Science - Physics Questions for SSC CGL

Force, Motion & Newton's Laws

Newton's three laws form the backbone of mechanics questions in SSC CGL. First law (inertia) explains why you lurch forward when a bus stops. Second law links force to acceleration — the heavier the object or faster you want it to move, the more force needed. Third law (action-reaction) is tested via everyday examples: when you jump, you push Earth down, Earth pushes you up equally. SSC loves asking which law applies to a given scenario, or calculating force/acceleration using F=ma.

• First Law: Object at rest stays at rest unless external force acts (inertia)
• Second Law: F = ma; force causes acceleration proportional to mass
• Third Law: Every action has equal and opposite reaction
• Weight = mg (mass × gravity); varies with location, mass does not
• Normal force, friction, tension are contact forces; gravity is non-contact
• Common trap: confusing mass (kg) with weight (N or kgf)

Work, Energy & Power

Work is done when force moves an object in the direction of force. Energy is capacity to do work. SSC tests whether you know work is zero if force is perpendicular to motion, and that energy is conserved (never created/destroyed, only converted). Power is how fast work is done. These concepts appear in real-world scenarios: lifting weights, friction losses, efficiency of machines.

• Work = Force × Distance × cos(angle); if angle=90°, work=0
• Kinetic Energy = (1/2)mv²; depends on speed squared, so doubling speed quadruples KE
• Potential Energy = mgh; stored energy due to height or position
• Power = Work/Time; measured in Watts (1 W = 1 J/s)
• Energy conservation: Total mechanical energy (KE+PE) remains constant if no friction
• Efficiency = (Useful output / Total input) × 100%; always <100% due to friction/heat loss

Heat & Thermodynamics

Heat is energy transfer due to temperature difference. Temperature measures average kinetic energy of particles. SSC asks about specific heat (how much energy to raise 1 kg by 1°C), latent heat (energy to change state without temperature change), and the first law of thermodynamics (energy cannot be created/destroyed). Expect questions on thermal expansion, conduction/convection/radiation, and why ice melts or water boils.

• Heat flows from hot to cold; temperature is measure of hotness, not amount of heat
• Specific Heat Capacity (c): energy needed to raise 1 kg by 1°C; water has high c (4200 J/kg°C)
• Latent Heat: energy for phase change (solid→liquid or liquid→gas) without temperature change
• Conduction: heat transfer through direct contact (metal spoon in hot water)
• Convection: heat transfer via fluid movement (warm air rises, cold sinks)
• Radiation: heat transfer via electromagnetic waves (no medium needed, like sunlight)

Light & Sound

Light is electromagnetic radiation (travels in straight lines, speed ~3×10⁸ m/s in vacuum). Sound is mechanical wave (needs medium, speed ~340 m/s in air). SSC tests reflection (angle of incidence = angle of reflection), refraction (bending when light enters denser medium), and Doppler effect (frequency changes when source moves). Expect definitions of focal length, lens power, and why objects appear closer in water.

• Light travels in straight lines (rectilinear propagation); faster in vacuum than in medium
• Reflection: angle of incidence = angle of reflection; mirror law
• Refraction: light bends when entering denser medium (e.g., air to water); Snell's Law applies
• Convex lens converges light (magnifying glass); concave lens diverges light
• Focal length (f): distance from lens where parallel rays meet; Power = 1/f (in diopters if f in meters)
• Sound: longitudinal wave; Doppler effect causes frequency change when source/observer moves

Electricity & Magnetism

Electricity involves charge, current (flow of charge), voltage (potential difference), and resistance. Ohm's Law (V=IR) is tested frequently. SSC asks about series vs. parallel circuits, power consumption, and basic electromagnetic concepts. Magnetism covers magnetic field, poles, and Earth's magnetic field. Expect simple circuit problems and why electromagnets work.

