Common Errors, Misconceptions, and NEET Traps

Bubble vs drop excess pressure (most common trap): $\Delta P$ = 4S/R for a soap bubble (two surfaces); $\Delta P$ = 2S/R for a liquid drop (one surface). Never use 2S/R for a bubble.
Terminal velocity proportionality: v_t ∝ $r^{2}$ (not r). Doubling radius quadruples terminal velocity. Answer choices 1:4 (not 1:2) for radius ratio 1:2.
Strain units: Strain is dimensionless ( $\Delta L$ /L). It has no unit. Only stress has unit Pa.
Stress-strain curve points: Proportional limit ≠ Elastic limit. Proportional limit comes first; elastic limit comes second on the curve.
Bernoulli's applicability: Only valid for ideal (non-viscous, incompressible), steady, streamline flow. Cannot apply to turbulent or viscous flows.
Capillary depression: Mercury in glass shows depression (θ > 90°, cosθ < 0, h < 0). Do not assume all liquids rise in capillary tubes.
β ≠ 2α: Volume expansion β = 3α; Area expansion = 2α. The factor 2 applies to area, not volume.
Temperature in Kelvin: Stefan-Boltzmann law P = σ $AT^{4}$ requires T in Kelvin. Converting from Celsius to Kelvin is mandatory.
All moduli have same dimensions: Y, B, G all have [ $M^{1}$ $L^{-1}$ $T^{-2}$ ] (Pa). Students sometimes think different moduli have different dimensional formulas.
Pascal's law — pressure vs force: Pascal's law states pressure (not force) is equal throughout. Force scales with area: F = P × A.
$mm^{2}$ to $m^{2}$ conversion: NEET numerical traps often give area in $mm^{2}$ — must convert: 1 $mm^{2}$ = $1 \times 10^{-6}$ $m^{2}$ .