Every key fact, concept and formula from the Class 8 Science NCERT syllabus (Curiosity), organised by chapter. Cross-linked to our full Chapter-wise Solutions. More chapters will be appended here as their Solutions are published.
Class 8 Science Formulas Handbook
Chapter 1: Exploring the Investigative World of Science
- Steps of scientific investigation: question → design experiment (identify variables) → change one variable at a time → observe/measure → conclude
- Variable: a factor you can deliberately change or control in an experiment (e.g. dough thickness, oil temperature)
- Observation/measurement: the outcome you record to test the effect of a variable (e.g. whether the puri puffs, time taken to puff)
- Systematic investigation: testing only one variable at a time while holding all others constant, so results can be clearly attributed to a single cause
- See full Chapter 1 Solutions
Chapter 2: The Invisible Living World
- Cell structures: cell membrane (entry/exit control), cytoplasm (life processes), nucleus (controls activities/growth), cell wall (plant/fungal/bacterial), nucleoid (bacteria only, no true nucleus)
- Organisation: Cell → Tissue → Organ → Organ system → Organism
- Yeast: ferments sugar → releases CO2 + alcohol (bread/cake rising)
- Lactobacillus: ferments lactose → lactic acid (curd formation)
- Rhizobium: fixes atmospheric nitrogen in legume root nodules
- Preservation: high salt/sugar draws water out of microbial cells by osmosis, preventing spoilage
- See full Chapter 2 Solutions
Chapter 3: Health The Ultimate Treasure
- Health (WHO): complete physical, mental and social well-being, not just absence of disease
- Communicable diseases: spread person-to-person (flu, typhoid, chickenpox, cholera)
- Non-communicable diseases: not transmissible (diabetes, asthma, heart disease)
- Primary immune response: slow, first exposure; Secondary: fast, memory-cell based, on re-exposure
- Antibiotics: effective against bacteria only, not viruses
- See full Chapter 3 Solutions
Chapter 4: Electricity Magnetic and Heating Effects
- Magnetic effect: current-carrying wire produces a magnetic field (Oersted, 1820)
- Electromagnet: coil + current = temporary magnet; strength up with more current, more turns, iron core
- Heating effect: current through resistance generates heat
- Nichrome: higher resistance than copper, used in heating elements
- Voltaic cell: chemical reaction between two metal electrodes + electrolyte generates current
- See full Chapter 4 Solutions
Chapter 5: Exploring Forces
- Force: SI unit newton (N); push or pull from interaction between two objects
- Contact forces: muscular force, friction
- Non-contact forces: magnetic, electrostatic, gravitational
- Weight = gravitational force on an object (varies by location); Mass = fixed amount of matter (constant everywhere)
- Buoyant force = weight of liquid displaced (Archimedes’ Principle); floats if buoyant force ≥ weight
- See full Chapter 5 Solutions
Chapter 6: Pressure, Winds, Storms and Cyclones
- Pressure = Force ÷ Area; SI unit pascal (Pa) = N/m2
- Liquid pressure increases with the height/depth of the liquid column, independent of the container’s shape or width
- Wind: air flowing from a high-pressure region to a low-pressure region
- Sea breeze (day): land heats faster than sea, creating low pressure over land; cooler air flows from sea to land
- Thunderstorm: rising warm moist air → condensation → charge separation between ice (+) and water droplets (−) → lightning (discharge) and thunder (rapid air expansion)
- Cyclone: intensifies over warm ocean water; very low-pressure centre (the “eye”) is calm, surrounded by a ring of the highest wind speeds
- See full Chapter 6 Solutions
Chapter 7: Particulate Nature of Matter
- All matter is made of tiny particles too small to see individually; breaking/grinding a substance is a physical change, not a chemical one
- Solids: particles closely packed in fixed positions, only vibrate; fixed shape and fixed volume
- Liquids: particles close together but free to move/slide past each other; fixed volume, no fixed shape (takes container’s shape)
- Gases: particles far apart, move fast and randomly; no fixed shape or volume
- Interparticle attraction: strongest in solids, weaker in liquids, weakest in gases
- Dissolving: solute particles fit into the gaps between solvent particles (physical change); differs from a substance like sand that doesn’t break down and simply settles
- Sublimation: solid changes directly to gas without becoming liquid first, e.g. camphor, dry ice
- See full Chapter 7 Solutions
Chapter 8: Nature of Matter – Elements, Compounds and Mixtures
- Element: only one kind of atom; cannot be broken down chemically (e.g. gold, oxygen, hydrogen).
