General Science Notes: Physics and Chemistry for APPSC, DSC and Police

General science is a scoring section in almost every Andhra Pradesh recruitment paper, whether you are preparing for APPSC Group I to IV, AP DSC, AP Police Constable and SI, or the Grama and Ward Sachivalayam posts. The questions are rarely deep. They test whether you know the standard textbook fact, the correct unit, the right formula, and the common confusion between two similar ideas. Physics and chemistry together usually contribute more than half of the science questions, and almost all of them come from the Class 6 to Class 10 syllabus.

This note is arranged in the order most aspirants find easiest to revise: physics first (motion, work and energy, light, sound, electricity and magnetism, heat), then chemistry (atoms and the periodic table, acids, bases and salts, metals and non-metals, carbon compounds, everyday chemistry). Each section gives the laws, formulae and units, a worked example where one helps, and the traps that cost marks. The facts were checked against the NCERT Class 10 Science textbook (reprint 2026-27) and the NCERT Class 9 Science chapters. Class 9 NCERT was restructured into a new textbook for 2026-27, so a few chapter names differ from older editions; the laws and units below have not changed. Most Andhra Pradesh exams, and the SCERT Andhra Pradesh textbooks used by DSC candidates, still follow the classical sequence of topics, so this note does too.

1. Motion and force

Motion is the change of position with time. Distance is the length of the path travelled and is a scalar (magnitude only). Displacement is the shortest straight-line change of position and is a vector (magnitude and direction). Distance can be larger than displacement but never smaller. In a full circular lap, displacement is zero while distance is the circumference.

Speed is distance divided by time, and its SI unit is metre per second (m/s). Velocity is displacement divided by time. Acceleration is the rate of change of velocity, with the unit m/s squared. Retardation (deceleration) is simply negative acceleration. A body moving in a circle at constant speed is still accelerating, because its direction keeps changing.

The three equations of uniform acceleration are v = u + at, s = ut + half a t squared, and v squared = u squared + 2as, where u is initial velocity, v is final velocity, a is acceleration, t is time and s is displacement. Worked example: a car starts from rest and reaches 20 m/s in 5 seconds. Then a = (20 - 0) / 5 = 4 m/s squared and s = 0 + half times 4 times 25 = 50 m.

Graphs are a favourite. On a distance-time graph, the slope is speed and a straight line means uniform speed. On a velocity-time graph, the slope is acceleration and the area under the graph is the displacement. A horizontal line on a velocity-time graph means uniform velocity, not rest.

Newton's laws form the core of force questions. The first law (law of inertia) says a body stays at rest or in uniform motion unless an external force acts. Inertia depends on mass: more mass, more inertia. The second law says force equals the rate of change of momentum, which for constant mass is F = ma. Momentum is p = mv, with the unit kg m/s. The unit of force is the newton, where 1 N is the force that gives 1 kg an acceleration of 1 m/s squared. The third law says every action has an equal and opposite reaction, but the two forces act on different bodies, so they do not cancel each other. Recoil of a gun and the rocket's upward thrust are standard examples.

Gravitation: the universal law says F = G m1 m2 / r squared. G is the universal gravitational constant, about 6.67 x 10 to the power minus 11 N m squared per kg squared, and it is the same everywhere. The acceleration due to gravity g is about 9.8 m/s squared near the Earth's surface; it is slightly larger at the poles than at the equator, and it decreases with height and with depth. Mass is the quantity of matter, constant everywhere, measured in kg. Weight is the force of gravity on that mass, W = mg, measured in newtons. The Moon's gravity is about one-sixth of Earth's, so a body's weight on the Moon is one-sixth while its mass is unchanged. The escape velocity from Earth is about 11.2 km/s.

Quantity	SI unit	Type
Distance	metre (m)	Scalar
Displacement	metre (m)	Vector
Speed	m/s	Scalar
Velocity	m/s	Vector
Force	newton (N)	Vector
Momentum	kg m/s	Vector

Trap: weight is measured in newtons, not kilograms, in a strict question. Another trap: in free fall without air resistance, a feather and a hammer fall together, because g does not depend on mass.

