General Science — Study Notes for SSC CHSL

Overview

General Science contributes approximately 15–20 questions out of 100 in SSC CHSL Tier 1, making it a crucial scoring area. This section tests basic concepts from high school Physics, Chemistry and Biology—not advanced theory. Questions are typically factual ("What is the SI unit of force?") or application-based ("Which vitamin deficiency causes scurvy?").

Success requires memorizing fundamental definitions, units, processes and organ functions rather than deriving complex equations. The exam focuses on everyday science: how things work, what causes what, and standard classifications. Most questions can be answered in 10–15 seconds if you have the factual base locked in. Candidates who neglect this section lose easy marks, while those who systematically cover all three branches gain a decisive edge.

Your strategy: build a strong foundation in Physics laws and units, Chemistry's periodic trends and reactions, and Biology's human body systems. Prioritize high-frequency topics like vitamins, diseases, simple machines, acids-bases, and cell structure. Revise using flashcards for quick recall on exam day.

Key Concepts

• **Physics is measurement and motion**: Force, energy, work, power and their SI units form the backbone. Newton's laws govern motion; simple machines multiply force or speed.
• **Electricity basics matter**: Current (ampere), voltage (volt), resistance (ohm) and Ohm's law (V = IR) appear frequently. Know series vs parallel circuits and how household electricity works.
• **Light and optics**: Reflection, refraction, mirrors (concave/convex), lenses and the human eye. Remember: convex lens converges light, concave diverges.
• **Chemistry revolves around elements and reactions**: The periodic table organizes elements by atomic number. Metals, non-metals and metalloids have distinct properties.
• **Acids, bases and salts are exam favorites**: pH scale (0–14), common acids (HCl, H₂SO₄), bases (NaOH, Ca(OH)₂) and neutralization reactions yield salt + water.
• **Biology emphasizes the human body**: Know the function of major organs (heart pumps blood, lungs exchange gases, kidneys filter waste) and systems (circulatory, respiratory, digestive, nervous).
• **Vitamins and diseases link directly**: Vitamin A (vision), B-complex (energy), C (scurvy), D (rickets), E (antioxidant), K (clotting). Deficiency diseases appear in 2–3 questions every year.
• **Cell is the basic unit of life**: Prokaryotic (no nucleus, bacteria) vs eukaryotic (nucleus present, animals/plants). Organelles: mitochondria (powerhouse), ribosomes (protein synthesis), chloroplasts (photosynthesis in plants).

Formulas / Key Facts

**Physics**

• Speed = Distance / Time; SI unit: m/s
• Force = Mass × Acceleration; SI unit: newton (N)
• Work = Force × Displacement; SI unit: joule (J)
• Power = Work / Time; SI unit: watt (W)
• Kinetic Energy = ½ mv²; Potential Energy = mgh
• Ohm's Law: V = IR (Voltage = Current × Resistance)
• Density = Mass / Volume; SI unit: kg/m³

**Chemistry**

• Atomic number = Number of protons in nucleus
• pH < 7 = Acidic; pH = 7 = Neutral; pH > 7 = Basic
• Valency: Hydrogen = 1, Oxygen = 2, Nitrogen = 3, Carbon = 4
• Rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ (oxidation reaction)
• Common salt: NaCl; Baking soda: NaHCO₃; Washing soda: Na₂CO₃·10H₂O
• Noble gases (Group 18): Helium, Neon, Argon, Krypton, Xenon, Radon (inert)

**Biology**

• Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ (occurs in chloroplasts)
• Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (occurs in mitochondria)
• Human heart: 4 chambers (2 atria, 2 ventricles); normal rate 72 beats/min
• Blood groups: A, B, AB, O; universal donor = O, universal recipient = AB
• DNA structure: Double helix discovered by Watson and Crick
• Normal human body temperature: 37°C or 98.6°F

Worked Examples

**Example 1: A car travels 180 km in 3 hours. What is its average speed?** Step 1: Use formula Speed = Distance / Time Step 2: Speed = 180 km / 3 hours = 60 km/h Answer: 60 km/h

**Example 2: If a 5 V battery is connected to a 10 Ω resistor, what current flows?** Step 1: Apply Ohm's law V = IR → I = V/R Step 2: I = 5 V / 10 Ω = 0.5 A Answer: 0.5 ampere

**Example 3: Which vitamin deficiency causes night blindness?** Step 1: Recall vitamin functions—Vitamin A maintains vision and healthy skin Step 2: Deficiency of Vitamin A leads to night blindness (nyctalopia) Answer: Vitamin A

**Example 4: What is the pH of lemon juice (acidic)?** Step 1: Acidic substances have pH < 7 Step 2: Lemon juice contains citric acid; typical pH ≈ 2–3 Answer: Around 2–3 (acidic)

Common Mistakes

• **Confusing speed and velocity**: Speed is scalar (magnitude only), velocity is vector (magnitude + direction). Exam asks for "speed" in most cases—just use distance/time.
• **Mixing up concave and convex**: Concave mirror/lens curves inward (caves in), convex bulges outward. Concave mirror can form real or virtual images depending on object position; convex mirror always forms virtual, diminished images.
• **Believing all metals conduct equally**: While most metals conduct, conductivity varies. Silver conducts best, then copper, then aluminum. Non-metals like graphite (carbon form) also conduct—exception to the rule.
• **Forgetting pH is logarithmic**: pH 6 is 10× more acidic than pH 7, not just "1 unit more." Each pH unit represents a tenfold change in hydrogen ion concentration.
• **Thinking vitamins are produced in the body**: Most vitamins must come from food. Exception: Vitamin D (synthesized when skin is exposed to sunlight) and Vitamin K (produced by gut bacteria).

Quick Reference

• **SI unit trio**: Force (newton), Energy (joule), Power (watt)
• **Ohm's law shortcut**: V = IR (Voltage equals Current times Resistance)
• **pH memory**: 0–6 acidic, 7 neutral, 8–14 basic
• **Vitamin A → Eyes, C → Scurvy, D → Bones (rickets), K → Blood clotting**
• **Mitochondria = Cell's powerhouse; Nucleus = Control center; Ribosomes = Protein factories**
• **Photosynthesis in chloroplasts (plants); Respiration in mitochondria (all cells)**
• **Universal blood donor = O; Universal recipient = AB**
• **Noble gases = Chemically inert (Group 18 elements)**

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**Pro tip**: Make a one-page chart of vitamins-deficiency-sources, another for SI units, and a third for common chemical formulas. Revise these daily in the final week. General Science rewards consistent factual recall—no shortcuts, just disciplined memorization and practice.