General Science - Physics, Chemistry and Biology
Scope
The science section asks class-8-to-10 level concepts, not derivations: units and measurement, motion, force, light, electricity, acids and bases, metals, chemical formulae, the human body, nutrition, plant physiology and basic ecology.
Physics essentials
- SI units: metre, kilogram, second, ampere, kelvin, mole, candela.
- Speed is scalar, velocity vector; acceleration = change in velocity/time; 1 newton = 1 kg·m/s².
- Light travels fastest in vacuum; convex lens converges, concave diverges; a plane mirror forms a virtual, laterally inverted image.
- Ohm's law: V = IR; power P = VI.
Chemistry essentials
- pH below 7 is acidic, above 7 basic; litmus turns red in acid.
- Common formulae: H₂O, CO₂, NaCl, CaCO₃ (limestone), NaHCO₃ (baking soda), H₂SO₄.
- Metals are malleable and ductile; mercury is liquid at room temperature; sodium is stored in kerosene.
Biology essentials
- Cell is the structural unit; mitochondria release energy, chloroplasts carry out photosynthesis.
- Human body: 206 bones in an adult, four-chambered heart, lungs for gaseous exchange, nephrons in kidneys.
- Deficiency diseases: vitamin A night blindness, vitamin C scurvy, iron anaemia, iodine goitre.
Worked example
A body covers 60 km in 2 hours and another 90 km in 3 hours. Total distance = 150 km, total time = 5 h, so average speed = 30 km/h - not (30 + 30)/2 written blindly; here both legs are 30 km/h, which is why the short method appears to work.
Traps
Confusing mass with weight; mixing average speed with average velocity; naming baking soda as washing soda; claiming the heart has three chambers in adults.