2. Work, energy and power

Work is done when a force moves its point of application. W = F x s x cos(theta), and when the force and displacement are in the same direction, W = Fs. The SI unit is the joule (J), where 1 J is the work done when 1 N moves a body by 1 m. Work is zero when there is no displacement (pushing a wall) or when the force is perpendicular to displacement (a porter walking on level ground carrying a load on his head).

Energy is the capacity to do work, with the same unit, the joule. Kinetic energy is half m v squared and potential energy near the Earth is mgh. The law of conservation of energy says energy can change form but the total remains constant. A falling object loses potential energy and gains an equal amount of kinetic energy. Doubling the velocity makes kinetic energy four times, a classic numerical trap.

Power is the rate of doing work, P = W / t, with the unit watt (W), equal to 1 J/s. Larger units are the kilowatt (1000 W) and the horsepower (746 W approximately). The commercial unit of electrical energy is the kilowatt-hour (kWh), also called one "unit", and 1 kWh equals 3.6 x 10 to the power 6 J. Electricity bills are in kWh, which is energy, not power.

Simple machines such as the lever, pulley and inclined plane reduce the effort needed but never reduce the work. They trade force against distance. Mechanical advantage is load divided by effort. Typical energy conversions: a dynamo changes mechanical energy into electrical energy, a microphone changes sound to electrical energy, a loudspeaker does the opposite, and a solar cell changes light to electrical energy.

3. Light

Light travels in a straight line in a uniform medium, and its speed in vacuum is about 3 x 10 to the power 8 m/s, the maximum possible speed. Reflection obeys two laws: the angle of incidence equals the angle of reflection, and the incident ray, reflected ray and normal lie in the same plane. A plane mirror forms a virtual, erect image of the same size, as far behind the mirror as the object is in front, with lateral inversion.

Spherical mirrors: a concave mirror converges light and a convex mirror diverges it. The focal length is half the radius of curvature, f = R/2. The mirror formula is 1/v + 1/u = 1/f, and magnification is m = -v/u, using the Cartesian sign convention in which distances are measured from the pole and distances along the incident direction are positive. A concave mirror is used in shaving mirrors, doctors' head mirrors, torches and headlights, and solar furnaces. A convex mirror is used as the rear-view mirror of vehicles because it gives an erect, diminished image with a wide field of view.

Refraction is the bending of light as it passes from one medium to another because its speed changes. Light bends towards the normal when it enters a denser medium. Snell's law states that sin i / sin r is constant for a given pair of media, and that constant is the refractive index. The refractive index of a medium equals the speed of light in vacuum divided by the speed in the medium, and it has no unit. Diamond has a very high refractive index of about 2.42, which is why it sparkles.

Lenses: a convex lens is converging and a concave lens is diverging. The lens formula is 1/v - 1/u = 1/f. The power of a lens is P = 1/f with f in metres, and the unit is the dioptre (D). A convex lens has positive power and a concave lens has negative power. A lens of focal length 50 cm has a power of +2 D.

The human eye forms a real, inverted image on the retina. The cornea does most of the refraction; the lens adjusts the focal length, a process called accommodation. The near point for a normal eye is about 25 cm and the far point is infinity. Myopia (short-sightedness) is corrected with a concave lens and hypermetropia (long-sightedness) with a convex lens. Presbyopia comes with age and bifocal lenses help. Cataract is the clouding of the eye lens and is treated surgically.

Natural phenomena: a rainbow forms by dispersion, refraction and internal reflection in water drops, with violet bending most and red least. The sky appears blue because of scattering of shorter wavelengths, and the sun appears red at sunrise and sunset because the blue is scattered away over the long path. Danger signals use red because it is scattered the least. Twinkling of stars is due to atmospheric refraction.

