General Science

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

General Science — Quick Facts for SSC CGL

Physics:

Laws and Principles:

• Newton’s Laws of Motion:

  • 1st (Inertia): Object at rest stays at rest; object in motion stays in motion unless acted upon by external force. Example: Passengers lurch backward when bus suddenly starts.
  • 2nd: F = ma (Force = mass × acceleration). Example: Pushing a loaded trolley vs empty trolley requires more force.
  • 3rd: Every action has equal and opposite reaction. Example: Walking — foot pushes backward on ground, ground pushes forward.

• Gravitation: Every object attracts every other object. F = Gm₁m₂/r². g = GM/r² = 9.8 m/s² on Earth’s surface.

  • Weight changes with location (less at equator and at altitude); mass remains constant.

• Work, Energy, Power:

  • Work = Force × Displacement × cos θ (Joules = NM)
  • Kinetic Energy = ½mv²; Potential Energy = mgh (gravitational)
  • Power = Work/Time = Energy/Time (Watts = Joules/second)

• Light:

  • Laws of reflection: Angle of incidence = Angle of reflection
  • Laws of refraction: Snell’s law — n₁ sin i = n₂ sin r (n = refractive index = c/v)
  • Total Internal Reflection: When angle of incidence in denser medium > critical angle → all light reflected. Used in optical fibres.
  • Lens formula: 1/v − 1/u = 1/f

• Electricity:

  • Ohm’s Law: V = IR
  • Series circuit: Same current, voltage divides
  • Parallel circuit: Same voltage, current divides
  • Power: P = VI = I²R = V²/R (Watts)
  • Household circuits: 3-pin plugs (earth wire saves from shock); fuse prevents overcurrent

⚡ Exam tip: For SSC CGL, remember that mass is constant everywhere but weight varies (zero in space, minimum at equator, maximum at poles). Also remember that 1 kWh = 3.6 million joules.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

General Science — SSC CGL Study Guide

Chemistry:

Periodic Table — Key Elements:

• Element with highest melting point: Tungsten (W, 3422°C) — used in light bulb filaments
• Lightest element: Hydrogen (H₂)
• Heaviest naturally occurring: Uranium (U, Z=92) or Osmium (Os, Z=76 — densest element, 22.59 g/cm³)
• Most abundant gas in Earth’s atmosphere: Nitrogen (N₂ = 78%), Oxygen (O₂ = 21%), Argon (Ar = 0.93%)

Chemical Bonds:

• Ionic bond: Transfer of electrons (metal + non-metal). Example: NaCl (sodium chloride — common salt). Properties: High melting point, soluble in water, conduct electricity in solution.
• Covalent bond: Sharing of electrons (non-metals). Example: Methane (CH₄), Water (H₂O), Diamond (C). Properties: Low melting point, generally insoluble in water.
• Hydrogen bond: Weak attraction between H and electronegative atoms (O, N, F). Example: Water molecules — gives water its high boiling point (100°C instead of −80°C).

Acids and Bases:

• Acid: H⁺ donor (Arrhenius); proton donor (Bronsted-Lowry); electron pair acceptor (Lewis)
• Base: OH⁻ donor (Arrhenius); proton acceptor (Bronsted-Lowry); electron pair donor (Lewis)
• pH scale: 0–14; pH < 7 is acidic; pH > 7 is basic; pH = 7 is neutral
• Strong acid: HCl, H₂SO₄, HNO₃ (fully dissociates)
• Weak acid: CH₃COOH (acetic acid/vinegar), H₂CO₃ (carbonic acid)
• Indicators: Methyl orange (acid = red, base = yellow); Phenolphthalein (acid = colourless, base = pink); Litmus (acid = red, base = blue)

Chemical Reactions:

• Oxidation: Loss of electrons; increase in oxidation state; gain of oxygen; loss of hydrogen
• Reduction: Gain of electrons; decrease in oxidation state; loss of oxygen; gain of hydrogen
• Redox: Both oxidation and reduction occur simultaneously
• Rusting of iron: 4Fe + 3O₂ + 2H₂O → 2Fe₂O₃·H₂O (rust — reddish brown flakes)
• Prevention: Painting, galvanisation (coating with zinc — zinc acts as sacrificial anode)

Biology:

Cell — Basic Unit of Life:

• All living organisms are composed of cells (Cell Theory: Schleiden + Schwann, 1838–39)
• All cells arise from pre-existing cells (Virchow, 1855)
• Prokaryotes: Bacteria, blue-green algae (no nuclear membrane)
• Eukaryotes: Plants, animals, fungi, protozoa (true nucleus)

Nutrition:

• Autotrophic: Make their own food (green plants — photosynthesis)
  • Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ (chlorophyll as catalyst)
• Heterotrophic: Cannot make their own food (animals, fungi, some plants like Venus flytrap)
• Holozoic: Ingest solid food (humans)
• Saprophytic: Feed on dead and decaying matter (fungi, some bacteria)

Respiration:

• Aerobic: Glucose + Oxygen → Carbon dioxide + Water + Energy (36 ATP) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
• Anaerobic (in yeast): Glucose → Ethanol + CO₂ + Energy (2 ATP) — bread making, brewing
• Anaerobic (in muscles during exercise): Glucose → Lactic acid + Energy (oxygen debt)

