Physics Questions for SSC CGL

Mechanics — Motion, Force, Work

Mechanics forms the backbone of SSC physics. You need to know Newton's three laws, the difference between speed and velocity, and how to apply work-energy concepts. Most questions test conceptual understanding rather than complex math. For example, 'Why does a moving bus passenger lurch forward when brakes are applied?' tests Newton's first law. Questions often link to real-world scenarios like friction, circular motion, or simple machines.

• Newton's First Law: object at rest stays at rest unless external force acts (inertia)
• Newton's Second Law: F = ma; force causes acceleration proportional to mass
• Newton's Third Law: action-reaction pairs are equal and opposite
• Work = Force × Displacement × cos(angle); measured in Joules
• Kinetic Energy = 0.5 × m × v²; increases with speed squared
• Potential Energy = mgh; depends on height and gravitational field

Heat and Thermodynamics

Heat questions in SSC CGL focus on temperature scales, specific heat, latent heat, and thermal expansion. You rarely need to solve complex thermodynamic equations. Instead, know the difference between heat and temperature, understand phase changes, and recognize that heat always flows from hot to cold. Questions often ask about everyday phenomena like why metals expand in summer or how a thermometer works.

• Temperature: measure of average kinetic energy of particles; units Celsius, Kelvin, Fahrenheit
• Heat: energy transfer due to temperature difference; measured in Joules or calories
• Specific Heat: energy needed to raise 1 kg by 1°C; water has high specific heat (4200 J/kg°C)
• Latent Heat: energy for phase change (solid-liquid-gas) without temperature change
• Thermal Expansion: solids expand when heated; coefficient α varies by material
• Conduction, Convection, Radiation: three modes of heat transfer

Light and Optics

Light questions test understanding of reflection, refraction, lenses, and mirrors. SSC CGL rarely asks for ray diagram construction but frequently tests conceptual knowledge. Know the laws of reflection and refraction, focal length, and how convex/concave lenses behave. Questions often relate to everyday objects like mirrors, spectacles, or cameras.

• Law of Reflection: angle of incidence = angle of reflection; both measured from normal
• Refraction: light bends when entering denser medium; follows Snell's Law
• Refractive Index: n = c/v; higher n means slower light, more bending
• Convex Lens: converges light, forms real/virtual images depending on object distance
• Concave Lens: diverges light, always forms virtual, erect, diminished image
• Focal Length: distance from lens/mirror where parallel rays converge; f = R/2 for spherical mirrors

Electricity and Magnetism

Electricity is a high-frequency topic in SSC CGL. Focus on Ohm's Law, circuit basics, and power calculations. Magnetism questions are lighter but test understanding of magnetic field, poles, and electromagnetic induction. Know the difference between series and parallel circuits, how resistance adds, and practical applications like fuses and earthing.

• Electric Current: flow of charge; measured in Amperes (A); I = Q/t
• Voltage (Potential Difference): energy per unit charge; measured in Volts (V)
• Resistance: opposition to current flow; measured in Ohms (Ω); R = ρL/A
• Ohm's Law: V = IR; voltage = current × resistance
• Power: P = VI = I²R = V²/R; measured in Watts (W)
• Series Circuit: same current, voltages add, resistances add; Parallel: same voltage, currents add, 1/R_total = 1/R₁ + 1/R₂...

Modern Physics — Atoms and Radioactivity

Modern physics in SSC CGL is conceptual. You need to know basic atomic structure, the nucleus, radioactivity types, and half-life. Questions test understanding rather than calculation. Know that alpha decay reduces mass number, beta decay changes atomic number, and gamma is pure energy. Practical applications like carbon dating or nuclear power are common themes.

• Atom: nucleus (protons + neutrons) surrounded by electrons in orbitals
• Atomic Number Z: number of protons; defines element
• Mass Number A: protons + neutrons; A = Z + N
• Isotopes: same Z, different N; different mass, similar chemistry
• Radioactivity: spontaneous nuclear decay; alpha (He nucleus), beta (electron), gamma (photon)
• Half-life: time for half of radioactive sample to decay; exponential decay N = N₀ × (1/2)^(t/t_half)

• Confusing speed and velocity: speed is scalar (magnitude only), velocity is vector (magnitude + direction). SSC asks 'which is a vector?' — answer is velocity.
• Mixing up heat and temperature: heat is energy transfer, temperature is a property. A large cold object has more heat energy than a small hot object if its mass is much larger.
• Forgetting angle in work formula: Work = F × d × cos(θ). If force is perpendicular to displacement, work is zero, not F × d.
• Series vs parallel resistance errors: In series, R_total = R₁ + R₂. In parallel, 1/R_total = 1/R₁ + 1/R₂. Many aspirants reverse these.
• Misremembering lens behavior: Convex lens converges (like a magnifying glass), concave diverges. Convex mirrors diverge (wider field of view in car mirrors).
• Ignoring sign conventions in optics: Real images are positive distance, virtual are negative. This affects lens formula results.

• Newton's Laws mnemonic: 'Inertia, Force, Action' — First law (inertia), Second law (F=ma), Third law (action-reaction).
• Heat Transfer modes: 'CoCo-Ra' — Conduction (direct contact), Convection (fluid movement), Radiation (electromagnetic waves).
• Lens types: 'Convex Converges, Concave Curves away' — Convex is fat in middle (converges light), concave is thin in middle (diverges).
• Circuit series-parallel: 'Series = Single path (resistances add like people in a queue)', 'Parallel = Multiple paths (current splits like traffic lanes)'.
• Radioactive decay: 'Alpha loses mass (He nucleus), Beta changes type (electron), Gamma is just energy (photon)' — remember A decreases in alpha, Z changes in beta.

• SSC CGL physics is 80% conceptual, 20% calculation. Spend time understanding 'why' rather than memorizing formulas. Recent papers ask 'which statement is true?' not 'calculate the value.'
• Time pressure is real: you get ~1.5 minutes per question. Pre-memorize key values like specific heat of water (4200 J/kg°C), g = 10 m/s², speed of light = 3 × 10⁸ m/s.
• Everyday application questions are common: 'Why do we use copper wires?' (low resistance), 'Why do we earth appliances?' (safety), 'Why does ice float?' (density). Link concepts to real life.
• Diagram-based questions appear frequently but are not complex. You don't need to draw; just identify the concept (reflection, refraction, circuit type) and apply the rule.
• Watch for unit traps: a question might give energy in calories but ask for Joules, or temperature in Celsius when you need Kelvin. Always convert first.