4. Sound

Sound is a mechanical wave that needs a material medium, so it cannot travel in vacuum. In air it travels as longitudinal waves of compressions and rarefactions. Light waves are transverse, while sound in air is longitudinal. Speed of sound is greatest in solids, less in liquids and least in gases, and it rises with temperature. In air at room temperature it is about 340 to 346 m/s, depending on the temperature quoted in the book, so read the value given in the question.

Frequency is the number of oscillations per second, with the unit hertz (Hz). Wave speed v = frequency x wavelength. Amplitude decides loudness, measured in decibels (dB), while frequency decides pitch. Quality or timbre lets us tell two instruments apart even when pitch and loudness are the same. The audible range for humans is about 20 Hz to 20,000 Hz. Below 20 Hz is infrasound (used by elephants and whales, also produced by earthquakes) and above 20,000 Hz is ultrasound (used by bats and dolphins).

An echo is the reflection of sound heard distinctly, which needs a minimum distance of about 17 m between the source and the reflector, because the ear retains a sound for about 0.1 second. Reverberation is the persistence of sound because of repeated reflection, which is reduced in auditoriums with curtains and rough walls. Worked example: a sound takes 4 seconds to return from a cliff; with a speed of 340 m/s, the total distance is 1360 m and the cliff is 680 m away.

Ultrasound applications include sonar (SOund Navigation And Ranging) for depth and submarine detection, medical ultrasonography, cleaning of delicate parts and detecting cracks in metal blocks. Noise above about 80 dB is considered harmful over long exposure.

5. Electricity and magnetism

Electric charge is measured in coulombs (C); an electron carries a charge of about 1.6 x 10 to the power minus 19 C. Current is the rate of flow of charge, I = Q/t, with the unit ampere (A), measured by an ammeter connected in series. Potential difference is the work done per unit charge, V = W/Q, with the unit volt (V), measured by a voltmeter connected in parallel. By convention current flows from the positive to the negative terminal, opposite to the drift of electrons.

Ohm's law states that at constant temperature the current through a conductor is proportional to the potential difference across it, V = IR. The unit of resistance is the ohm, shown by the Greek letter omega. Resistance of a wire is R = rho L / A, where rho is the resistivity of the material. It increases with length and decreases with area of cross section. Metals such as silver and copper have low resistivity, while alloys such as nichrome, constantan and manganin have higher resistivity and hence are used in heating elements and standard resistors.

In series, the same current passes through all resistors and the total resistance is the sum of the individual values. In parallel, the voltage is the same across each and the reciprocal of total resistance is the sum of the reciprocals. Household circuits are wired in parallel so that each appliance gets the same voltage and works independently. Worked example: 4 ohm and 4 ohm in parallel give 2 ohm; the same two in series give 8 ohm.

Heating effect: H = I squared R t (Joule's law). Electric power P = VI = I squared R = V squared / R. The fuse wire is made of a low-melting alloy and is connected in series with the live wire; it melts when too much current flows. The earth wire (green insulation, connected to a metal plate buried in the ground) protects against shocks from metal-bodied appliances. Domestic supply in India is 220 V at 50 Hz alternating current. Standard colours are red for live, black for neutral and green for earth in the newer code.

Magnetism: a magnet has two poles, like poles repel and unlike poles attract, and a freely suspended bar magnet points along north-south. Field lines emerge from the north pole and enter the south pole outside the magnet, never cross, and are closer where the field is stronger. Oersted showed in 1820 that a current-carrying wire deflects a compass needle. The direction of the field around a straight wire is given by the right-hand thumb rule. A solenoid carrying current behaves like a bar magnet, and with a soft iron core it becomes an electromagnet.

Force on a current-carrying conductor in a magnetic field is given by Fleming's left-hand rule: thumb for force, forefinger for field, middle finger for current. This is the principle of the electric motor, which converts electrical energy to mechanical energy. Electromagnetic induction, discovered by Faraday, produces current when the magnetic flux linked to a coil changes; its direction is given by Fleming's right-hand rule, and this is the principle of the generator (dynamo). A generator changes mechanical to electrical energy, a motor does the reverse, and a transformer changes the voltage of alternating current only.

