.

Sound is slowest in gases (air), faster in liquids (water), and fastest in rigid solids (steel) due to stronger bonds and higher elasticity.

The Doppler Effect: an approaching source compresses waves (higher pitch), a receding source stretches them (lower pitch).

Ohm's law: at constant temperature current is directly proportional to the potential difference (voltage) across the conductor's ends.

In series, resistances add: 2 + 3 + 5 = 10 ohms. The same current flows through each resistor.

An ammeter measures current in amperes and is connected in the circuit path so the full current passes through it.

An ammeter is connected in series so the full current passes through it; it has very low resistance to minimise its effect on the circuit.

Resistance depends on length, area, and material, and increases on stretching. For most metals it RISES with temperature, so statement IV is incorrect.

India's domestic AC supply is at 50 Hz, with a standard voltage of about 220 V.

A fuse uses the heating effect of current: excessive current melts its low-melting-point wire, breaking the circuit and preventing damage.

Joule's law: H ∝ I²Rt. Heat is proportional to the square of the current, the resistance, and the time.

Superconductors show zero resistance below a critical temperature, carrying current without energy loss and expelling magnetic fields (Meissner effect).

Silver conducts best but is too costly and theft-prone for large-scale transmission; copper and aluminium offer a better balance. R correctly explains A.

Outside a magnet, field lines emerge from the north pole and curve into the south pole; inside, they run south to north, forming closed loops.

Maxwell's Right-Hand Thumb Rule: point the thumb along the conventional current and the curled fingers show the circular magnetic field direction.

Soft iron is easily magnetised and demagnetised, so it becomes a strong magnet when current flows and loses magnetism when switched off — ideal for control.

Electromagnetic induction generates an EMF and current by changing the magnetic environment; discovered by Faraday, it underlies generators and transformers.

A motor relies on the force a current-carrying conductor experiences in a magnetic field, producing torque that spins the rotor and converts electrical to mechanical energy.

Left-Hand Rule → force in motors; Right-Hand Rule → induced current in generators; Lenz's Law → conservation of energy; Faraday's Law → magnitude of induced EMF.

Michael Faraday discovered electromagnetic induction in 1831, showing a changing magnetic field induces a current — the basis of motors, generators and transformers.

Iron, nickel and cobalt are ferromagnetic; their atomic magnetic moments align within domains, allowing strong magnetisation and sometimes permanent magnetism.

A commutator is a rotary switch that periodically reverses current direction, keeping the rotor turning continuously in one direction.

Earth's magnetic north pole behaves like the south pole of a bar magnet, which is why a compass's north-seeking end is attracted toward the north.

The nucleus contains protons (positive) and neutrons (neutral), collectively nucleons, which hold nearly all the atom's mass; electrons orbit outside.

Electrons are negatively charged and about 1/1836 the mass of a proton, but they occupy energy levels OUTSIDE the nucleus, so III is incorrect.

Atomic number equals the number of protons in the nucleus and defines the element's identity; in a neutral atom it also equals the electron count.

Isotopes have the same number of protons (same atomic number) but different neutron counts, giving different mass numbers and similar chemical properties.

Isobars have the same mass number but different atomic numbers, so they are different elements with distinct chemical and physical properties.

Niels Bohr proposed the planetary model in 1913, with electrons in fixed energy orbits that jump levels by absorbing or emitting energy.

Some alpha particles deflected at large angles, revealing a tiny, dense, positively charged centre — the atomic nucleus — with the atom mostly empty space.

Order: Dalton (solid sphere) → Thomson (plum pudding) → Rutherford (nuclear) → Bohr (quantised orbits).

Valency, determined by the number of valence (outer-shell) electrons, measures an element's combining capacity as atoms seek a stable noble-gas configuration.

Moseley's modern periodic table arranges elements by increasing atomic number, placing those with similar electronic configurations in the same groups.

An ionic bond forms by complete transfer of electrons (usually metal to non-metal), creating a cation and an anion held by electrostatic attraction.

Water has covalent bonds where oxygen shares electrons with two hydrogen atoms. NaCl, MgO and CaF₂ are ionic compounds.

In metallic bonding, positive ions sit in a lattice surrounded by mobile, delocalised valence electrons, giving metals their conductivity, malleability and lustre.

