General Science is one of the most important sections in SSC CGL, SSC CHSL, Railway and UPSC Prelims. The questions test both conceptual understanding and factual knowledge across Physics, Chemistry and Biology.
Physics: Fundamental Laws and Concepts
Newton Laws of Motion: 1st Law (Law of Inertia): An object at rest stays at rest and an object in motion stays in motion unless acted upon by an external force. 2nd Law: F = ma (Force = mass x acceleration). 3rd Law: For every action there is an equal and opposite reaction.
Thermodynamics: 1st Law: Energy cannot be created or destroyed, only converted (Law of Conservation of Energy). 2nd Law: Heat flows spontaneously from hot to cold; entropy of universe increases. 3rd Law: At absolute zero, entropy of a perfect crystal is zero.
Key Constants: Speed of light (c) = 3 x 10^8 m/s. Gravitational constant (g) = 9.8 m/s2. Planck constant (h) = 6.626 x 10^-34 J.s. Avogadro number = 6.022 x 10^23.
Electricity: Ohm Law: V = IR (Voltage = Current x Resistance). Power = VI = I2R = V2/R. Resistors in series: R_total = R1 + R2 + R3. Resistors in parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3.
Chemistry: Key Concepts
Periodic Table: 118 elements in 18 groups and 7 periods. Atomic number = number of protons. Atomic mass = protons + neutrons. Alkali metals (Group 1): Li, Na, K, Rb, Cs, Fr. Noble gases (Group 18): He, Ne, Ar, Kr, Xe, Rn.
Common Compounds: NaCl (common salt), NaOH (caustic soda/lye), Na2CO3 (washing soda), NaHCO3 (baking soda), H2SO4 (sulphuric acid - king of chemicals), HCl (hydrochloric acid), H2O2 (hydrogen peroxide).
pH Scale: pH 0-6 = acidic, pH 7 = neutral, pH 8-14 = basic/alkaline. Pure water pH = 7. Blood pH = 7.35-7.45 (slightly alkaline). Gastric juice pH = 1.5-2 (very acidic).
| Vitamin | Chemical Name | Deficiency Disease |
|---|---|---|
| Vitamin A | Retinol | Night Blindness |
| Vitamin B1 | Thiamine | Beriberi |
| Vitamin B12 | Cyanocobalamin | Pernicious Anaemia |
| Vitamin C | Ascorbic Acid | Scurvy |
| Vitamin D | Calciferol | Rickets (children) |
| Vitamin K | Phylloquinone | Excessive Bleeding |
Biology: Human Body Systems
Digestive System: Digestion begins in mouth with saliva (amylase). Stomach secretes HCl and pepsin. Small intestine (ileum) is main site of nutrient absorption. Liver produces bile for fat emulsification. Pancreas secretes digestive enzymes and insulin.
Circulatory System: Heart has 4 chambers (2 atria + 2 ventricles). Double circulation: pulmonary (heart-lungs-heart) and systemic (heart-body-heart). Blood groups: A, B, AB, O. Rh factor positive/negative. O- is universal donor; AB+ is universal recipient.
Cell Biology: Cell is the basic unit of life (Robert Hooke coined cell in 1665). Cell theory: all living things made of cells; cells arise from pre-existing cells. Mitochondria = powerhouse (ATP production). Ribosome = protein synthesis. Chloroplast = photosynthesis (only in plants).
Genetics: DNA (Deoxyribonucleic Acid) carries genetic information. Gene is a segment of DNA that codes for a protein. Chromosomes: humans have 46 (23 pairs). Sex chromosomes: XX = female, XY = male. Mendel Laws of Inheritance discovered using pea plants.