Device	Principle	Energy change
Electric motor	Force on conductor in field	Electrical to mechanical
Generator	Electromagnetic induction	Mechanical to electrical
Transformer	Mutual induction	Same power, changed voltage
Electric heater	Joule heating	Electrical to heat
Fuse	Joule heating	Breaks the circuit

6. Heat

Heat is a form of energy that flows from a hotter body to a colder one; temperature is the degree of hotness. The SI unit of heat is the joule, and the older unit is the calorie (1 cal is about 4.18 J). The SI unit of temperature is the kelvin, and K = degrees Celsius + 273 (273.15 in strict terms). Water freezes at 0 degrees C (273 K) and boils at 100 degrees C (373 K) at normal pressure. The Celsius to Fahrenheit conversion is F = (9/5) C + 32, and the two scales read the same at minus 40. The clinical thermometer reads from about 35 to 42 degrees C, and normal body temperature is about 37 degrees C (98.6 degrees F).

Heat transfer happens in three ways. Conduction occurs in solids through particle vibration without the movement of the material, convection occurs in liquids and gases through the movement of the fluid itself, and radiation needs no medium, which is how the Sun's heat reaches us. Metals are good conductors; air, wood and wool are poor conductors, which is why a woollen cloth keeps you warm by trapping air. Dark surfaces absorb and emit radiation better, so we prefer light-coloured clothes in summer. A thermos flask reduces all three modes of loss.

Specific heat capacity is the heat required to raise the temperature of 1 kg of a substance by 1 K, and Q = m c delta T. Water has a very high specific heat, about 4200 J/kg K, which is why coastal areas have a moderate climate and why water is used as a coolant. Latent heat is the heat absorbed or released during a change of state without any change of temperature, so the temperature stays constant while ice melts or water boils. Steam at 100 degrees C causes a worse burn than boiling water at 100 degrees C because it carries the extra latent heat of vaporisation. Evaporation cools because the fastest molecules leave, and it takes place at all temperatures and only at the surface, while boiling takes place at a fixed temperature throughout the liquid.

Thermal expansion: solids, liquids and gases generally expand on heating. Water is anomalous between 0 and 4 degrees C, where it contracts on heating and has its maximum density at 4 degrees C, so a lake freezes from the top and fish survive underneath.

7. Atomic structure and the periodic table

Dalton's atomic theory treated the atom as indivisible. Thomson discovered the electron and proposed the plum-pudding model. Rutherford's gold-foil experiment showed a small, dense, positively charged nucleus with the electrons around it. Bohr proposed fixed circular orbits (shells) with definite energies, labelled K, L, M and N, and electrons do not radiate energy while in a shell. Chadwick discovered the neutron in 1932.

The proton has a charge of +1 and a mass of about 1 atomic mass unit, the neutron is neutral with a similar mass, and the electron has a charge of -1 with a mass about 1/1836 of a proton. The atomic number Z is the number of protons, the mass number A is protons plus neutrons, and so the neutrons equal A minus Z. Isotopes have the same atomic number but different mass numbers (chlorine-35 and chlorine-37; hydrogen has protium, deuterium and tritium; carbon-14 is used in dating and iodine-131 in thyroid treatment). Isobars have the same mass number but different atomic numbers (argon-40 and calcium-40). The maximum electrons in a shell is 2n squared: 2, 8, 18 and 32. The outermost shell holds at most 8 electrons (the octet rule), except the first shell, which holds 2.

The periodic table has evolved. Dobereiner's triads and Newlands' law of octaves were early attempts. Mendeleev arranged elements by increasing atomic mass and left gaps for undiscovered elements, such as eka-aluminium (gallium) and eka-silicon (germanium). The Modern Periodic Law, after Moseley, says the properties of elements are a periodic function of their atomic number. The modern table has 18 groups (vertical columns) and 7 periods (horizontal rows), and 118 elements are known. Group 1 elements are alkali metals, group 2 alkaline earth metals, group 17 halogens and group 18 noble gases (inert, with complete outer shells). Across a period from left to right, atomic size decreases, the metallic character falls and the non-metallic character rises. Down a group, size and metallic character increase. Valency equals the number of valence electrons for groups 1 to 4 and 8 minus that number after. Trap: Mendeleev used atomic mass, the modern table uses atomic number.