• Electric Current (I): flow of charge; measured in Amperes (A); I = Q/t
• Voltage (V): potential difference; energy per unit charge; measured in Volts
• Resistance (R): opposition to current; measured in Ohms (Ω); R = ρL/A (ρ=resistivity, L=length, A=area)
• Ohm's Law: V = IR; current proportional to voltage, inversely proportional to resistance
• Series circuit: same current, voltages add; Parallel circuit: same voltage, currents add
• Power = VI = I²R = V²/R; measured in Watts; Energy = Power × Time

Modern Physics Basics

SSC includes light topics from modern physics: atoms, nuclei, radioactivity, and basic quantum ideas. You need to know that atoms have nucleus (protons+neutrons) and electrons orbiting. Radioactivity is spontaneous decay of unstable nuclei. Half-life is time for half the sample to decay. These appear as definition questions or simple numerical problems.

• Atom: nucleus (protons + neutrons) surrounded by electrons; nucleus is tiny but contains most mass
• Atomic Number (Z): number of protons; Mass Number (A): protons + neutrons
• Radioactivity: spontaneous decay of unstable nuclei; alpha (He nucleus), beta (electron), gamma (radiation) decay
• Half-life: time for half the radioactive sample to decay; exponential decay follows N = N₀(1/2)^(t/T)
• E=mc²: mass-energy equivalence; small mass converts to huge energy
• Isotopes: same element (same Z), different mass number (different neutrons)

• Confusing mass (kg) with weight (N). Weight changes with gravity; mass does not. On Moon, you weigh less but have same mass.
• Thinking work is done whenever force is applied. Work = 0 if force is perpendicular to motion. Carrying a box horizontally does zero work against gravity.
• Forgetting that kinetic energy depends on speed squared. Doubling speed quadruples KE, not doubles it.
• Mixing up heat and temperature. Heat is energy transfer; temperature is measure of hotness. A large cold object can have more heat energy than a small hot object.
• In circuits, assuming series and parallel behave the same. Series: same current, voltages add. Parallel: same voltage, currents add. Resistance in series adds; in parallel, reciprocals add.
• Misapplying lens formula signs. Convex lens has positive f; concave has negative f. Real images (inverted) have positive v; virtual images (upright) have negative v.

• Newton's Laws: INF = Inertia, Newton's 2nd (F=ma), Force pairs (action-reaction)
• Energy types: KE (moving), PE (height), Heat (temperature difference). Total mechanical energy conserved if no friction.
• Heat transfer: Conduction (Contact), Convection (Current/fluid), Radiation (no medium needed). Remember CCC.
• Lens: Convex = Converging = Positive focal length; Concave = Diverging = Negative focal length. Think 'Convex Converges'.
• Ohm's Law: V=IR. Higher voltage → higher current. Higher resistance → lower current. Think 'Voltage drives, Resistance opposes'.
• Radioactive decay: Half-life halves the sample each period. After 3 half-lives, 1/8 remains (1/2 × 1/2 × 1/2).

• SSC CGL Tier-1 typically has 3-5 physics questions in 60 GK questions. Each question has 4 options and 2-minute time limit for all GK. Spend <1 minute per physics question — they are usually straightforward definitions or single-step calculations.
• High-frequency topics: Newton's laws (especially action-reaction), work-energy, specific heat, Ohm's Law, and lens formula. These appear in 70% of papers. Master these first.
• Numerical problems are simple (no complex algebra). Example: 'A 2 kg object accelerates at 5 m/s². Force applied?' Answer in 10 seconds using F=ma. Avoid overthinking.
• Conceptual questions often ask 'why' or 'which law applies'. Example: 'Why does a person lurch forward when a bus stops suddenly?' Answer: Newton's First Law (inertia). No calculation needed.
• Recent papers (2022-2024) show increased focus on real-world applications: thermal expansion in bridges, Doppler effect in ambulance sirens, efficiency of machines. Read the scenario carefully before jumping to formulas.
• Avoid trap options that confuse related concepts: mass vs. weight, heat vs. temperature, reflection vs. refraction. Read all 4 options; often one is a common mistake.