Specialty Density Formulas

Formula: Population Density = Total Population ÷ Area

Units: people/km² or people/mi²

Application: Determines population concentration. Higher density = more crowded.

Example: NYC: ~11M people ÷ 783 km² = 14,050 people/km²

Formula: B = F / (q × v × sin θ)

Units: Tesla (T)

Application: Measures magnetic field strength in physics and electromagnetics

Formula: J = I / A

Where: J = current density, I = current, A = cross-sectional area

Units: Amperes/m² (A/m²)

Application: Current flow per unit area in electrical conductors

Formula: ρ = Q / V

Units: Coulombs/m³ (C/m³)

Application: Electric charge distribution in electromagnetism

Formula: OD = log₁₀(I₀ / I)

Application: Measures light absorption in spectroscopy and microbiology

Formula: u = E / V

Units: Joules/m³ (J/m³)

Application: Energy stored per volume (batteries, fuel, radiation)

Formula: Relative Density = ρ_substance / ρ_water

Units: Dimensionless

Application: Compares any substance's density to water (reference = 1.0)

Example: Gold = 19.3 g/cm³ ÷ 1.0 g/cm³ = 19.3

Bulk Density: ρ_b = m / V_total

Includes all voids and pores (for granular materials)

Particle Density: ρ_p = m / V_solid

Only solid material (excluding pores). Always ≥ bulk density.

• "Density" means different things in different fields
• All use the principle: quantity per unit (volume, area, or range)
• Context determines which density formula to use
• Each field has specialized units and applications
• Relative density simplifies cross-field comparisons