- Compound: two+ elements chemically combined in a fixed ratio; new properties (e.g. water, CO2, NaCl, FeS).
- Mixture: substances physically combined in variable proportions; separable by physical means.
- Homogeneous mixture: uniform composition throughout (air, salt water, alloys).
- Heterogeneous mixture: visibly distinct parts (sand+water, muddy water).
- Electrolysis of water: H2O -> H2 + O2 in 2:1 ratio, proves water is a compound.
- Test for CO2: turns lime water milky (forms CaCO3).
See full Chapter 8 Solutions.
Chapter 9: The Amazing World of Solutes, Solvents and Solutions
- Solution: uniform mixture of solute (smaller amount) + solvent (larger amount).
- Suspension: non-uniform mixture, particles settle (e.g. sand+water) — NOT a solution.
- Solubility: max solute that dissolves in a fixed amount of solvent at a given temperature.
- Saturated solution: no more solute can dissolve at that temperature.
- Solids: solubility usually increases with temperature. Gases: solubility decreases with temperature.
- Volume of regular solids = length x width x height.
- Volume of irregular solids: water-displacement method (1 mL displaced = 1 cm^3).
- Density = Mass / Volume. Object floats if its density < liquid’s density.
See full Chapter 9 Solutions.
Chapter 10: Light: Mirrors and Lenses
- Laws of reflection: angle of incidence = angle of reflection; incident ray, reflected ray and normal lie in the same plane.
- Plane mirror: virtual, erect, same-size image; image distance behind mirror = object distance in front.
- Concave mirror: can form real or virtual images, enlarged or diminished, depending on object distance.
- Convex mirror: always virtual, erect, diminished image; wider field of view than plane mirror; image grows larger as object approaches.
- Convex lens: converges light; can form magnified virtual image (object close) or real inverted image (object far).
- Concave lens: diverges light; always forms virtual, erect, diminished image, regardless of object distance.
- Refraction: light bends when passing between media of different density (e.g. bent-pencil-in-water effect).
See full Chapter 10 Solutions.
Chapter 11: Keeping Time with the Skies
- Day = Earth’s rotation (~24 hours). Month = Moon’s revolution (~29.5 days synodic, ~27.3 days sidereal). Year = Earth’s revolution around Sun (~365.25 days).
- Moon phases are caused by how much of its sunlit half faces Earth, not by Earth’s shadow (that’s a lunar eclipse).
- Tidal locking: Moon’s rotation period = orbital period, so same face always faces Earth.
- Luni-solar calendars add an intercalary month periodically since 12 lunar months (~354 days) fall ~11 days short of a solar year.
- Leap year: extra day added roughly every 4 years.
- Geostationary satellite: orbital period = 24 hours, matching Earth’s rotation, so it stays above the same ground point.
See full Chapter 11 Solutions.
Chapter 12: How Nature Works in Harmony
- Population: all individuals of one species in an area. Community: all populations of different species in an area. Ecosystem: community + non-living (abiotic) environment.
- Food chain: straight-line sequence of who-eats-whom. Food web: network of overlapping food chains — more stable than a single chain.
- Trophic level: an organism’s position in a food chain (producer = 1st, herbivore = 2nd, carnivore = 3rd+).
- Producers make their own food (photosynthesis); consumers eat other organisms; decomposers break down dead matter and recycle nutrients.
- Ecological pyramid: numbers/biomass decrease at each higher trophic level (roughly 10% energy transfer between levels).
- Removing a species affects both the trophic level below (less predation) and above (less food) — effects ripple through the food web.
- Mangrove forests buffer coastlines against storms/tsunamis and provide marine breeding habitat.
See full Chapter 12 Solutions.
Chapter 13: Our Home: Earth, A Unique Life Sustaining Planet
- Habitable zone: region around a star where temperatures allow liquid water; Earth’s ~150 million km distance places it here.
- Atmosphere: nitrogen/oxygen mix supports breathing, ozone layer blocks UV, greenhouse effect regulates temperature.
- Magnetic field: shields atmosphere from solar wind erosion.
- Plate tectonics: recycles nutrients, drives long-term carbon cycle, stabilises climate.
- Size/gravity balance: too small → atmosphere escapes (Mars-like); too large → atmosphere traps too much heat (Venus-like).
- Geodiversity (landforms/rocks) vs biodiversity (living organisms) — related but distinct.
- Vegetative propagation: asexual reproduction from stems/roots/leaves (money plant, potato, ginger, sugarcane, bamboo).
See full Chapter 13 Solutions.
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