AAPT NCPT (Level 1) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Newton's second law

The net force on an object equals its mass times its acceleration. It holds only in inertial reference frames and relates force, mass, and acceleration vectorially.

Centripetal acceleration

An object moving in a circle of radius r at speed v has acceleration v²/r directed toward the center. Speed may be constant while velocity changes direction.

Conservation of momentum

If the net external impulse on a system is zero, total momentum stays constant. This applies component by component and underlies collision analysis.

Elastic collision

A collision in which both momentum and kinetic energy are conserved. Objects bounce apart; in perfectly inelastic collisions they stick and lose maximum kinetic energy.

Simple harmonic motion

Oscillation with restoring acceleration proportional to displacement and opposite in direction, a = −ω²x. Angular frequency is √(k/m) for springs and √(g/L) for pendulums.

First law of thermodynamics

The change in internal energy equals heat added to the system minus work done by the system: ΔU = Q − W, with signs defined by the chosen convention.

Ideal gas law

Relates pressure, volume, and temperature: PV = nRT = NkT. It assumes negligible molecular volume and no intermolecular forces.

Root-mean-square speed

The typical molecular speed v_rms = √(3kT/m). At equal temperatures, lighter molecules have higher rms speeds than heavier ones.

Adiabatic process

A process with no heat exchange, Q = 0, so ΔU = −W. For an ideal gas, PV^γ remains constant, with γ = C_p/C_v.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs: η = 1 − T_c/T_h, using absolute temperatures. No real engine exceeds it.

Wave speed relation

For any periodic wave, speed equals frequency times wavelength, v = fλ. On a stretched string, v also equals √(T/μ).

Standing waves on a string

A string fixed at both ends supports frequencies f_n = nv/(2L). The fundamental has one antinode; each higher harmonic adds one more antinode.

Snell's law

Refraction obeys n₁ sinθ₁ = n₂ sinθ₂. Light bends toward the normal entering a higher-index medium and away from it entering a lower-index medium.

Total internal reflection

Occurs when light travels from higher to lower refractive index at angles beyond the critical angle, where sinθ_c = n₂/n₁. No refracted ray emerges.

Thin lens equation

Relates focal length, object distance, and image distance: 1/f = 1/d_o + 1/d_i. Magnification is m = −d_i/d_o; negative m indicates an inverted image.

Double-slit interference

Bright fringes occur where path difference d sinθ = mλ. Fringe spacing on a distant screen is approximately λL/d.

Coulomb's law

The force between point charges is kq₁q₂/r², directed along the line joining them. Like charges repel, opposite charges attract.

Electric field definition

Electric field is force per unit charge, E = F/q, pointing in the direction a positive test charge would be pushed. Field lines never cross.

Ohm's law and power

For ohmic resistors, V = IR. Power dissipated can be written P = IV = I²R = V²/R, useful when one quantity is fixed.

Series and parallel resistors

Series resistances add: R_eq = ΣR, with common current. Parallel conductances add: 1/R_eq = Σ1/R, with common voltage across branches.

Kirchhoff's rules

The junction rule states charge is conserved at nodes; the loop rule states total voltage change around any closed loop is zero. Together they solve circuits.

Magnetic force on moving charge

A charge q moving at velocity v in field B feels force qvB sinθ, perpendicular to both v and B. It does no work and cannot change speed.

Faraday's law of induction

An induced emf equals the negative rate of change of magnetic flux, −dΦ_B/dt. Lenz's law sets the induced current direction to oppose the flux change.

Photon energy

A photon carries energy E = hf = hc/λ. Using hc ≈ 1240 eV·nm quickly gives photon energies for visible and ultraviolet light.

Photoelectric effect

Electrons eject from a metal when light exceeds a threshold frequency. Maximum kinetic energy is K_max = hf − φ, where φ is the work function.

de Broglie wavelength

Matter has an associated wavelength λ = h/p. Higher momentum means shorter wavelength, observable for electrons but negligible for macroscopic objects.

Radioactive half-life

The time for half of a sample to decay, t₁/₂ = ln2/λ ≈ 0.693/λ. Activity follows N = N₀e^(−λt) and decreases by half each half-life.

Mass-energy equivalence

Mass and energy are related by E = mc². Nuclear reactions convert small mass differences into energy, with 1 u equivalent to about 931.5 MeV.

Bohr energy levels

Hydrogen levels follow E_n = −13.6 eV/n². A transition emits or absorbs a photon whose energy equals the level difference.

Accuracy versus precision

Accuracy measures closeness to the true value; precision measures repeatability among trials. Systematic errors hurt accuracy, while random errors limit precision.

Propagation of uncertainty

For sums, absolute uncertainties add in quadrature. For products and quotients, fractional uncertainties add in quadrature to give the result's fractional uncertainty.

Standard error of the mean

The spread of an average is s/√N, where s is the sample standard deviation and N the number of trials. Averaging reduces random error by √N.

Systematic error

A consistent bias that shifts measurements in one direction, such as miscalibration or zero offset. It is not reduced by repeated trials and requires correction or recalibration.