BCS Written Physics flashcards

32 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 a body equals the rate of change of its momentum; for constant mass this reduces to F = ma, with force in newtons.

Work-energy theorem

The net work done on a particle equals its change in kinetic energy, so W_net = ½mv² − ½mu², valid for any path.

Escape velocity

The minimum launch speed needed to escape a body's gravity without further propulsion: v_e = √(2GM/R), about 11.2 km/s from Earth's surface.

Bernoulli's equation

For steady, incompressible, non-viscous flow along a streamline, pressure plus kinetic and gravitational potential energy densities stays constant: P + ½ρv² + ρgh = constant.

Young's modulus

The ratio of tensile stress to tensile strain for a material in its linear elastic region, a measure of stiffness with units of pascals.

Surface tension

The force per unit length acting along a liquid surface, arising from unbalanced molecular attraction, which makes droplets spherical and supports small objects.

First law of thermodynamics

Energy conservation for thermal systems: the heat added to a system equals the increase in internal energy plus the work done by the system.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs: η = 1 − T_c/T_h, with absolute temperatures in kelvin.

Standing wave condition

A string fixed at both ends supports standing waves only when twice its length is an integer multiple of the wavelength, giving f = nv/(2L).

Doppler effect

The change in observed frequency when source and observer move relative to each other; approach raises frequency, recession lowers it, for sound and light alike.

Total internal reflection

When light travelling in a denser medium strikes a boundary beyond the critical angle, it reflects entirely back, with no refracted ray, as in optical fibres.

Snell's law

The ratio of the sines of the angles of incidence and refraction equals the ratio of refractive indices of the two media: n₁sinθ₁ = n₂sinθ₂.

Ohm's law

For a conductor at constant temperature, current is proportional to potential difference: V = IR, where R is resistance in ohms.

Kirchhoff's laws

At any junction charge is conserved so currents sum to zero; around any closed loop the sum of emfs equals the sum of potential drops.

Faraday's law of induction

A changing magnetic flux through a circuit induces an emf equal to the negative rate of change of flux, the minus sign expressing Lenz's law.

Lorentz force

The force on a charge moving in electric and magnetic fields: F = qE + qv × B, perpendicular to velocity for the magnetic part.

Half-life

The time for half the nuclei in a radioactive sample to decay; it equals ln2 divided by the decay constant and is independent of sample size.

Mass defect

The difference between the mass of a nucleus and the sum of its constituent masses, appearing as binding energy according to E = Δmc².

Photoelectric effect

Emission of electrons from a metal surface when light above a threshold frequency strikes it, evidence that light delivers energy in discrete photons.

de Broglie wavelength

Every particle has an associated wavelength equal to Planck's constant divided by its momentum, observable for electrons and other small masses.

Time dilation

A clock moving relative to an observer runs slow by the factor γ = 1/√(1 − v²/c²), an effect confirmed by muon lifetimes and atomic clocks.

Heisenberg uncertainty principle

Position and momentum cannot both be known precisely at once; their uncertainties satisfy ΔxΔp ≥ ħ/2, a fundamental limit not a measurement flaw.

Bragg's law

X-rays reflected from successive crystal planes interfere constructively when 2d sinθ = nλ, allowing plane spacing d to be measured.

Fermi energy

The energy of the highest occupied electron state in a solid at absolute zero; its position relative to band edges determines metallic or insulating behaviour.

Diode equation

The current through a p–n junction varies with applied voltage as I = I₀(e^(eV/k_BT) − 1), rising sharply in forward bias.

Transistor current gain

For a bipolar transistor in active mode, the collector current divided by base current, denoted β, typically 50 to 300 for small-signal devices.

Gauss's theorem

The flux of a vector field through a closed surface equals the volume integral of its divergence, linking surface and volume descriptions of fields.

Newton-Raphson method

An iterative root-finding scheme using x_new = x − f(x)/f'(x); it converges quadratically near a simple root but can fail if the derivative vanishes.

Falsifiability

The requirement that a scientific hypothesis make predictions capable of being shown wrong by observation; unfalsifiable claims lie outside empirical science.

Systematic versus random error

Systematic error shifts all readings the same way and is not reduced by averaging; random error scatters readings and falls as more are averaged.

Vernier least count

The smallest measurement a vernier instrument can resolve, found as one main-scale division minus one vernier-scale division, often 0.1 mm.

Fractional uncertainty rule

When quantities are multiplied or divided, their fractional uncertainties add; when raised to a power n, the fractional uncertainty is multiplied by n.