OAE Physics (035) flashcards

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

Falsifiability

A hypothesis is scientific only if some conceivable observation could prove it wrong. Claims that cannot be tested or contradicted by any evidence fall outside empirical science.

Accuracy versus precision

Accuracy is how close a measurement is to the accepted value; precision is how closely repeated measurements agree with each other. A set can be precise yet inaccurate if a systematic error is present.

Systematic versus random error

Systematic error shifts every reading in the same direction, as from a miszeroed instrument. Random error scatters readings unpredictably in both directions and is reduced by averaging repeated trials.

Significant figure rules

All nonzero digits count, interior zeros count, leading zeros do not, and trailing zeros count only after a decimal point. Products keep the fewest sig figs; sums keep the fewest decimal places.

Scientific theory

A broad, repeatedly tested explanation supported by many independent lines of evidence, such as evolution or plate tectonics. It is not a guess and is not the same as a hypothesis.

Constant-acceleration kinematics

For acceleration that stays constant, v = v₀ + at, Δx = v₀t + ½at², and v² = v₀² + 2aΔx. These equations fail when acceleration varies with time.

Projectile motion components

Horizontal velocity stays constant because no horizontal force acts, while vertical motion accelerates at g downward. The two components are independent, and flight time depends only on vertical motion.

Static versus kinetic friction

Static friction adjusts up to a maximum μ_sN and prevents sliding; kinetic friction equals μ_kN and acts opposite the sliding motion. Usually μ_s exceeds μ_k for the same surfaces.

Centripetal force

Any net force directed toward the center of a circular path produces centripetal acceleration v²/r. Its magnitude is mv²/r; it is a role played by real forces, not a new kind of force.

Elastic versus inelastic collisions

Momentum is conserved in every isolated collision. Kinetic energy is also conserved only in elastic collisions; in perfectly inelastic collisions the objects stick together and lose the most kinetic energy.

Work–energy theorem

The net work done on an object equals its change in kinetic energy. This lets you relate forces and displacements directly to speed changes without solving for time.

Kepler's third law

The square of an orbital period is proportional to the cube of the semi-major axis, T² ∝ r³. Combined with gravitation it yields circular orbital speed v = √(GM/r).

Coulomb's law

The electric force between two point charges is kq₁q₂/r², directed along the line joining them. Like charges repel, opposite charges attract, and doubling distance quarters the force.

Electric potential difference

Potential difference is work per unit charge moved between two points, V = W/q, measured in volts. Positive charge naturally moves from higher to lower potential.

Series and parallel resistors

In series, resistances add and current is shared identically; in parallel, reciprocals add and voltage is identical across branches. Parallel branches always lower the equivalent resistance.

Ohm's law and power

For a resistor at constant temperature, V = IR. Power dissipated is P = IV, equivalently I²R or V²/R, so doubling current quadruples the heating in a fixed resistor.

Kirchhoff's circuit rules

The junction rule states charge is conserved, so current entering a node equals current leaving. The loop rule states energy is conserved, so potential changes around any closed loop sum to zero.

Capacitor energy storage

A capacitor stores charge Q = CV and energy U = ½CV². For a parallel-plate capacitor C = ε₀A/d, so larger plates or a smaller gap increase capacitance.

Magnetic force on moving charge

A charge moving in a magnetic field feels F = qvB sin θ, perpendicular to both velocity and field. It does no work, so it changes direction but not speed.

Faraday and Lenz laws

A changing magnetic flux induces an emf equal to −N ΔΦ/Δt. Lenz's law fixes the direction: the induced current creates a field opposing the change that produced it.

Wave speed relation

For any periodic wave, speed equals frequency times wavelength, v = fλ. Frequency is fixed by the source, so entering a slower medium shortens the wavelength.

Doppler effect

Observed frequency increases when source and observer approach and decreases when they recede. The shift depends on relative motion and, for sound, on motion relative to the air.

Standing waves on strings

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

Snell's law

Refraction obeys n₁ sin θ₁ = n₂ sin θ₂, where n = c/v. Light bends toward the normal when entering a higher-index medium and away when entering a lower-index one.

Total internal reflection

Light in a denser medium reflects completely when the incidence angle exceeds the critical angle θ_c = sin⁻¹(n₂/n₁). It requires travel from higher to lower refractive index.

Thin lens equation

1/f = 1/d_o + 1/d_i with magnification m = −d_i/d_o. A negative image distance denotes a virtual image on the same side as the object for a converging lens.

Double-slit interference

Bright fringes occur where path difference d sin θ equals a whole number of wavelengths, mλ. Fringe spacing on a distant screen is approximately λL/d.

Calorimetry equations

Heat for a temperature change is Q = mcΔT; heat for a phase change is Q = mL, applied at constant temperature. In an insulated system, heat lost equals heat gained.

First law of thermodynamics

ΔU = Q − W for work done by the system. Internal energy rises with heat added and falls with work done by the gas; in a cycle ΔU is zero.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature, with R = 8.31 J/(mol·K). Temperature must be in kelvin, and at fixed volume pressure scales with temperature.

Carnot efficiency limit

No engine between reservoirs at T_H and T_C can exceed e = 1 − T_C/T_H, with temperatures in kelvin. Real engines fall short because of friction and irreversible heat flow.

Photoelectric effect

Electrons are ejected only when photon frequency exceeds a threshold set by the work function φ. Maximum kinetic energy is hf − φ, independent of light intensity.

de Broglie wavelength

Every particle has wavelength λ = h/p, where p is momentum. The wave nature is measurable for electrons and neutrons but negligible for everyday objects.

Radioactive half-life

Half-life is the time for half the nuclei in a sample to decay, related to the decay constant by t₁/₂ = 0.693/λ. After n half-lives, the fraction remaining is (1/2)ⁿ.