ib physics definitions

Displacement (s)

distance traveled in a particular direction (change in position)

Speed (u,v)

rate of change of distance

Acceleration (a)

rate of change of velocity

Newton's First Law of Motion

An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.

Newton's Second Law of Motion

An unbalanced force will cause an object to accelerate in the direction of the net force. The acceleration of the object is proportional to the net force and inversely proportional to its mass. (Fnet \= ma or Fnet \= Δ p/Δ t (net force \= rate of change of momentum))

Newton's Third Law of Motion

When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A.

Linear Momentum (p)

product of mass and velocity

Impulse (J)

change in momentum

Law of Conservation of Linear Momentum

The total momentum of an isolated system (no external forces) remains constant.

Work (W)

The product of a force on an object and the displacement of the object in the direction of the force.

Principle of Conservation of Energy

The total energy of an isolated system (no external forces) remains constant. (OR - Energy can be neither created nor destroyed but only transformed from one form to another or transferred from one object to another.)

Elastic Collision

a collision in which kinetic energy is conserved

Power (P)

The rate at which work is done or the rate at which energy is transferred.

Efficiency (eff)

The ratio of the useful energy (or power or work) output to the total energy (or power or work) input.

Newton's Universal Law of Gravitation

The force of gravity between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centers.

Gravitational Field Strength (g)

gravitational force per unit mass on a point mass (g \= Fg / m)

Gravitational Potential Energy (EP)

the work done in moving a mass from infinity to a point in space (NOTE: the work done is path independent)

Gravitational Potential (V)

the work done per unit mass in moving a mass from infinity to a point in space

Escape Speed

minimum speed of a rocket needed to escape the gravitational attraction of a planet

Kepler's Third Law

the ratio of the orbital period squared to the average orbital radius cubed is constant for all planets

Temperature (T)

A measure of the average random kinetic energy of the particles of a substance.

Internal Energy of a substance (U)

The total potential energy and random kinetic energy of the molecules of the substance.

Thermal Energy (Heat) (Q)

Energy transferred between two substances in thermal contact due a temperature difference.

Mole

An amount of a substance that contains the same number of atoms as 0.012 kg of 12C.

Molar Mass

The mass of one mole of a substance.

Avogadro constant (NA)

The number of atoms in 0.012 kg of 12C ( \= 6.02 x 1023).

Thermal Capacity (C)

energy required to raise the temperature of a substance by 1K

Specific Heat Capacity (c)

energy required per unit mass to raise the temperature of a substance by 1K

Specific Latent Heat (L)

energy per unit mass absorbed or released during a phase change

Pressure (P)

force per unit area acting on a surface

Ideal Gas

a gas that follows the ideal gas equation of state (PV \= nRT) for all values of P, V, and T (an ideal gas cannot be liquefied)

First Law of Thermodynamics (U \= ΔU + W)

The thermal energy transferred to a system from its surroundings is equal to the work done by the system plus the change in internal energy of the system. (an application of the principle of conservation of energy)

Entropy

a system property that expresses the degree of disorder in the system

Second Law of Thermodynamics

The overall entropy of the universe is increasing.

Displacement (for waves)

distance a particle moves in a particular direction from its mean (equilibrium) position

Amplitude

maximum displacement from the mean position

Frequency (f)

number of oscillations per unit time

Period (T)

time taken for one complete oscillation (cycle) (OR: time taken for one cycle to pass a given point)

Phase Difference

difference in phase between two points

Simple Harmonic Motion

motion that takes place when the acceleration of an object is proportional to its displacement from its equilibrium position and is always directed toward its equilibrium position

Resonance

a transfer of energy in which a system is subject to an oscillating force that matches the natural frequency of the system resulting in a large amplitude of vibration

Wave Pulse

single oscillation or disturbance in a medium

Continuous Progressive (Traveling) Wave

series of periodic pulses

Transverse Wave

wave in which the direction of motion of the energy transfer (the wave) is perpendicular to the direction of motion of the particles of the medium (NOTE: light waves are transverse) (NOTE: transverse waves cannot be propagated in gases)

Longitudinal Wave

wave in which the direction of motion of the energy transfer (the wave) is parallel to the direction of motion of the particles of the medium (NOTE: sound waves are longitudinal)

Wavelength (λ)

shortest distance along the wave between two points in phase with one another (OR: distance traveled by the wave in one period)

Wave Speed (v)

speed of transfer of the energy of the wave

Intensity (I)

power received per unit area (NOTE: for a wave, its intensity is proportional to the square of its amplitude)

Snell's Law

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency.

Refractive Index (Index of Refraction) (n)

the ratio of the speed of the wave in the refracted medium to the speed of the wave in the incident medium

Principle of Superposition

When two waves meet, the resultant displacement is the vector sum of the displacements of the component waves.

Node

locations of constant complete destructive interference on a standing wave

Antinode

locations of maximum constructive interference on a standing wave

Doppler Effect

The change of frequency of a wave due to the movement of the source or the observer relative to the medium of wave transmission.

Rayleigh Criterion

When the central maximum of one diffraction pattern overlaps the first minimum of a second diffraction pattern, the two sources are "just resolved."