Ionic compounds have high melting points and conduct when molten or dissolved (not as solids), and dissolve in polar solvents — so only I and III are correct.

Covalent molecules have strong internal bonds but weak intermolecular forces, so little energy is needed to separate molecules — giving low melting/boiling points.

Polar water molecules form hydrogen bonds, much stronger than ordinary van der Waals forces, so significant energy is needed to boil water.

In a coordinate (dative) bond, one atom supplies both shared electrons; once formed it is indistinguishable from a normal covalent bond.

Electronegativity is an atom's tendency to attract a shared electron pair; unequal attraction produces polar bonds and influences molecular polarity.

In N₂, two identical nitrogen atoms share electrons equally (same electronegativity), giving a nonpolar covalent bond. HCl, H₂O and NH₃ are polar.

KCl: ionic; methane: covalent; copper: metallic; ammonium ion: contains a coordinate bond where nitrogen donates an electron pair.

pH measures the concentration of hydrogen ions (H⁺). High H⁺ means low pH (acidic); low H⁺ means high pH (basic).

Blue litmus turning red indicates an acid, which has pH below 7. A pH of 3 clearly represents an acidic solution.

A strong acid ionises completely in water, releasing nearly all its hydrogen ions; weak acids only partially dissociate. Examples: HCl, H₂SO₄.

In neutralisation, H⁺ from the acid combines with OH⁻ from the base to form water, leaving a salt; the solution moves toward neutral pH.

Milk of magnesia is magnesium hydroxide, a mild base that neutralises excess stomach acid to relieve indigestion and heartburn.

Table salt is sodium chloride, not potassium chloride, so pair V is incorrect; the other pairs are correctly matched.

Lactic acid forms when bacteria like Lactobacillus ferment lactose in milk, increasing acidity, coagulating proteins, and giving curd its tangy flavour.

Ants and bees inject formic (methanoic) acid, causing sharp pain and swelling; a mild base like baking soda can neutralise the irritation.

Normal rain is slightly acidic (pH ~5.6) from dissolved CO₂. Below 5.6 it is acid rain, caused by sulfur and nitrogen oxides forming stronger acids.

A strong acid with a weak base gives an acidic salt; on dissolving it hydrolyses to release excess H⁺, giving a solution with pH below 7.

Catenation is carbon's ability to bond with itself into long chains, branches and rings, due to its small size and strong C–C bonds, enabling vast organic diversity.

Graphite has one delocalised electron per atom that conducts electricity, while diamond uses all four valence electrons in bonds, making it an insulator. R explains A.

Buckminsterfullerene (the “buckyball”) has 60 carbon atoms arranged in a hollow sphere of pentagons and hexagons, like a soccer ball.

Unsaturated hydrocarbons have at least one C=C double bond (alkenes) or C≡C triple bond (alkynes), making them more reactive than saturated alkanes.

A homologous series shares a functional group and similar properties, with each member differing by a –CH₂ unit, giving a gradual change in physical properties.

Isomers share a molecular formula but differ in structural arrangement, so they can have markedly different physical and chemical properties.

The carboxyl group (–COOH) defines carboxylic acids, such as acetic acid (vinegar) and citric acid, which show acidic properties.

Alcohol → -ol; aldehyde → -al; ketone → -one; carboxylic acid → -oic acid.

Saponification is the alkaline hydrolysis of fats/oils with a strong base, breaking triglycerides into glycerol and fatty-acid salts (soap).

Methane (CH₄) is the main component of biogas and natural gas, produced by anaerobic decomposition; it burns cleanly and releases significant energy.

Malleability lets metals be hammered or rolled into thin sheets as atomic layers slide over each other. Gold is the most malleable metal.

Mercury is the only common metal that is liquid at standard room temperature due to weak interatomic bonding, used in thermometers and switches.

Bromine is the only non-metal liquid at room temperature — a reddish-brown, volatile halogen used in flame retardants and water treatment.

More reactive metals displace less reactive ones, and gold/platinum sit at the bottom. Only metals ABOVE hydrogen liberate it from acids, so III is wrong.

Amphoteric oxides (e.g., aluminium oxide, zinc oxide) react with both acids and bases to form salt and water.