8. Acids, bases and salts

Acids taste sour, turn blue litmus red, and give hydrogen ions (hydronium) in water. Bases taste bitter, feel soapy, turn red litmus blue, and those that dissolve in water are called alkalis. Natural indicators include litmus, turmeric (turns red with a base) and red cabbage; olfactory indicators include onion and vanilla. Phenolphthalein is colourless in acid and pink in a base, while methyl orange is red in acid and yellow in a base.

The pH scale runs from 0 to 14 and measures hydrogen ion concentration; pH 7 is neutral, below 7 is acidic and above 7 is basic. Lower pH means stronger acidity. Examples: gastric juice about 1.2, lemon juice about 2.2, tomato juice about 4, pure water 7, blood about 7.4, baking soda solution about 8, milk of magnesia about 10 and sodium hydroxide about 14. Tooth enamel is calcium phosphate and starts corroding below about pH 5.5, so toothpaste is basic. The soil pH decides crop suitability, and acid rain has a pH below 5.6.

Common reactions: acid plus metal gives salt plus hydrogen; acid plus metal carbonate or hydrogencarbonate gives salt, water and carbon dioxide; acid plus base gives salt plus water (neutralisation). Limewater turns milky with carbon dioxide because calcium carbonate forms. Natural sources: citric acid in lemon, tartaric acid in tamarind, lactic acid in curd, oxalic acid in spinach and tomato, formic (methanoic) acid in ant and nettle stings, and acetic acid in vinegar. Antacids such as milk of magnesia treat acidity, and baking soda paste is rubbed on a sting.

Salts and their uses: sodium chloride (common salt) is the starting point for the chlor-alkali process, producing sodium hydroxide, chlorine and hydrogen by the electrolysis of brine. Sodium hydrogencarbonate (baking soda, NaHCO3) is used in baking powder (with tartaric acid), in antacids and in soda-acid fire extinguishers. Sodium carbonate decahydrate (washing soda, Na2CO3.10H2O) is used for washing and removing the hardness of water. Bleaching powder (CaOCl2) is made by passing chlorine over slaked lime and is used for disinfecting drinking water and bleaching cotton. Plaster of Paris is calcium sulphate hemihydrate (CaSO4.1/2 H2O), made by heating gypsum (CaSO4.2H2O) at about 373 K, and it is used for supporting fractured bones and making toys. Water of crystallisation is the fixed number of water molecules in a salt crystal; copper sulphate pentahydrate is blue and turns white when heated and the water leaves.

Traps: baking soda and washing soda are different compounds, with different formulae. Neutralisation does not always give a pH of exactly 7: a strong acid with a weak base gives an acidic salt solution.

9. Metals and non-metals

Metals are lustrous, malleable, ductile and good conductors of heat and electricity, and they usually have high melting points. Exceptions: mercury is a liquid metal at room temperature; sodium and potassium are soft and can be cut with a knife; gallium and caesium melt at a very low temperature; lead and mercury are poor conductors compared to silver. Non-metals are generally brittle and non-conducting, but graphite conducts electricity and diamond is the hardest natural substance. Iodine is lustrous though it is a non-metal, and bromine is the only liquid non-metal.

Reactivity series, from most to least reactive: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, mercury, silver, gold. A more reactive metal displaces a less reactive one from its salt solution (iron nail in copper sulphate turns brown with copper deposition and the blue colour fades). Sodium and potassium are stored under kerosene because they react vigorously with air and water. Metals above hydrogen displace hydrogen from dilute acids. Aqua regia is a 3:1 mixture of concentrated hydrochloric and nitric acids that can dissolve gold and platinum.

