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Condensed Matter & Materials Physics

N-type Semiconductor

An extrinsic semiconductor in which pentavalent donor impurities create an excess concentration of free electrons as majority charge…

n ≈ N_D ≫ p, n p = n_i² cm⁻³ (Electron Concentration) Biophysics & Medical Physics

Nanomedicine

The medical application of nanotechnology utilizing engineered nanoparticles for disease diagnosis, targeted drug delivery, and therapy.

EPR Effect: Enhanced Permeability and Retention in Tumors nm (Nanoparticle Diameter ~10–100 nm) Optics

Near Point & Far Point

The closest and farthest distances at which the human eye can focus objects sharply on the retina.

Near Point ≈ 25 cm (Normal adult eye), Far Point = ∞ m (or cm) Astrophysics, Cosmology & Relativity

Nebula

An interstellar cloud of dust, hydrogen, helium, and ionized gases in space, serving as a site for star formation.

M_Jeans = (5 k_B T / (G μ m_H))^(3/2) (3 / (4 π ρ))^(1/2) Light-Years (Diameter) Biophysics & Medical Physics

Nernst Equation in Biophysics

An equation calculating the exact electrical equilibrium potential across a membrane permeable to a single ion species.

E_ion = (R T / (z F)) ln([Ion]_out / [Ion]_in) mV (Equilibrium Potential) Biophysics & Medical Physics

Neurophysics

The interdisciplinary field applying physical principles and non-linear mathematical modeling to study nervous system function.

Hodgkin-Huxley Model: C_m (dV/dt) = I_ext - g_Na m³ h (V-E_Na) - g_K n⁴ (V-E_K) - g_L (V-E_L) Biophysical Neural Network Model Plasma Physics

Neutral Beam Injection (NBI)

A primary plasma heating and current drive method where high-energy neutral atom beams are injected into a magnetic confinement fusion…

P_NBI = I_beam × V_acceleration MW (Beam Power) & keV (Particle Energy ~100–1000 keV) Nuclear & Particle Physics

Neutrino

An extremely light, electrically neutral spin-1/2 elementary lepton that interacts almost exclusively via the weak nuclear force.

m_ν < 0.1 eV/c², Spin = ½, Charge = 0 eV/c² (Mass Limit) Nuclear & Particle Physics

Neutrino Oscillations

A quantum mechanical phenomenon in which a neutrino created with a specific lepton flavor changes flavor as it propagates through space.

P(ν_α → ν_β) = sin²(2θ) sin²(1.27 Δm² L / E) Probability (0 to 1) Astrophysics, Cosmology & Relativity

Neutron Star

An ultradense stellar core remnant produced by the core-collapse supernova explosion of a massive star, composed almost entirely of…

M ≈ 1.4–2.1 M_☉, R ≈ 10–12 km, ρ ≈ 10¹⁷ kg/m³ M_☉ (Mass), km (Radius) Classical Mechanics

Newton's First Law

The principle that an object remains at rest or continues in uniform motion in a straight line unless acted upon by a net external force.

∑ F = 0 ⇒ v = constant N/A Optics

Newton's Rings

An interference pattern of concentric bright and dark rings formed by an air film enclosed between a plano-convex lens and a flat glass…

r_m² = m λ R (Dark rings in reflection) m Classical Mechanics

Newton's Second Law

The law stating that net force acting on a body equals the rate of change of its linear momentum, simplified to mass times acceleration for…

F_net = m a N Classical Mechanics

Newton's Third Law

The law stating that whenever two objects interact, they exert forces on each other that are equal in magnitude and opposite in direction.

F_A_to_B = -F_B_to_A N Waves, Oscillations & Acoustics

Nodes & Antinodes

Specific fixed positions on a standing wave where displacement amplitude is zero (nodes) or maximum (antinodes).

Node Spacing = λ / 2, Antinode Spacing = λ / 2 m Classical Mechanics

Non-conservative Force

A force for which work done depends on the specific path taken, dissipating mechanical energy into heat, sound, or internal energy.

W_non-cons = ΔME = ΔKE + ΔPE N Waves, Oscillations & Acoustics

Non-linear Oscillations

Oscillatory systems where restoring forces do not obey linear Hooke's law, leading to amplitude-dependent frequency and chaotic behavior.

m (d²x/dt²) + k x + β x³ = 0 (Duffing Equation) Various Plasma Physics

Non-Neutral Plasma

A plasma composed exclusively of a single species of charged particles (electrons, positrons, or single ions) without background charge…

n_e ≫ n_i (Pure Electron or Ion Plasma) Single-Species Charged Cloud Condensed Matter & Materials Physics

Non-Newtonian Fluids

Fluids whose shear viscosity changes depending on applied shear rate, stress magnitude, or shear history.

τ = K (du / dy)^n (n ≠ 1) Pa·s (Apparent Viscosity η) Mathematical & Computational Physics

Nonlinear Dynamics

The study of physical systems governed by non-linear equations where output changes are not directly proportional to input changes.

d x / dt = f(x) (where f is non-linear) Phase Space Dynamics Classical Mechanics

Normal Force

The perpendicular contact force exerted by a surface on an object pressing against it.

N = m g cos θ N Waves, Oscillations & Acoustics

Normal Modes

Characteristic independent natural patterns of motion in which all parts of an oscillating system move sinusoidally at the same natural…

f_n = n f1 = n v / (2 L) Hz Nuclear & Particle Physics

Nuclear Binding Energy

The minimum energy required to completely disassemble an atomic nucleus into its constituent protons and neutrons.

E_b = Δm c² = [Z m_p + (A - Z) m_n - M_nucleus] c² MeV (Mega-electronvolts) Nuclear & Particle Physics

Nuclear Fission

A nuclear reaction in which a heavy nucleus splits into two or more smaller daughter nuclei accompanied by the release of neutrons and…

¹₀n + ²³⁵₉₂U → ²³⁶₉₂U* → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3 ¹₀n + Q (~200 MeV) MeV (Mega-electronvolts)