Calcination heats carbonate ores in limited air, decomposing them to release CO₂ and leave the metal oxide, ready for reduction.

Anodizing thickens the natural oxide layer on aluminium, improving corrosion resistance and hardness; the stable oxide adheres strongly to the metal.

Galvanisation coats iron/steel with zinc, which corrodes sacrificially in preference to the underlying iron even if the coating is scratched.

Aluminium is the most abundant metal in the crust (~8% by weight), found mainly in bauxite; it is light and corrosion-resistant.

Decreasing reactivity: potassium > sodium > calcium > magnesium, i.e., II, IV, I, III.

Robert Hooke observed cork under a microscope in 1665 and coined the term “cell” for the tiny compartments (actually dead plant cell walls).

The claim that all cells have a true nucleus and membrane-bound organelles is false because prokaryotes (e.g., bacteria) lack them — so it is not a postulate.

Prokaryotes lack a membrane-bound nucleus; their DNA lies in a nucleoid region not separated from the cytoplasm by a membrane.

Plant cells have a rigid cellulose cell wall for support and protection; animal cells have only a flexible plasma membrane.

Mitochondria carry out aerobic respiration, converting nutrient energy into ATP, the cell's usable energy, earning the nickname “powerhouses.”

Lysosomes digest, ribosomes make proteins, and vacuoles store substances. Chloroplasts do photosynthesis (not lipid synthesis), so III is wrong.

The Golgi apparatus modifies, sorts and packages proteins and lipids from the ER into vesicles for delivery to their destinations.

RER's rough look comes from ribosomes on its surface, which synthesise proteins destined for secretion or the cell membrane.

Chromoplasts contain carotenoid pigments that give flowers and fruits yellow, orange and red colours, attracting pollinators and seed dispersers.

The fluid mosaic model describes the membrane as a flexible phospholipid bilayer with proteins embedded in it that can move laterally within the fluid layer.

Chlorophyll absorbs light energy (mainly blue and red wavelengths), which drives the reactions converting CO₂ and water into glucose while releasing oxygen.

Glycolysis → cytoplasm; Krebs cycle → mitochondrial matrix; light reaction → thylakoids; Calvin cycle → stroma.

Photolysis splits water into hydrogen ions, electrons and oxygen; the oxygen is released as a byproduct while the rest powers ATP and NADPH production.

Stomata, guarded by guard cells, allow CO₂ in and O₂ out for photosynthesis and also enable transpiration (water-vapour loss).

Aerobic respiration strictly needs oxygen and yields far more ATP, producing CO₂ and water; anaerobic respiration occurs without oxygen and gives lactic acid or ethanol.

ATP stores energy in high-energy phosphate bonds that power cellular processes; it is continuously made during respiration and used during cellular work.

Glycolysis, occurring in the cytoplasm without oxygen, is common to both pathways and breaks glucose into two pyruvate molecules with a small ATP gain.

Light, CO₂, temperature and water are the primary limiting factors. Atmospheric nitrogen is not a direct reactant, so V is not a limiting factor.

During intense exercise, oxygen shortage forces anaerobic respiration, producing lactic acid that lowers muscle pH and causes fatigue and cramps.

R.Q. is the ratio of CO₂ evolved to O₂ consumed during respiration, and varies with the fuel (carbohydrate, fat or protein) being metabolised.

Autotrophs make their own food from inorganic substances using light (photosynthesis) or chemical energy; they form the base of most food chains.

Holozoic nutrition involves ingestion, digestion, absorption, assimilation and egestion of complex food — the mode humans use.

Cuscuta lacks chlorophyll and uses haustoria to penetrate a host plant, absorbing ready-made food and water — a parasitic mode of nutrition.

A thick mucus layer secreted by specialised cells coats the stomach lining and shields it from concentrated HCl, preventing ulcers. R correctly explains A.

Bile salts emulsify large fat globules into tiny micelles, increasing the surface area for lipase enzymes to digest fats efficiently.

Villi are finger-like projections that hugely increase the absorptive surface; each contains capillaries and a lacteal to carry off nutrients.

Vitamin C (and the B-complex) is water-soluble and not stored well in the body, so it must be consumed regularly. A, D, E, K are fat-soluble.

Vitamin A is needed for rhodopsin in the retina; its deficiency causes night blindness and, if untreated, can lead to permanent eye damage.

