IB Physics SL flashcards

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

Absolute uncertainty of a reading

Half the smallest scale division for an analogue instrument; for a digital meter, it equals the place value of the last displayed digit.

Combining uncertainties in multiplication

When quantities are multiplied or divided, their fractional uncertainties add, so percentage uncertainties are summed to give the result's percentage uncertainty.

Scalar versus vector

A scalar has magnitude only, such as mass or energy; a vector has magnitude and direction, such as displacement, velocity, acceleration and force.

Linearising a graph

Plotting the variables so the relationship becomes a straight line, for example y against x² when y = kx², lets the gradient give the constant.

Newton's second law

The resultant force on a body equals the product of its mass and acceleration, F = ma, with acceleration in the direction of the resultant force.

Conservation of momentum

In the absence of an external resultant force, the total momentum of a system stays constant through collisions and explosions, even when kinetic energy is lost.

Impulse

Impulse equals force multiplied by the time it acts, FΔt, and equals the change in momentum; it is the area under a force–time graph.

Elastic potential energy

Energy stored in a stretched or compressed spring, given by ½kx² for a material obeying Hooke's law, and equal to the area under a force–extension graph.

Internal energy

The total random kinetic energy and intermolecular potential energy of the particles making up a substance, which changes with temperature and phase.

Specific latent heat

The energy needed to change the phase of one kilogram of a substance at constant temperature, given by Q = mL for melting or boiling.

Ideal gas equation

For an ideal gas, pressure times volume equals the number of moles times the gas constant times absolute temperature, pV = nRT.

First law of thermodynamics

The change in internal energy of a system equals the heat added to it minus the work done by it, ΔU = Q − W.

Simple harmonic motion

Oscillation in which acceleration is proportional to displacement from equilibrium and directed toward it, a = −ω²x, giving a sinusoidal displacement–time graph.

Standing wave on a string

A wave pattern formed by two oppositely travelling waves of equal frequency, with nodes and antinodes; wavelengths allowed are λ = 2L/n for fixed ends.

Doppler effect

The change in observed frequency when a source and observer move relative to each other; approach raises frequency, recession lowers it.

Snell's law

For light crossing a boundary, n₁sinθ₁ = n₂sinθ₂, where angles are measured from the normal and n is the refractive index.

Kirchhoff's circuit laws

The sum of currents entering a junction equals the sum leaving, and around any closed loop the sum of emf values equals the sum of potential differences.

Internal resistance

Resistance inside a source that causes the terminal voltage to fall below the emf when current flows, V = ε − Ir.

Faraday's law of induction

The induced emf in a coil equals the negative rate of change of magnetic flux linkage, ε = −NΔΦ/Δt, with direction set by Lenz's law.

Magnetic force on a charge

A charge q moving with speed v at angle θ to a magnetic field B experiences force F = qvB sinθ, perpendicular to both velocity and field.

Centripetal acceleration

The acceleration of a body moving in a circle, directed toward the centre, with magnitude v²/r or ω²r.

Newton's law of gravitation

The gravitational attraction between two point masses is proportional to the product of the masses and inversely proportional to the square of their separation, F = Gm₁m₂/r².

Orbital period

For a circular orbit, the period squared is proportional to the orbital radius cubed, T² = (4π²/GM)r³, following from equating gravitational and centripetal force.

Geostationary orbit

A circular equatorial orbit with a 24-hour period, so the satellite stays above the same point on Earth's surface; used for communication.

Photoelectric effect

Emission of electrons from a metal surface when light of frequency above a threshold strikes it; maximum kinetic energy equals hf minus the work function.

Photon energy

The energy carried by one photon, E = hf = hc/λ, where h is Planck's constant and f is the frequency of the radiation.

Half-life

The time for half the nuclei in a radioactive sample to decay, related to the decay constant by t½ = ln2/λ.

Beta-minus decay

A neutron in the nucleus converts to a proton, emitting an electron and an antineutrino; proton number rises by one while nucleon number is unchanged.

Binding energy per nucleon

The energy equivalent of the mass defect divided by the number of nucleons; it peaks near iron-56, so fission of heavy nuclei and fusion of light nuclei release energy.

Specific energy of a fuel

The energy released per unit mass of fuel when it is burned or reacted, used to compare energy sources.

Wind power available

The power in moving air intercepted by a turbine is about ½ρAv³, so doubling wind speed increases available power eightfold.

Hydroelectric power

Power generated from falling water equals ρgQh, where Q is the volume flow rate, h the head, ρ the water density and g gravity.