General Science: Physics and Chemistry

Units and measurement

Quantity	SI unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

Derived units:

• newton (force) = kg·m·s⁻²
• joule (energy) = N·m
• watt (power) = J·s⁻¹
• pascal (pressure) = N·m⁻²
• hertz (frequency) = s⁻¹
• coulomb (charge), volt, ohm (Ω)

Useful conversions:

• 1 light year ≈ 9.46 × 10¹⁵ m (a unit of distance, not time).
• 1 horsepower ≈ 746 W.
• 1 kWh = 3.6 × 10⁶ J, which is "one unit" of electricity.
• Temperature: °C = K − 273.15, and °F = (⁹⁄₅)°C + 32. −40° is the same on the Celsius and Fahrenheit scales.

Motion, force and energy

Newton's laws

• First law: inertia.
• Second law: F = ma.
• Third law: action and reaction are equal and opposite. This is how rockets work.

Momentum p = mv, and it is conserved.

Gravity

• F = G m₁m₂ / r².
• g ≈ 9.8 m/s² on the earth.
• Escape velocity from the earth is about 11.2 km/s.
• Weight is less at the equator than at the poles, because the earth bulges and rotates.

Work and energy

• Work W = F × s.
• Kinetic energy = ½mv².
• Potential energy = mgh.
• Power = work ÷ time.

Pressure and fluids

• Pressure = F/A.
• Pascal's law is used in hydraulic lifts and brakes.
• Archimedes' principle explains floating: ice floats because it is less dense than water.
• Bernoulli's principle explains aircraft lift.
• Surface tension makes water form droplets. Capillarity lets a wick draw up oil.

Heat

• Conduction, convection (sea breezes, monsoon) and radiation (sunlight).
• Water has a high specific heat, which keeps coastal climates moderate.
• Latent heat: sweating cools the body by evaporation.
• Anomalous expansion of water: water is densest at 4 °C, so lakes freeze from the top and fish survive underneath.

Light

• Reflection:
  • plane mirrors;
  • a concave mirror is used in shaving mirrors, torch reflectors and solar furnaces;
  • a convex mirror is used as a vehicle rear-view mirror because it gives a wide view.
• Refraction: a stick looks bent in water.
  • A convex lens corrects hypermetropia (long-sightedness).
  • A concave lens corrects myopia (short-sightedness).
• Total internal reflection: mirages, the sparkle of diamonds, optical fibres.
• Dispersion: a prism splits white light into VIBGYOR; rainbows form the same way.
• Scattering: the blue sky (Rayleigh scattering) and red sunsets. Danger signals are red because red scatters least.
• The speed of light is about 3 × 10⁸ m/s.

Sound

• Sound needs a medium. It travels fastest in solids and slowest in gases. It cannot pass through a vacuum.
• Audible range: 20 Hz to 20 kHz. Below that is infrasound (used by elephants and earthquake detection); above it is ultrasound (bats, SONAR, sonography).
• An echo needs a distance of at least about 17 m.
• The Doppler effect is the change in pitch as a source moves.
• Loudness is measured in decibels (dB).

Electricity and magnetism

• Ohm's law: V = IR.
• Resistors in series: R = R₁ + R₂. In parallel: 1/R = 1/R₁ + 1/R₂. Household wiring is in parallel.
• Power P = VI = I²R.
• Fuses have a low melting point. MCBs trip on overload.
• India's household supply is 220–230 V AC at 50 Hz.
• Electromagnetic induction (Faraday) is the basis of generators and transformers.
• Electric motors convert electrical energy to mechanical energy. Generators do the reverse.
• Semiconductors: silicon, diodes, transistors and LEDs. Superconductors have zero resistance at very low temperatures.

Modern physics

• Atom: protons, neutrons and electrons.
• Isotopes have the same atomic number but different mass numbers (e.g. C-12 and C-14).
• Radioactivity: alpha, beta and gamma rays. Half-life is the time for half the nuclei to decay. C-14 dating has a half-life of about 5,730 years.
• Fission splits heavy nuclei and is used in reactors and atom bombs. Fusion joins light nuclei; it powers the Sun and the hydrogen bomb, and ITER is an international fusion project in which India is a partner.
• India's three-stage nuclear programme (Bhabha): PHWRs using uranium, fast breeder reactors (Kalpakkam), and later thorium. India has large thorium reserves in monazite sands.
• The photoelectric effect (Einstein) is the basis of solar cells.

Chemistry essentials

• States of matter: solid, liquid, gas, plasma, and the Bose–Einstein condensate (S. N. Bose). Sublimation is when a solid turns straight into gas, as with camphor, naphthalene and dry ice.
• Mixtures and separation: filtration, distillation, chromatography and centrifugation (used to separate cream from milk).
• Acids, bases and salts:
  • pH below 7 is acidic and above 7 is basic. Bee stings are acidic, so baking soda helps; wasp stings are alkaline.
  • Acids in daily life: citric (lemon), acetic (vinegar), lactic (curd), tartaric (tamarind), formic (ant sting) and hydrochloric (stomach).
  • Common salts: baking soda NaHCO₃; washing soda Na₂CO₃·10H₂O; bleaching powder CaOCl₂; plaster of Paris CaSO₄·½H₂O; gypsum CaSO₄·2H₂O.
• Metals and non-metals:
  • Mercury is the only metal that is liquid at room temperature.
  • Tungsten has a high melting point and is used in bulb filaments.
  • Gold and silver are the best conductors; copper is used for wiring.
  • Alloys: brass (Cu + Zn), bronze (Cu + Sn), stainless steel (Fe + Cr + Ni), solder (Pb + Sn).
  • Corrosion and rusting are oxidation. Galvanising means coating with zinc.
• Carbon compounds:
  • Allotropes: diamond (hardest), graphite (conductor, lubricant) and graphene.
  • Hydrocarbons: LPG is butane and propane; CNG is methane.
  • Fuels: octane rating for petrol; ethanol blending (E20).
  • Polymers: polythene, PVC, nylon, Teflon.
  • Soaps and detergents.
• Everyday chemistry:
  • Chlorination of water;
  • ozonation;
  • fertilisers (urea, DAP);
  • pesticides;
  • artificial sweeteners;
  • food preservatives (sodium benzoate);
  • fire extinguishers: CO₂ for electrical fires, never water on oil fires.

Exam tip: BPSC and JPSC science questions are about class 10 level and very factual: units, defects of vision, common chemical names, pH. UPSC asks the same science through technology applications. Revise with the MCQs below and NCERT class 9–10 science.