Browse All 842 Physics Terms A–Z

Pitch Waves, Oscillations & Acoustics Hz (or Musical Notes) The subjective psychoacoustic perception of a sound's frequency by human listeners. Pitch ∝ f

Planck's Constant Foundations of Physics J·s A fundamental physical constant that sets the scale for quantum mechanical phenomena, relating photon energy to its frequency. E = hf, h = 6.62607015 × 10⁻³⁴ J·s

Planck's Law & Blackbody Radiation Quantum & Atomic Physics W / (m²·sr·Hz) The foundational law describing the spectral radiance of electromagnetic radiation emitted by a blackbody in thermal equilibrium. B_ν(T) = (2 h ν³ / c²) / (e^(h ν / (k_B T)) - 1), E = h ν

Plasma Antenna Plasma Physics MHz / GHz (RF Operating Frequency) A radiofrequency antenna that uses ionized plasma gas instead of solid metal conductors to transmit and receive electromagnetic signals. Conductivity σ_p = (n_e e²) / (m_e (ν_coll - i ω))

Plasma Astrophysics Plasma Physics Cosmic Plasma Physics The branch of astrophysics applying plasma physics and magnetohydrodynamics to model cosmic phenomena throughout the universe. B² / (2 μ₀) ~ ρ v² ~ P_thermal (Cosmic Equipartition)

Plasma Beta Plasma Physics Dimensionless Ratio The ratio of kinetic thermal plasma pressure to magnetic field pressure in a magnetized plasma. β = p_kinetic / p_magnetic = (n k_B T) / (B² / (2 μ₀))

Plasma Etching Plasma Physics nm/min (Etch Rate) & Aspect Ratio A semiconductor manufacturing process using reactive gas plasmas to selectively remove surface layers from microchip wafers. Anisotropic Reactive Ion Etching (RIE)

Plasma Frequency Plasma Physics rad/s (Angular Frequency) The natural characteristic frequency of collective electrostatic electron oscillations in a plasma when perturbed from thermal equilibrium. ω_pe = √(n_e e² / (m_e ε₀))

Plasma Medicine Plasma Physics Biomedical Application An emerging field of medical physics applying non-thermal atmospheric pressure plasmas directly to living tissues for therapeutic treatment. RONS Generation: NO, O₂⁻, H₂O₂, OH•, ONOO⁻

Plasma Parameter Plasma Physics Dimensionless Number of Particles in Debye Sphere A fundamental dimensionless number in plasma physics measuring the average number of electrons contained within a Debye sphere. Λ = n_e λ_D³ ≫ 1

Plasma Sheath Plasma Physics V (Sheath Voltage) & m (Thickness ~ λ_D) A thin non-neutral positive boundary layer formed in a plasma adjacent to any physical wall or electrode. V_sheath ≈ (k_B T_e / (2 e)) ln(m_i / (2 π m_e)), v_ion ≥ c_s = √(k_B T_e / m_i)

Plasma Torch Plasma Physics kW to MW (Electrical Power Input) An electromechanical device that generates a high-temperature thermal plasma jet by passing inert or reactive gas through an electric arc discharge. Thermal Equilibrium T_gas ≈ T_electron ~ 5,000–15,000 K

Plasma Wave Dispersion Relations Plasma Physics ω vs k (Dispersion Relation Curve) Mathematical equations relating wave frequency ω to wavevector k for electromagnetic and electrostatic waves propagating through magnetized plasmas. CMA Diagram (Clemmow-Mullaly-Allis Wave Mode Classification)

Plate Tectonics Geophysics & Environmental Physics cm/year (Plate Drift Speed) The unifying geophysical theory stating that Earth's rigid outer lithosphere is divided into major tectonic plates drifting over the ductile asthenosphere. Plate Motion Velocity v_plate ~ 1–10 cm/year

Poiseuille's Law of Blood Flow Biophysics & Medical Physics m³/s or L/min (Volumetric Flow Rate) A fluid dynamics equation governing laminar viscous fluid flow through a cylindrical vascular pipe. Q = (π r⁴ ΔP) / (8 η L)

Poisson Brackets Mathematical & Computational Physics Phase Space Operation An algebraic operation between two phase space functions describing time evolution and conservation laws in Hamiltonian mechanics. {f, g} = ∑ ((∂f / ∂q_i)(∂g / ∂p_i) - (∂f / ∂p_i)(∂g / ∂q_i))

Poisson's Ratio Condensed Matter & Materials Physics Dimensionless Ratio (-1 to 0.5) The ratio of transverse lateral strain to axial longitudinal strain in a material subjected to uniaxial stress. ν = -ε_transverse / ε_axial = -(Δd / d₀) / (ΔL / L₀)

Polar Coordinates Foundations of Physics m, rad A 2D coordinate system specifying point location by radial distance r from the origin and angular displacement θ from a reference axis. x = r cos θ, y = r sin θ, r = √(x² + y²)

Polarization Optics N/A The property of transverse electromagnetic waves specifying the geometric orientation of their electric field vector oscillations in space. E(z,t) = E0 cos(k z - ω t) i_hat

Polaron Condensed Matter & Materials Physics Quasiparticle Mass A composite quasiparticle consisting of a conduction electron (or hole) bound together with its surrounding self-induced lattice polarization distortion cloud in an ionic crystal. m*_polaron = m* (1 + α_coupling / 6)

Population Inversion Quantum & Atomic Physics Dimensionless Condition A non-equilibrium state of a quantum system where more atoms reside in a higher excited energy state than in lower energy states. N₂ > N₁ (Excited state density > Ground state density)

Positron Emission Tomography (PET Scan) Biophysics & Medical Physics MBq (Activity) & Standardized Uptake Value (SUV) A 3D nuclear medicine imaging technique detecting pairs of 511 keV gamma photons emitted during positron annihilation to map metabolic activity. Coincidence Detection of 180° Back-to-Back 511 keV Gamma Photons

Potential Energy Classical Mechanics J The stored energy an object possesses due to its relative position in a conservative force field or its structural deformation. PE_grav = m g h, PE_elastic = ½ k x²

Power Classical Mechanics W (J/s) The rate at which work is performed or energy is transferred per unit time. P = dW/dt = F · v

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