General Science
General Science at constable level is Class 8–10 physics, chemistry and biology, usually applied to everyday observations and the human body rather than to derivations.
Physics
- SI base units: metre, kilogram, second, ampere, kelvin, mole, candela.
- Speed = distance/time; convert km/h to m/s by multiplying by 5/18.
- Force F = ma; weight = mg, so weight changes with location while mass does not.
- Light: reflection keeps the angle of incidence equal to the angle of reflection; light entering a denser medium bends towards the normal.
- Ohm's law V = IR; household appliances are wired in parallel so each receives full supply voltage.
Chemistry
- pH below 7 is acidic, above 7 basic; acids turn blue litmus red.
- Recognise common formulas: CO2, NaCl, CaCO3 (limestone), NaHCO3 (baking soda), H2SO4.
Biology
- Deficiency mapping: vitamin A - night blindness; B1 - beriberi; C - scurvy; D - rickets; iodine - goitre; iron - anaemia.
- Blood group O negative is the universal donor; AB positive the universal recipient.
- Photosynthesis: 6CO2 + 6H2O in the presence of light and chlorophyll gives glucose and oxygen.
Worked example
A person of mass 60 kg stands in a lift accelerating upward at 2 m/s². What is the apparent weight? Reasoning: the floor supports the weight plus the extra force needed for upward acceleration, so N = m(g + a) = 60 × (9.8 + 2) = 708 N, more than the normal 588 N. In a lift accelerating downward, N = m(g − a) and the person feels lighter.
Traps
- Giving weight in kilograms; weight is a force measured in newtons.
- Mixing deficiency diseases under exam pressure - revise the vitamin table as pairs, not as a list.
- Assuming a body in uniform motion needs a continuous force.