Human Digestive System:

Organ	Secretion	Function
Mouth	Saliva (amylase — Ptyalin)	Digests starch
Stomach	HCl + Pepsin	Digests proteins
Small intestine	Pancreatic juice (trypsin, lipase) + Bile (emulsifies fats) + Intestinal juice (maltase, lipase)	Complete digestion of all nutrients
Large intestine	No digestive enzymes	Water absorption, faeces formation

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

General Science — Comprehensive Notes

Physics — Additional Topics:

Magnetism:

• Magnetic field lines emerge from North pole, enter South pole
• Earth’s magnetic field: Geographic North = Magnetic South (thus compass needle points north)
• Oersted’s experiment: Electric current produces magnetic field (right-hand thumb rule)
• Fleming’s Left Hand Rule: Current → Magnetic field → Force (electric motor)
• Fleming’s Right Hand Rule: Motion → Magnetic field → Current (electric generator)
• Electromagnetic Induction (Faraday): Changing magnetic flux induces EMF/current (generators, transformers)

Sound:

• Speed of sound in air: 332 m/s at 0°C; increases ~0.6 m/s per °C
• In water: ~1,500 m/s; in steel: ~5,000 m/s
• Echo: Sound reflected back after minimum 17.2 m (for human ear to distinguish)
• SONAR: Uses ultrasound (>20 kHz) to detect underwater objects; echoes calculate distance
• Audible frequency range: 20 Hz to 20,000 Hz
• Infrasound: < 20 Hz (elephants, whales communicate); Ultrasound: > 20,000 Hz (bats, medical imaging)

Heat and Temperature:

Scale	Freezing Point	Boiling Point
Celsius (°C)	0°C	100°C
Fahrenheit (°F)	32°F	212°F
Kelvin (K)	273.15 K	373.15 K

Conversion: °C = (°F − 32) × 5/9; K = °C + 273.15

Latent Heat:

• Latent heat of fusion (ice): 336 J/g — energy needed to melt 1g of ice at 0°C without temperature change
• Latent heat of vaporisation (water): 2,260 J/g — energy needed to convert 1g water to steam at 100°C

Chemistry — Additional Topics:

Water (H₂O):

• Universal solvent (dissolves more substances than any other liquid due to polar nature)
• High specific heat capacity (4.18 J/g°C) — moderates Earth’s climate
• Maximum density at 4°C (expands on freezing — ice floats; this is anomalous)
• Hard water: Contains Ca²⁺ and Mg²⁺ ions; temporary hardness (bicarbonates) removed by boiling; permanent hardness (sulphates, chlorides) removed by washing soda or ion exchange

Metals and Non-Metals:

Property	Metals	Non-metals
Conductivity	Good (heat + electricity)	Poor
Malleability	Malleable	Brittle
Sonorous	Sonorous (ring when struck)	Not sonorous
State at room temp	Mostly solid (Hg = liquid)	Mostly gas (例外: Bromine = liquid, Iodine = solid)
Lustre	Metallic lustre	No lustre

Biology — Additional Topics:

Human Nervous System:

• CNS: Brain + Spinal cord
• Brain: Cerebrum (higher functions — thinking, memory, voluntary actions), Cerebellum (balance, coordination), Medulla oblongata (involuntary — heart rate, breathing)
• PNS: Somatic (voluntary) + Autonomic (involuntary — sympathetic + parasympathetic)
• Reflex arc: Receptor → Sensory neuron → Interneuron (in spinal cord) → Motor neuron → Effector (muscle/gland)

Human Endocrine System:

Gland	Hormone	Function
Pituitary (Master gland)	Growth hormone (GH), TSH, ACTH, FSH, LH, Prolactin, Oxytocin, ADH	Controls other glands; growth, reproduction, water balance
Thyroid	T3, T4 (Thyroxine), Calcitonin	Basal metabolic rate, development; Calcitonin lowers blood calcium
Parathyroid	PTH (Parathormone)	Raises blood calcium
Pancreas	Insulin (↓ blood sugar), Glucagon (↑ blood sugar)	Diabetes mellitus
Adrenal	Adrenaline (fight or flight), Cortisol (stress response)	Emergency response, metabolism
Ovary	Oestrogen, Progesterone	Female secondary sexual characteristics
Testis	Testosterone	Male secondary sexual characteristics

Diseases (Common):

• Diabetes Mellitus: Lack of insulin; sugar in urine; high blood glucose; Type 1 (autoimmune, children), Type 2 (lifestyle, adults)
• Hypertension: Blood pressure > 140/90 mmHg
• Anaemia: Low haemoglobin; iron deficiency most common
• Malaria: Caused by Plasmodium parasite (female Anopheles mosquito)
• Tuberculosis: Caused by Mycobacterium tuberculosis

NEET/SSC Pattern Analysis: General Science contributes 3–4 questions in SSC CGL Tier-I. Physics focuses on laws, formulas, and applications. Chemistry on periodic table, reactions, and daily-life applications. Biology on human body systems, nutrition, and diseases. Current science developments (ISRO missions, Nobel Prize in science, COVID-related biology) are increasingly asked.

⚡ SSC CGL 2022 Qn: Which gas is most abundant in the Earth’s atmosphere? Answer: Nitrogen (N₂ — 78%); Oxygen is second at 21%.