Physics — Last-Minute Revision
30 must-know Physics points covering all 14 chapters. Read through this the night before or morning of your TGBIE 1st Year Physics exam.
Significant figures: the number of reliable digits. For multiplication/division, use the number with fewest significant figures.
Dimensional analysis: [Force] = MLT⁻², [Energy] = ML²T⁻², [Pressure] = ML⁻¹T⁻².
Kinematic equations: v=u+at, s=ut+½at², v²=u²+2as. Valid only for uniform acceleration.
For vertical motion under gravity: take downward as positive. g = 9.8 m/s² (use 10 for quick calculations).
Projectile: Horizontal velocity stays constant (no air resistance). Vertical follows free fall.
Range R = u²sin2θ/g; max at 45°. R(30°) = R(60°) = R_max/√2 × √3 — same range for complementary angles.
Newton's 3rd law: action and reaction are equal, opposite, and act on DIFFERENT bodies.
Static friction: f ≤ μₛN. Kinetic friction: f = μₖN. μₖ < μₛ always.
Work done by friction is always negative (dissipates energy). Work by normal force = 0 (perpendicular to motion).
Work-Energy theorem: W_net = ΔKE. This applies even when forces are not constant.
Elastic collision: both KE and momentum conserved. Inelastic: only momentum conserved.
Power = Work/time = Force × velocity = τω (for rotation).
Torque τ = r × F = Iα. Angular momentum L = Iω. τ = dL/dt.
Moment of inertia: rod (centre) ML²/12; rod (end) ML²/3; disc MR²/2; solid sphere 2MR²/5.
Parallel axis: I = I_cm + Md². Perpendicular axis (laminar): I_z = I_x + I_y.
Rolling KE = ½mv²(1 + I/mR²). For disc: ¾mv². For solid sphere: 7/10 mv².
SHM: a = −ω²x; v = ω√(A²−x²); max velocity = ωA at x=0.
T = 2π√(L/g) — pendulum period doesn't depend on mass or amplitude (small angles only).
Kepler's 3rd law: T² ∝ r³. This applies to any two planets/satellites around the same body.
Escape velocity: v_e = √(2gR) = √2 × v_o. For Earth: ~11.2 km/s.
g decreases with height (above surface) and decreases with depth (below surface). g = 0 at Earth's centre.
Bernoulli: faster flow = lower pressure. Applications: airplane wings, Venturimeter, atomiser.
Surface tension: force per unit length (N/m). Excess pressure in soap bubble = 4T/r (two surfaces).
Thermal expansion: linear ΔL = αLΔT; area ΔA = 2αAΔT; volume ΔV = 3αVΔT.
1st law of thermodynamics: ΔU = Q − W. For isothermal: ΔU = 0 (ideal gas). For adiabatic: Q = 0.
Carnot efficiency: η = 1 − T₂/T₁. This is the maximum possible — no real engine reaches it.
2nd law: heat cannot spontaneously flow from cold to hot. This is why η < 100% always.
Ideal gas: PV = nRT. At STP: 1 mole of gas occupies 22.4 L.
v_rms = √(3kT/m) = √(3RT/M). At higher temperature, molecules move faster.
Equipartition: each degree of freedom has energy ½kT per molecule. Monoatomic: 3 DOF, Cv = 3/2 R.