Slovak Physics Olympiad Cat A flashcards

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

Lorentz factor

Quantity γ = 1/√(1 − v²/c²) that appears in relativistic transformations. It equals 1 at rest and grows without bound as speed approaches the speed of light.

de Broglie wavelength

Wavelength assigned to a particle with momentum p, given by λ = h/p. It explains electron diffraction and sets the scale at which wave behaviour becomes observable.

Photoelectric threshold frequency

Minimum frequency f0 = W/h at which photons can eject electrons from a metal of work function W. Below it, no emission occurs regardless of light intensity.

Half-life

Time T½ = ln2/λ after which half of the radioactive nuclei in a sample remain. It is independent of the initial number of nuclei and of chemical state.

Carnot efficiency

Maximum efficiency of a heat engine operating between absolute temperatures T_hot and T_cold, equal to 1 − T_cold/T_hot. No real engine between those reservoirs exceeds it.

First law of thermodynamics

Energy conservation for thermal processes: ΔU = Q − W, where Q is heat added to the system and W is work done by the system on its surroundings.

Mean free path

Average distance a gas molecule travels between collisions, λ = kT/(√2·πd²p). It decreases with rising pressure and increases with rising temperature.

Adiabatic process

Process with no heat exchange (Q = 0), obeying pV^κ = constant for an ideal gas. Work done comes entirely from the internal energy change.

Latent heat of fusion

Heat per unit mass needed to melt a solid at its melting point without changing temperature, Q = mL. It breaks the ordered lattice rather than raising kinetic energy.

Doppler effect for sound

Change in observed frequency when source and observer move relative to the medium, f' = f(v ± v_o)/(v ∓ v_s). Approach raises pitch, recession lowers it.

Standing wave nodes

Points of zero displacement in a standing wave, separated by half a wavelength. Adjacent antinodes, where amplitude is maximal, lie midway between nodes.

Resonance frequency of LC circuit

Frequency f = 1/(2π√(LC)) at which inductive and capacitive reactances cancel. At resonance the impedance is purely resistive and current amplitude is maximal.

Faraday's law of induction

Induced emf equals the negative rate of change of magnetic flux through a circuit, ε = −dΦ/dt. The minus sign expresses Lenz's law opposing the change.

Kirchhoff's loop rule

Sum of potential differences around any closed circuit loop is zero, expressing energy conservation. It is applied together with the node rule for currents.

Total internal reflection

Complete reflection at a boundary when light travels from denser to rarer medium beyond the critical angle, sinθ_c = n2/n1. No refracted ray emerges.

Young's double-slit spacing

Distance between adjacent bright fringes on a screen, Δy = λL/d, for slit separation d and screen distance L. It grows with wavelength and screen distance.

Brewster angle

Angle of incidence tanθ_B = n2/n1 at which reflected light is completely polarized perpendicular to the plane of incidence. The reflected and refracted rays are then perpendicular.

Diffraction grating equation

Principal maxima occur where d·sinθ = mλ, with d the grating spacing and m the order. Larger grating spacing gives more closely packed maxima.

Simple harmonic motion condition

Motion where restoring acceleration is proportional and opposite to displacement, a = −ω²x. The period then does not depend on amplitude.

Beat frequency

Frequency of loudness variation when two tones of close frequencies f1 and f2 superpose, equal to |f1 − f2|. It arises from alternating constructive and destructive interference.

Kepler's third law

Square of orbital period is proportional to cube of semi-major axis, T² = 4π²a³/(GM). The constant depends only on the central body's mass.

Work–energy theorem

Net work done on a body equals its change in kinetic energy, W_net = ½mv² − ½mv0². It holds for variable forces when net work is computed by integration.

Bernoulli equation

For steady ideal flow, p + ½ρv² + ρgh is constant along a streamline. Faster flow at lower height therefore corresponds to lower pressure.

Moment of inertia

Quantity I = Σmr² describing resistance to angular acceleration about a chosen axis. Rotational kinetic energy is ½Iω² and torque obeys τ = Iα.

Standard uncertainty of the mean

For N independent readings with sample standard deviation s, the mean's uncertainty is s/√N. Averaging more readings reduces random but not systematic error.

Error propagation for products

For z = x·y, relative uncertainties add in quadrature: σz/z = √((σx/x)² + (σy/y)²). For division the same rule applies to the quotient.

Linearization of data

Transforming measured variables so the expected relation becomes a straight line, letting the slope yield a physical constant. An example is plotting T² against length for a pendulum.

Systematic versus random error

Systematic errors shift all readings consistently and are not reduced by averaging; random errors scatter about a mean and decrease with repeated measurements.

Relativistic energy–momentum relation

Total energy satisfies E² = (pc)² + (mc²)², valid for all speeds. For a photon, mass is zero so E = pc.

Electric potential of a point charge

Potential V = kq/r at distance r from a point charge, taking zero at infinity. Electric field is the negative gradient of potential.

Magnetic force on a moving charge

Force F = qv × B, perpendicular to both velocity and magnetic field. It does no work, so it changes direction but not speed.

Buoyant force

Upward force on a submerged or floating body equal to the weight of displaced fluid, F = ρ_fluid·V_displaced·g. A floating body displaces its own weight of fluid.