Metals combine with oxygen to form basic oxides, and aluminium oxide and zinc oxide are amphoteric oxides because they react with both acids and bases. Non-metal oxides are acidic or neutral (carbon monoxide, water). Ionic compounds are formed by the transfer of electrons from metal to non-metal, have high melting points, are hard and brittle, dissolve in water and conduct electricity in the molten or dissolved state only.

Extraction depends on reactivity. Highly reactive metals (sodium, calcium, aluminium) are obtained by electrolysis of the molten compound. Middle metals (zinc, iron, lead) are obtained from their oxides by reduction with carbon after roasting or calcination. Low-reactivity metals (mercury from cinnabar, copper) are obtained by heating the sulphide ore and gold and silver occur in the native state. The thermit reaction uses aluminium to reduce iron oxide and produces molten iron to weld railway tracks. Electrolytic refining gives pure copper at the cathode.

Corrosion is the slow attack on a metal by air and moisture. Rusting of iron needs both oxygen and water, and is prevented by painting, oiling, galvanisation (coating with zinc), chrome plating and making alloys. Silver tarnishes black because of sulphur compounds, and copper develops a green coating of basic copper carbonate. An alloy is a homogeneous mixture of metals or of a metal with a non-metal: brass is copper and zinc, bronze is copper and tin, solder is lead and tin, and stainless steel is iron with chromium and nickel. Pure gold (24 carat) is too soft for jewellery, so it is alloyed with copper or silver. An amalgam is an alloy with mercury.

10. Carbon compounds

Carbon has four valence electrons and forms covalent bonds by sharing electrons. Two properties explain its enormous number of compounds: catenation (self-linking into chains, branches and rings) and tetravalency. Covalent compounds generally have low melting and boiling points and poor electrical conductivity because no ions exist.

Allotropes: diamond (each carbon bonded to four others in a rigid lattice, hardest, an electrical insulator), graphite (layers of hexagons, soft and slippery, a conductor, used in pencils and as a lubricant) and fullerenes (C-60, shaped like a football, named after Buckminster Fuller). Hydrocarbons with only single bonds are saturated (alkanes, general formula CnH2n+2) and those with a double or triple bond are unsaturated (alkenes CnH2n and alkynes CnH2n-2). Methane CH4, ethane C2H6, propane C3H8 and butane C4H10 are the first four alkanes; ethene C2H4 and ethyne C2H2 are the first alkene and alkyne. A homologous series is a family of compounds with the same functional group and differing by a CH2 unit, with a regular gradation in physical properties.

Functional groups: alcohol (-OH, as in ethanol), aldehyde (-CHO), ketone (C=O in the chain), carboxylic acid (-COOH, as in ethanoic acid) and halo (-Cl, -Br). Ethanol is formed by fermenting sugars with yeast, is used as a solvent and in medicines such as tonics, and is the main part of rectified spirit. Denatured alcohol has poisonous additives such as methanol and dye. Methanol is poisonous and can cause blindness. Ethanoic (acetic) acid is the main part of vinegar, which is a 5 to 8 per cent solution in water, and pure ethanoic acid freezes at about 290 K, hence it is called glacial. Ethanol with ethanoic acid in the presence of concentrated sulphuric acid gives an ester, ethyl ethanoate (esterification), which has a sweet fruity smell. Saponification is the alkaline hydrolysis of an ester (a fat or oil) to produce soap.

Reactions: combustion (burning in oxygen to give carbon dioxide, water, heat and light), oxidation (alcohols to acids with an oxidising agent such as alkaline potassium permanganate), addition (unsaturated compounds react with hydrogen in the presence of nickel or palladium catalyst, as in making vegetable ghee from oil) and substitution (saturated hydrocarbons react with chlorine in sunlight). Saturated hydrocarbons burn with a clean blue flame, and unsaturated ones burn with a yellow sooty flame because of incomplete combustion.

Soaps are sodium or potassium salts of long-chain fatty acids. A soap molecule has a hydrophilic head and a hydrophobic tail, and it forms micelles that trap oily dirt. In hard water, which contains calcium and magnesium salts, soap forms an insoluble scum, while detergents (usually sodium salts of sulphonic acids) lather in hard water also.