Kwashiorkor results from severe protein deficiency despite adequate calories, causing a bloated abdomen, thin hair and swollen limbs, especially in children.

Vitamin B1 → Beriberi; Vitamin C → Scurvy; Vitamin D → Rickets; Iron → Anaemia.

Bakelite and melamine are thermosetting plastics: they form permanent cross-links during moulding, creating rigid, heat-resistant structures that do not soften on reheating.

Vulcanisation heats rubber with sulfur, forming cross-links that boost strength, durability and elasticity — used for tyres and hoses.

Rayon is a semi-synthetic fibre regenerated from cellulose (wood pulp); its lustrous, silk-like look earns it the name “artificial silk.”

Brass is mainly copper and zinc; varying proportions tune its properties for instruments, hardware and plumbing fixtures.

Bronze is mainly copper with tin; it is harder and more corrosion-resistant than pure copper, historically used for tools, statues and ship propellers.

Wool has the lowest tensile strength, cotton is stronger, and nylon — a synthetic polymer — is the strongest, giving Wool < Cotton < Nylon.

Kevlar is an aramid fibre about five times stronger than steel by weight; it absorbs high-velocity impact energy, ideal for bulletproof vests and body armour.

Fiberglass embeds fine glass fibres in a plastic/polymer resin matrix, combining the glass's tensile strength with the plastic's light, flexible nature.

Silica (quartz sand) is the main raw material for ordinary glass; soda and limestone are added to lower the melting point.

Calcium oxide (lime) is the most abundant compound in Portland cement, typically over 60% by weight, with silica, alumina and iron oxide also present.

Detergents' salts stay soluble with calcium and magnesium ions in hard water, so they lather well and do not form the insoluble scum that soaps produce.

Bleaching powder is made by reacting chlorine with dry slaked lime and disinfects water. In air it slowly releases chlorine (not oxygen), so III is wrong.

Sodium benzoate preserves acidic foods like juices and jams by inhibiting bacteria, yeasts and moulds, extending shelf life.

Saccharin and aspartame are low-calorie artificial sweeteners many times sweeter than sugar, useful for diabetics and calorie-conscious consumers.

MSG, a salt of glutamic acid, is added to enhance the savoury “umami” flavour of packaged and processed foods.

Antiseptics are applied to living tissue (skin, wounds) to kill or inhibit microbes safely; disinfectants are stronger and used on inanimate surfaces.

Mouth bacteria ferment sugars into acids that erode enamel. Slightly basic toothpaste neutralises these acids, protecting the teeth and balancing oral pH.

Urea (N), superphosphate (P) and muriate of potash (K) supply the NPK macronutrients. Sodium chloride is not a fertiliser.

DDT is an organochlorine insecticide once used against malaria mosquitoes and lice, but environmental persistence and harm led to widespread bans.

Drain cleaners use sodium hydroxide (caustic soda/lye), a strong base that decomposes organic clogs like hair and grease.

Mechanical advantage is the output (load) force divided by the input (effort) force; an MA greater than 1 means a heavy load is moved with less effort.

Scissors are a Class 1 lever: the pivot (fulcrum) lies between the effort (handles) and the load (blades cutting the material).

In a Class 2 lever the load sits between fulcrum and effort; the longer effort arm always gives a mechanical advantage greater than one.

Simple machines can multiply force, speed or distance and change force direction, but they cannot multiply work or energy (conservation of energy), so IV is incorrect.

In a Class 3 lever the effort is between fulcrum and load, so the effort arm is shorter and the mechanical advantage is always less than one, but it multiplies speed/distance (e.g., tweezers).

A single fixed pulley does not multiply force (MA ≈ 1); its value is changing the direction of effort, letting you pull down to lift a load up.

Inclined plane → wheelchair ramp; wedge → axe blade; screw → spiral staircase; wheel and axle → doorknob.

A screw is an inclined plane wrapped spirally around a cylinder; its threads convert rotation into linear force, giving a high mechanical advantage.

Real machines lose some input energy to heat and sound through friction, so output work is always less than input work and efficiency stays below 100%.

Fulcrum → fixed pivot; load → resistance to overcome; effort → force applied; velocity ratio → distance moved by effort ÷ distance moved by load.