ORELA Physics (NT308) flashcards

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

SI base units

The seven units - meter, kilogram, second, ampere, kelvin, mole and candela - from which all other SI units are built; for example, the newton equals kg·m/s².

Accuracy versus precision

Accuracy measures how close a result lies to the accepted value; precision measures how closely repeated measurements agree with one another, whether or not they are correct.

Random versus systematic error

Random error scatters readings above and below the true value and shrinks when trials are averaged; systematic error shifts every reading the same way, as from a miscalibrated instrument.

Dimensional analysis

Checking that both sides of an equation reduce to the same base units; a mismatch proves the equation wrong, and matching dimensions can suggest the form of an unknown relationship.

Falsifiability in science

A hypothesis must make predictions that observation could show to be false; claims that cannot be tested against evidence fall outside the scope of scientific inquiry.

Newton's second law

The net force on an object equals its mass times its acceleration, ΣF = ma; acceleration points along the net force and is inversely proportional to the mass.

Newton's third law pair

For every force on one body there is an equal and opposite force on a different body; the two forces act on separate objects, so they never cancel each other.

Conservation of momentum

When the net external force on a system is zero, total momentum Σmv stays constant; this holds for collisions and explosions, including inelastic ones that lose kinetic energy.

Work-energy theorem

The net work done on an object equals its change in kinetic energy, W_net = ΔKE; work is Fd cosθ, counting only the force component along the displacement.

Centripetal acceleration

An object moving in a circle at constant speed accelerates toward the center with a = v²/r; whatever real force provides the net inward force is the centripetal force.

Moment of inertia

The rotational analog of mass, I = Σmr², measuring resistance to angular acceleration; it depends on how mass is distributed, so one object has different values about different axes.

First law of thermodynamics

The change in internal energy equals heat added minus work done by the system, ΔU = Q − W; internal energy is a state function while heat and work depend on the path.

Carnot efficiency

The maximum efficiency possible for a heat engine operating between a hot and a cold reservoir is 1 − T_c/T_h, with temperatures in kelvin; no real engine reaches this limit.

Ideal gas law

PV = nRT relates pressure, volume, moles and absolute temperature, with R = 8.314 J/(mol·K); temperature must be in kelvin or the relation fails.

Latent heat

Energy absorbed or released during a phase change at constant temperature, Q = mL; the latent heat of fusion melts ice and that of vaporization boils water without raising temperature.

RMS molecular speed

v_rms = √(3kT/m) = √(3RT/M) is the square root of the mean squared speed of gas molecules; it increases with temperature and decreases for heavier molecules.

Snell's law

n₁ sin θ₁ = n₂ sin θ₂ relates the angles of incidence and refraction at an interface; light bends toward the normal on entering a higher-index medium because it slows down there.

Total internal reflection

When light travelling in a denser medium strikes a boundary beyond the critical angle, sin θ_c = n₂/n₁, none refracts out and the ray is entirely reflected back inside.

Doppler effect

A moving source or observer shifts the observed frequency according to f′ = f(v ± v_o)/(v ∓ v_s); approach raises the observed frequency and recession lowers it.

Standing wave harmonics

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

Thin lens equation

1/f = 1/d_o + 1/d_i with magnification m = −d_i/d_o; positive magnification means an upright image, negative means inverted, and negative image distance means virtual.

Coulomb's law

The force between two point charges is F = kq₁q₂/r² with k = 8.99×10⁹ N·m²/C²; like charges repel, opposite charges attract, and the force follows an inverse-square law.

Electric field lines

Lines drawn to begin on positive charge and end on negative charge; their density indicates field strength, they never cross, and they point along the field direction.

Series circuit rules

There is only one path, so the current is identical through every element, the resistances add to give total resistance, and the source voltage divides in proportion to resistance.

Parallel circuit rules

With several branches, the voltage is the same across each, the branch currents add, and total resistance is less than the smallest branch, found from 1/R = Σ1/Rᵢ.

Lenz's law

An induced current flows in the direction whose magnetic field opposes the change in flux that produced it; this follows from energy conservation and sets the sign in Faraday's law.

Magnetic force on moving charge

F = qvB sin θ acts perpendicular to both the velocity and the field; being perpendicular to the motion, it changes direction without doing work or changing speed.

Photoelectric effect

Light ejects electrons from a metal only above a threshold frequency, with maximum kinetic energy K = hf − φ; greater intensity increases current but not electron energy.

de Broglie wavelength

Every particle has a wavelength λ = h/p; it is measurable for electrons and other tiny masses and explains electron diffraction as well as quantized atomic energy levels.

Half-life

The time for half the nuclei in a radioactive sample to decay; after n half-lives the fraction remaining is (1/2)^n, and decay is random so predictions are statistical.

Mass defect and binding energy

A nucleus has less mass than its separated nucleons; the missing mass multiplied by c² gives the binding energy holding it together, about 931.5 MeV per atomic mass unit.

Time dilation

A clock moving relative to an observer runs slow by Δt = γΔt₀ with γ = 1/√(1 − v²/c²); the effect is negligible at everyday speeds and grows sharply near light speed.