Pancyprian Technical School Physics (4-hour) flashcards

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

Centripetal acceleration

The acceleration of a body moving in a circle at constant speed, directed toward the centre, of magnitude v²/r or ω²r. It changes direction of velocity, not speed.

Work–energy theorem

The net work done on a body equals its change in kinetic energy: W_net = ½mv² − ½mu². Work by friction is included as negative and reduces kinetic energy.

Conservation of momentum

If the net external force on a system is zero, total linear momentum stays constant. This applies to collisions and explosions where internal forces dominate.

Terminal velocity

The steady speed reached when drag equals the driving force. For a sphere falling in fluid, 6πηrv = (ρ_sphere − ρ_fluid)Vg, so terminal speed grows with radius squared.

Archimedes' principle

The upthrust on a body in fluid equals the weight of fluid displaced. A floating body displaces a volume whose weight equals its own weight.

Bernoulli's equation

For steady, non-viscous, incompressible flow along a streamline, p + ½ρv² + ρgh is constant. Faster flow corresponds to lower pressure at equal height.

Young's modulus

The ratio of tensile stress to tensile strain in the linear elastic region: E = (F/A)/(Δl/l). It has units of pascals and is a property of the material.

Simple harmonic motion

Oscillation in which acceleration is proportional to displacement from equilibrium and oppositely directed: a = −ω²x. Period is independent of amplitude.

Pendulum period

For small oscillations (θ under about 10°), T = 2π√(l/g). The period depends on length and gravitational field strength, not on the bob mass.

Kepler's third law

The square of orbital period is proportional to the cube of orbital radius: T² = 4π²r³/(GM). It follows from equating gravitational and centripetal force.

Escape velocity

The minimum launch speed for a body to escape a mass's gravity without further propulsion: v = √(2GM/R). For Earth this is about 11.2 km/s.

Ideal gas equation

pV = nRT relates pressure, volume, amount and absolute temperature of an ideal gas, with R = 8.31 J/(mol·K). Temperature must always be in kelvin.

Specific latent heat

The energy needed to change the phase of one kilogram of a substance at constant temperature: Q = mL. No temperature change occurs during the change.

First law of thermodynamics

ΔU = Q − W, where Q is heat added to the system and W is work done by it. Internal energy of an ideal gas depends only on temperature.

Relative humidity

The ratio of the partial pressure of water vapour in air to the saturated vapour pressure at that temperature, expressed as a percentage.

Coulomb's law

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation: F = kQ₁Q₂/r².

Capacitance

The charge stored per unit potential difference: C = Q/V, measured in farads. For parallel plates C = ε₀ε_rA/d, and stored energy is ½CV².

Kirchhoff's loop rule

Around any closed circuit loop, the sum of EMFs equals the sum of potential drops (ΣIR). It expresses conservation of energy in a circuit.

Internal resistance

Resistance inside a source that causes terminal voltage to fall as current rises: V = ε − Ir. Maximum power transfers to a load when R = r.

Fleming's left-hand rule

Predicts the direction of force on a current-carrying conductor in a magnetic field: first finger field, second current, thumb force, all mutually perpendicular.

Faraday's law

The induced EMF equals the negative rate of change of magnetic flux linkage: ε = −N dΦ/dt. Faster flux change gives a larger induced EMF.

Lenz's law

The direction of an induced current is such that it opposes the change in flux producing it. This follows from conservation of energy.

Total internal reflection

Occurs when light travelling from a denser to a less dense medium exceeds the critical angle, where sinθ_c = n₂/n₁. No light is refracted out.

Doppler effect

The observed frequency of a wave changes when source and observer move relative to each other. Approach raises frequency; recession lowers it.

Stationary wave harmonics

A string fixed at both ends supports f_n = nv/(2L). A pipe closed at one end supports only odd harmonics, f_n = nv/(4L).

Photoelectric equation

hf = W + KE_max, where W is the work function. Emission occurs only above the threshold frequency, regardless of intensity.

Half-life

The time for half the nuclei in a sample to decay: T½ = ln2/λ. Activity and undecayed nuclei both halve in each half-life.

de Broglie wavelength

The wavelength associated with a particle of momentum p: λ = h/p = h/(mv). Electron diffraction experiments confirm this wave behaviour.

Combining uncertainties

For sums and differences, add absolute uncertainties. For products, quotients and powers, add percentage uncertainties, multiplying by the power.

Systematic versus random error

Systematic errors shift all readings the same way, as with a zero error. Random errors scatter both ways and are reduced by repeating and averaging.

Carnot efficiency limit

No heat engine operating between hot and cold reservoirs can exceed η = 1 − T_cold/T_hot, with temperatures in kelvin. Real engines fall below this.

Pascal's principle

Pressure applied to an enclosed fluid is transmitted undiminished throughout it. Hydraulic systems use F₁/A₁ = F₂/A₂ to multiply force.