OSAT Physics (OK114) flashcards

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

Accuracy versus precision

Accuracy describes how close a measurement is to the accepted value; precision describes how closely repeated measurements agree with one another. Systematic error harms accuracy, random error harms precision.

Hypothesis

A testable, falsifiable proposed explanation for an observation. It must make predictions that a controlled experiment could confirm or refute; unfalsifiable claims fall outside science.

Significant figures rule

For multiplication and division, round the result to the least number of significant figures among the inputs. For addition and subtraction, keep the least number of decimal places.

Dimensional analysis

A method of checking equations and converting units by treating units as algebraic quantities. Both sides of a valid equation must reduce to identical base units.

Constant-acceleration kinematics

The equations v = v0 + at, Δx = v0t + ½at², and v² = v0² + 2aΔx describe motion with constant acceleration. They fail whenever acceleration changes during the interval.

Projectile motion

Two-dimensional motion under gravity alone. Horizontal velocity stays constant while vertical acceleration is g downward, so time of flight depends only on the vertical component.

Centripetal force

The net inward force required to keep an object moving in a circle, equal to mv²/r. It is supplied by tension, gravity, friction, or a normal force, not by an outward force.

Static versus kinetic friction

Static friction adjusts up to a maximum μsN to prevent sliding. Once sliding begins, kinetic friction has a fixed value μkN and opposes the relative motion.

Work-energy theorem

The net work done on an object equals its change in kinetic energy, Wnet = ΔKE = ½mvf² − ½mvi². It holds even when forces vary or the path is curved.

Conservation of momentum

When the net external impulse on a system is zero, total momentum Σmv stays constant. This holds in all collisions, elastic or inelastic, and in explosions.

Elastic collision

A collision in which both momentum and kinetic energy are conserved. Objects bounce apart; the coefficient of restitution equals one in the ideal case.

Power

The rate at which work is done or energy is transferred, P = W/t = Fv cos θ. The SI unit is the watt, equal to one joule per second.

First law of thermodynamics

The change in internal energy of a system equals heat added minus work done by the system, ΔU = Q − W. Energy is conserved when heat and work are both counted.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs, e = 1 − Tc/Th with temperatures in kelvin. No real engine can exceed it.

Latent heat

The energy per unit mass absorbed or released during a phase change at constant temperature, Q = mL. It does not raise temperature because it breaks intermolecular bonds.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature for an ideal gas, with R = 8.314 J/(mol·K). Temperature must be expressed in kelvin.

Doppler effect

The shift in observed frequency when a source and observer move relative to each other. Approach raises frequency and recedes lowers it; the effect applies to sound and light.

Snell's law

n1 sin θ1 = n2 sin θ2 describes refraction at an interface. Light bends toward the normal entering a denser medium and can totally internally reflect past the critical angle.

Standing wave harmonics

A string or open pipe supports all integer harmonics fn = nv/(2L). A pipe closed at one end supports only odd harmonics fn = nv/(4L).

Thin lens equation

1/f = 1/do + 1/di with magnification m = −di/do. A positive image distance on the far side of a converging lens means a real, inverted image.

Ohm's law

Current through a conductor is proportional to the potential difference across it, V = IR, provided temperature stays constant. Resistance is measured in ohms.

Series and parallel resistors

Series resistors share one current and add directly, Req = ΣR. Parallel resistors share one voltage and add reciprocally, 1/Req = Σ1/R.

Faraday's law of induction

A changing magnetic flux through a loop induces an emf equal to ε = −NΔΦ/Δt. The minus sign reflects Lenz's law opposing the change.

Kirchhoff's rules

The junction rule states currents into a node equal currents out, conserving charge. The loop rule states voltage changes around any closed loop sum to zero, conserving energy.

Photoelectric effect

Light ejects electrons from a metal only above a threshold frequency. Maximum kinetic energy equals hf minus the work function, evidence that light is quantized into photons.

de Broglie wavelength

Every particle has an associated wavelength λ = h/p = h/(mv). It is measurable for electrons and explains electron diffraction patterns.

Half-life

The time for half the nuclei in a radioactive sample to decay, related to the decay constant by t½ = 0.693/λ. Activity falls exponentially with time.

Alpha and beta decay

Alpha emission removes two protons and two neutrons, lowering A by 4 and Z by 2. Beta-minus emission converts a neutron to a proton, raising Z by 1 and leaving A unchanged.

Percent error

Percent error = |measured − accepted| / accepted × 100%. It quantifies the deviation of an experimental result from the accepted or theoretical value.

Linearizing a graph

Rearranging data so a relationship plots as a straight line, then extracting a constant from the slope. For a pendulum, plotting T² versus L gives slope 4π²/g.

Best-fit line slope

The slope of a best-fit line equals the change in the vertical variable per unit change in the horizontal variable, carrying units of y/x. It often yields a physical constant.

Acid dilution safety

Always add acid slowly to water while stirring, never water to concentrated acid. The dilution releases heat and adding water to acid can cause violent boiling and splattering.