11. Everyday chemistry

Chemical change produces a new substance (rusting, burning, curdling of milk, cooking, ripening of fruit) while a physical change does not (melting of ice, dissolving of sugar, boiling of water). Types of reactions: combination (burning of quicklime with water to give slaked lime with the release of heat), decomposition (heating limestone to get quicklime and carbon dioxide), displacement, double displacement (precipitation of white barium sulphate) and redox. Oxidation is the gain of oxygen or the loss of hydrogen and reduction is the opposite, and the two always occur together. Rancidity is the oxidation of fats and oils in food, delayed by adding antioxidants, flushing a pack with nitrogen and refrigeration.

Water hardness is caused by dissolved calcium and magnesium salts. Temporary hardness is due to bicarbonates and is removed by boiling, while permanent hardness is due to chlorides and sulphates and is removed by washing soda or by ion exchange. Fertilisers supply nitrogen, phosphorus and potassium (NPK). Urea has the highest nitrogen content among the common fertilisers, about 46 per cent. Cement and glass: cement is mainly made from limestone and clay, and gypsum is added to slow its setting. Glass is made by fusing sand with soda and limestone. Fuels are rated by their calorific value, the heat produced by complete burning of a unit mass, in kJ per kg. LPG is mainly butane, and CNG is mainly methane. Hydrogen has the highest calorific value among common fuels.

Common names matter: quicklime is calcium oxide, slaked lime is calcium hydroxide, limestone is calcium carbonate, caustic soda is sodium hydroxide, caustic potash is potassium hydroxide, blue vitriol is copper sulphate pentahydrate, green vitriol is iron sulphate heptahydrate, and dry ice is solid carbon dioxide. Greenhouse gases include carbon dioxide, methane, nitrous oxide and water vapour, and chlorofluorocarbons deplete the ozone layer, which shields the Earth from ultraviolet radiation.

Common traps at a glance

• Mass is in kilograms and does not change with place, weight is in newtons and changes.
• Velocity-time graph area is displacement, slope is acceleration.
• Work is zero when displacement is zero or perpendicular to the force.
• kWh is a unit of energy, not power.
• Sound needs a medium, light does not; sound is fastest in solids.
• Concave lens and concave mirror differ: a concave lens diverges, a concave mirror converges.
• Ammeter in series, voltmeter in parallel.
• Mendeleev: atomic mass; modern law: atomic number.
• Baking soda NaHCO3, washing soda Na2CO3.10H2O; bleaching powder CaOCl2; plaster of Paris CaSO4.1/2 H2O.
• Diamond is an insulator, graphite is a conductor, both are pure carbon.
• Steam burns worse than boiling water at the same temperature, because of latent heat.

Key facts for exams

• SI base units include metre, kilogram, second, ampere, kelvin, mole and candela.
• Speed of light in vacuum: about 3 x 10 to the power 8 m/s.
• Audible range: 20 Hz to 20 kHz.
• Domestic supply in India: 220 V, 50 Hz.
• Power of a lens in dioptres: 1 divided by focal length in metres.
• Number of elements: 118; groups 18; periods 7.
• Reactivity order begins K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.
• Only mercury (metal) and bromine (non-metal) are liquids at room temperature.
• General formula of alkanes CnH2n+2, alkenes CnH2n, alkynes CnH2n-2.
• pH below 7 acidic, 7 neutral, above 7 basic.

10 practice MCQs

1. A body moves along a circle of radius r and completes one full circle. Its displacement is (a) 2 pi r (b) pi r (c) zero (d) r Answer: (c). The start and end points coincide, so the shortest change of position is zero.

2. A car starting from rest has a uniform acceleration of 2 m/s squared. Its distance in 5 seconds is (a) 10 m (b) 25 m (c) 50 m (d) 5 m Answer: (b). s = half x 2 x 25 = 25 m.

3. The kinetic energy of a moving body becomes how many times when its speed is doubled? (a) 2 (b) 4 (c) 8 (d) 1/2 Answer: (b). Kinetic energy depends on the square of speed.