Polarized Light

light in which the electric field vector vibrates in one plane only

Brewster's Law

When light is incident on a surface at such an angle that the reflected and transmitted rays are perpendicular and the reflected ray is totally plane polarized, then the index of refraction of the substance is equal to the tangent of the angle of incidence. (n \= tan θi)

Polarizer

device that produces plane polarized light from an unpolarized beam

Analyzer

polarizer used to detect polarized light

Law of Conservation of Charge

The total electric charge of an isolated system remains constant.

Coulomb's Law

The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to square of the distance between them, and directed along the line joining the two charges. (F \= k q1 q2 / r2)

Electric Field Strength (E)

Electric force per positive unit test charge (E \= F/q)

Electric Potential (V)

work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V \= W/q) (V \= kq/r) (NOTE: the work done is path independent)

Electric Potential Energy (Ee)

energy that a charge has due to its position in an electric field

Electric Potential Difference (ΔV)

electric potential energy difference per unit charge between two points in an electric field (ΔV \= ΔEe / q OR ΔV \= W / q)

Electronvolt (eV)

energy gained by an electron moving through an electric potential difference of one volt. (OR: Work done moving an electron through an electric potential difference of one volt.) (1 eV \= 1.60 x 10-19 J)

Electric Current (I)

current is defined in terms of the force per unit length between parallel current-carrying conductors (NOTE: one ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per unit length of 2 x 10-7 newtons)

Resistance (R)

ratio of potential difference applied to a device to the current through the device (R \= V/I)

Ohm's Law - The current flowing through a device is proportional to the potential difference applied across it providing the temperature is constant. (NOTE: R \= V/I is not a statement of Ohm's Law)

Electromotive Force (emf) (ε)

Total energy difference per unit charge around a circuit (total energy per unit charge made available by the chemical reaction in the battery) (ε \= ΔEe/q OR ε \= W/q)

Magnitude of a Magnetic Field (magnetic field strength, magnetic field intensity, magnetic flux density) (B)

ratio of magnetic force on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic field (B \= FB / Ilsinθ)

Direction of a Magnetic Field

the direction that the North pole of a small test compass would point if placed in the field (N to S)

Magnetic Flux (Φ)

product of the magnetic field strength and a cross-sectional area and the cosine of the angle between the magnetic field and the normal to the area (Φ \= B A cosθ)

Magnetic Flux Linkage

product of the magnetic flux through a single coil and the total number of coils (flux linkage \= N Φ)

Faraday's Law

The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage. (ε α N ΔΦ/Δt)

Lenz's Law

The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic field that produced it. (NOTE: This is the negative sign added to Faraday's law. ε\= - N ΔΦ/Δt)

Nuclide

a particular type of nucleus with a certain number of protons and neutrons

Isotope

nuclei with the same number of protons (Z) but different number of neutrons (N)

Nucleon

a proton or neutron (NOTE: Do not say "a particle in the nucleus" since that would include quarks as well.)

Nucleon Number (Mass Number) (A)

number of nucleons (protons + neutrons) in nucleus

Proton Number (Atomic Number) (Z)

number of protons in nucleus

Neutron Number (N)

number of neutrons in nucleus (N \= A - Z)

Radioactive Half-life (T1/2)

the time taken for ½ the number of radioactive nuclei in sample to decay

Unified Atomic Mass Unit

1/12th the mass of a carbon-12 nucleus

Mass Defect

difference between the mass of the nucleus and the sum of the masses of its individual nucleons

Binding Energy

energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is separated into its individual components)

Binding Energy per Nucleon

energy released per nucleon when a nuclide is assembled from its individual components (OR: energy required per nucleon when nucleus is separated into its individual components)

Nuclear Fission

a heavy nucleus splits into two smaller nuclei of roughly equal mass

Nuclear Fusion

two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun's energy.)

Photoelectric Effect

the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface

de Broglie Hypothesis

All particles can behave like waves whose wavelength is given by λ \= h/p where h is Planck's constant and p is the momentum of the particle.

Matter Waves

All moving particles have a "matter wave" associated with them whose wavelength is the de Broglie wavelength.

Radioactive Decay Law

The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei present in the sample at any one time. (A \= λN)

Decay Constant (λ)

constant of proportionality between the decay rate (activity) and the number of radioactive nuclei present

Energy Density (of a fuel)

the ratio of the energy released from the fuel to the mass of the fuel consumed

Albedo (α)

fraction of the total incoming solar radiation received by a planet that is reflected back out into space (OR: ration of total solar radiation power scattered by a planet to total solar radiation received by a planet) (NOTE: global annual mean albedo is 0.3 for Earth)

Surface Heat Capacity (CS)

energy required to raise the temperature of a unit area of a planet's surface by 1 K. (CS \= Q / (A ΔT))

Coefficient of Volume Expansion (γ)

fractional change in volume per degree change in temperature (γ \= ΔV / (V0 ΔT))

Capacitance (C)

ratio of charge stored in a device to the potential difference across the device (C \= q / V)

Quantum Efficiency (of a pixel)

ratio of the number of photoelectrons emitted to the number of photons incident on the pixel