General Science: Physics — SSC CGL General Awareness
SSC physics never asks you to solve; it asks you to recognise. Which unit, which law, which lens, which effect — every question maps a daily-life phenomenon to its textbook principle. The menu below has fed the exam for a decade; read it as a phenomenon-to-principle dictionary.
1. What SSC actually asks
Tier 1: 2–3 Q · Tier 2: 2–3 Q inside the General Awareness section's science block (science overall: 7–10 Q across physics, chemistry, biology). Recurring stems: SI unit of X, which law explains Y, which lens/mirror for Z, sound travels fastest in…, a fuse works on….
2. Units and measurement — the free marks
| Quantity | SI unit | Watch out |
|---|---|---|
| Force | newton (N) | — |
| Work / energy | joule (J) | kWh is energy, not power |
| Power | watt (W) | horsepower ≈ 746 W |
| Pressure | pascal (Pa) | atmosphere, bar, torr = non-SI |
| Frequency | hertz (Hz) | — |
| Electric charge | coulomb (C) | current = ampere (base unit) |
| Resistance | ohm (Ω) | conductance = siemens |
| Temperature | kelvin (K) | 0 °C = 273 K; °F = °C × 9/5 + 32 |
Scalar vs vector is a repeat question: speed, distance, energy, temperature are scalars; velocity, displacement, force, momentum are vectors.
3. Mechanics — laws in daily life
- Newton I (inertia): passengers jerk forward when a bus brakes; dust leaves a beaten carpet.
- Newton II: — a cricketer draws hands back while catching (increases time, cuts force).
- Newton III: rockets, gun recoil, swimming — action–reaction. (Rocket propulsion = third law + conservation of momentum; it does NOT need air to push against.)
- Work ; no displacement → no work (holding a suitcase stationary does zero work).
- Gravitation: , decreases with altitude and depth, maximum at the poles. Escape velocity of Earth = 11.2 km/s. Weightlessness in orbit = continuous free fall, not "no gravity".
4. Light — lenses, defects, phenomena
- Speed in vacuum: m/s — nothing travels faster; light needs no medium.
- Reflection → mirrors, periscope; refraction → a coin in water looks raised, stars twinkle, a pencil looks bent in water.
- Scattering (Rayleigh): sky is blue, danger signals are red (red scatters least, travels farthest).
- Dispersion: prism splits white light; rainbow = dispersion + internal reflection in raindrops.
- Eye defects: myopia (near-sight) → concave lens; hypermetropia (far-sight) → convex lens; astigmatism → cylindrical lens.
- Mirrors: rear-view = convex (wide field, diminished image); shaving/dentist = concave (magnified when close).
5. Sound
- Longitudinal mechanical wave — cannot travel in vacuum (a bell in an evacuated jar goes silent).
- Speed order: solids > liquids > gases (~5000 m/s in steel, ~1500 in water, ~340 in air).
- Audible range 20 Hz – 20 kHz; below = infrasonic (earthquakes), above = ultrasonic (bats, SONAR, medical ultrasound).
- Echo = reflection of sound; minimum distance to hear one ≈ 17 m (round trip in 0.1 s).
- Pitch ↔ frequency; loudness ↔ amplitude; SONAR uses ultrasonic reflection underwater.
6. Heat and thermodynamics
- Conduction (solids, metals — handle of a pan), convection (liquids/gases — sea breeze), radiation needs no medium (sun's heat).
- Water's peculiar expansion: densest at 4 °C — lakes freeze from the top, fish survive below.
- Cooking is faster in a pressure cooker: higher pressure raises the boiling point.
- Black surfaces absorb and emit best; white/shiny reflect — why summer clothes are light-coloured.
- Thermos flask blocks all three transfer modes (vacuum + silvered walls).
7. Electricity and magnetism
- Ohm's law: . Household wiring is parallel (same voltage, independent appliances).
- Fuse / electric iron / heater / bulb filament work on the heating effect of current; the fuse wire has low melting point (filament: tungsten, high melting point).
- Electric motor: electrical → mechanical. Generator/dynamo: mechanical → electrical (electromagnetic induction — Faraday). Transformer: changes AC voltage; works only on AC.
- Earth wire = safety route for leakage current; MCBs replace fuses in modern homes.
- A freely suspended magnet rests north–south; like poles repel — repulsion is the sure test of a magnet.
8. Solved PYQ-style examples
Q1. Sound travels fastest in: vacuum / air / water / steel. Solution. Solids fastest; vacuum carries no sound at all. Steel.
Q2. Myopia is corrected using a: Solution. Near-sighted eye focuses in front of the retina → diverge the rays → concave lens.
Q3. An electric fuse works on the ______ of current. Solution. Heating effect — the low-melting wire melts on overload and breaks the circuit.
Q4. kWh is the unit of: Solution. Power × time = energy (1 kWh = 3.6 × 10⁶ J — the electricity-bill "unit").
Q5. A rocket works on the principle of: Solution. Conservation of momentum / Newton's third law — exhaust down, rocket up; no air needed.
9. Exam protocol
- Unit questions are 10-second marks — bank them first; watch the kWh-is-energy trap.
- Phenomenon questions: name the principle, not the story (sky blue → scattering; twinkle → refraction; echo → reflection).
- Lens questions: myopia–concave, hypermetropia–convex — say it as one memorised couplet.
- "Fastest/slowest" orderings (sound in media, g at poles vs equator) are fixed facts — no reasoning needed at the desk.
- Science block questions take 15–20 seconds each; know-or-skip, and spend the savings on quant.