4. The power of a lens with focal length 25 cm is (a) +4 D (b) -4 D (c) +0.25 D (d) +25 D Answer: (a). P = 1 / 0.25 m = +4 D, and a convex lens has positive power.

5. Which of these cannot travel through a vacuum? (a) Light (b) Radio waves (c) Sound (d) X-rays Answer: (c). Sound is a mechanical wave and needs a medium.

6. Two resistors of 6 ohm each are connected in parallel. The total resistance is (a) 12 ohm (b) 6 ohm (c) 3 ohm (d) 1 ohm Answer: (c). 1/R = 1/6 + 1/6 = 1/3.

7. Isotopes of an element have the same (a) mass number (b) number of neutrons (c) atomic number (d) both (a) and (b) Answer: (c). They differ in the neutron count and hence mass number.

8. The chemical formula of plaster of Paris is (a) CaSO4.2H2O (b) CaSO4.1/2 H2O (c) CaOCl2 (d) Na2CO3.10H2O Answer: (b). Gypsum is (a), bleaching powder is (c) and washing soda is (d).

9. A solution has a pH of 3. It is (a) strongly basic (b) neutral (c) weakly basic (d) acidic Answer: (d). Any pH below 7 is acidic.

10. The general formula of the alkane series is (a) CnH2n (b) CnH2n+2 (c) CnH2n-2 (d) CnHn Answer: (b). Methane CH4 is n = 1: 2 x 1 + 2 = 4.

Frequently asked questions

Which classes' books should I read for general science? For APPSC, DSC and Police papers, the content of Classes 6 to 10 is enough for most questions. DSC candidates should also read the SCERT Andhra Pradesh textbooks, because the content method questions are built on them.

How much time should physics and chemistry take? Many aspirants complete one revision of this material in about two weeks of daily one-hour sessions and then switch to practising questions. Adjust to your own level.

Do I need to memorise numerical formulae? Yes, the 15 to 20 formulae in this note, with their units. Most numerical questions need one step of substitution.

Are SI units asked directly? Frequently. Know the unit and the type (scalar or vector) for each quantity.

Is the periodic table asked in detail? Usually only the groups, periods, trends, the number 118 and the names of group families. Do not memorise all the atomic masses.

What is the best way to handle chemical formulae? Learn them in pairs with the common name (for example baking soda and NaHCO3) and revise them with a table.

Will new editions of NCERT change these facts? The laws and units are stable. Chapter names and arrangement change between editions, so rely on the concept and not on the chapter number.

Related reading

• Andhra Pradesh GK: top 100 questions
• AP DSC syllabus 2026
• AP Police Constable guide
• AP Sachivalayam Secretary guide
• APPSC Group 2 prelims 90-day plan
• Negative marking and mock strategy
• General science biology and health notes
• Telugu version of this post

Practise on pareeksha.in

After one reading, test yourself on science topic tests and a mock test, where the platform offers 10 Lakh+ MCQs, 100+ Exams and 5,000+ Full-Length Mocks. Keep a short notebook of the questions you miss and return to the matching section above.

Sources and verification

Pages opened for this revision:

• NCERT Science textbook for Class 10 (reprint 2026-27), chapters 1 to 4 and 9 to 13 (ncert.nic.in): reactivity series, pH, salts, carbon compounds, light, electricity, magnetism and environment, including Ohm's law, Fleming's rules, mirror formula and the ozone layer.
• NCERT Science textbook for Class 9 (2026-27 edition), chapters 4, 6, 7 and 9 (ncert.nic.in), used for the motion, force, work and atomic-structure framing.

Not verified and hedged in the text: the exact speed of sound in air (varies with temperature and book), the vinegar concentration range and the freezing point of glacial ethanoic acid (read from standard NCERT statements, not re-opened line by line), the urea nitrogen percentage, the calorific-value ranking of fuels, the 0.1-second persistence-of-hearing figure, the colour code for house wiring, and the new Class 9 chapter titles. For any exam-specific syllabus point, check the latest notification.