IB Physics Definitions

This took forever to make :/ all the terms taken from Tsokos IB Physics 7th Edition textbook

absolute zero

The temperature at which all random motion of molecules stops.

absorption spectrum

The set of wavelengths that can be absorbed.

acceleration

The rate of change of velocity; it is a vector.

acceleration of free fall

The acceleration, g, due to the pull of the earth on a body; g = 9.8 m s^-2 near the surface of the earth.

activity

The rate of decay (number of decays per second).

adiabatic

A thermodynamic process in which no heat enters or leaves the system.

albedo

The ratio of reflected to incident power or intensity; it has no unit.

alpha decay

A decay of a nucleus producing an alpha particle.

alternating current (ac)

Current which varies between positive and negative values.

alternating voltage

Voltage which varies between positive and negative values.

ammeter

An instrument that measures the electric current through it.

amplitude

The maximum displacement from equilibrium of a wave or oscillation.

angular acceleration

The rate of change of angular velocity; measured in rad s^-2.

angular displacement

The change in angular position; measured in rad.

angular impulse

The change in angular momentum.

angular position

The angle defining the position of a particle relative to some arbitrary reference line; measured in rad.

angular velocity (ω)

The rate of change of the angular position; measured in rad s^-1.

antinode

A point on a standing wave where the displacement is a maximum.

apparent brightness

The power received from a star per unit area (of the detector).

atmosphere

A non-SI unit of pressure.

atomic mass unit

1/12th of the mass of the neutral atom of carbon-12.

average speed

Total distance travelled divided by the time taken.

average velocity

Total displacement divided by total time.

Avogadro constant

The number of particles in one mole: 6.02214076 × 10^23.

background radiation

Radiation from natural sources such as cosmic rays and radioactive material in rocks.

beta minus decay

A decay of a nucleus producing an electron and an anti-neutrino.

beta plus decay

A decay of a nucleus producing a positron and a neutrino.

binding energy

The minimum energy required to separate/combine the nucleons of a nucleus, E_b = µc^2.

black body

A theoretical body that absorbs all the radiation incident on it and radiates the maximum possible intensity for a given temperature.

blue-shift

The shift in wavelength towards smaller wavelengths for an approaching source.

Boltzmann constant

The ratio of the gas constant to Avogadro’s number.

buoyant force

The force acting on an object in a fluid due to a difference in pressure at the top and bottom of the body; force is opposite to weight.

Carnot cycle

A thermodynamic cycle consisting of two isothermal and two adiabatic curves.

centripetal acceleration

The rate of change of velocity of a body in circular motion; directed towards the centre of the circle.

centripetal force

The force directed towards the centre of a circular path; F=mv^2/r.

chain reaction

A reaction in which the products are used to keep the reaction going.

Chandrasekhar limit

The maximum possible mass of a white dwarf, about 1.4 solar masses.

closed system

A system that can transfer energy, but not matter into or from its surroundings.

coefficient of dynamic friction

The ratio of the force of friction to the normal contact force on a body that is sliding along a surface.

coefficient of static friction

The ratio of the maximum force of friction between two bodies to the normal contact force when an object is at rest.

coherent sources

Sources with the same frequency and a constant phase difference between them.

compression

A point where the density of the medium is highest.

Compton scattering

The scattering of light off an electron.

condensation

When a vapour changes into a liquid.

conduction

Method of thermal energy transfer based on collisions of electrons with atoms.

conductors

Materials with many free electrons per unit volume, through which thermal energy and electric current can pass easily.

conservation of angular momentum

When the net torque on a system is zero, the angular momentum is conserved.

conservation of momentum

When the net force on a system is zero, the total momentum of the system remains constant.

conserved

A quantity that stays the same before and after an interaction.

constructive interference

Superposition of waves leading to maximum amplitude.

control rods

Rods that can easily absorb neutrons to control the rate of reactions.

convection

Method of thermal energy transfer due to the rising of lower density hot fluids.

convection currents

Motion of a fluid as a result of differences in fluid density.

Coulomb’s law

The force between two point charges is inversely proportional to the square of the separation and proportional to the product of the charges.

critical mass

The smallest mass of nuclear fuel that can sustain a chain reaction.

damping

The loss of energy of an oscillating system due to the presence of resistance forces.

daughter nucleus

The nucleus produced by radioactive decay.

decay constant

Probability of decay per unit time.

decay series

The series of decays until a nucleus reaches a stable nuclide.

destructive interference

Superposition of waves leading to zero (or minimum) amplitude.

diffraction

The spreading of a wave through an aperture or past an obstacle.

diffraction grating

A very large number of closely separated slits of negligibly small width.

direct current (dc)

Rate of flow of charge through the cross-sectional area of a conductor.

discrete energy

Energy taking a set of specific values rather than a continuous set of values.

displacement

Change in position; the difference between the position of the oscillating body and the position at equilibrium.

distance

Length of path followed.

Doppler effect

The change in observed frequency due to relative motion between the source and the observer.

drag force

The force acting against the motion of an object moving through a fluid.

driven oscillations

Oscillations when an external periodic force acts on the system.

driving frequency

The frequency of the external force acting on the system.

duality of matter

Matter has both particle and wave-like characteristics.

dynamic friction

A force opposing motion when a body moves.

efficiency, η

The ratio of useful work or power to input work or power.

Einstein’s postulates

1. All the laws of physics are the same in all inertial frames. 2. The speed of light in vacuum is the same for all inertial observers.

elastic collision

A collision in which the total kinetic energy before the collision equals the total kinetic energy after the collision.

elastic potential energy (E_H)

The energy stored in a spring that has been stretched or compressed; E_H = 1/2 kx^2.

electric charge

A conserved property of matter.

electric field

A region of space where an electric charge experiences an electric force.

electric field lines

Curves, tangents to which give the direction of the electric field strength.

electric field strength

The electric force per unit charge on a small positive point charge.

electric potential

The work done by an external agent per unit charge in bringing a small point positive charge from infinity to a point in an electric field.

electric potential energy

The work needed to bring a set of charges from infinite distance to their current position.

electric power

The energy per unit time dissipated in a conductor.

electrical resistance

The ratio of voltage across a conductor to current through it.

electromagnetic (EM) wave

A transverse wave moving at the speed of light in vacuum.

electromagnetic interaction

Force given by Coulomb’s law; acts on any particle that has an electric charge.

electromotive force (emf)

The work done per unit charge in moving charge across a battery’s terminals.

electroweak interaction

Represents the unification of the electromagnetic and weak nuclear interactions.

emission spectrum

The set of wavelengths of light emitted by an atom.

emissivity

The ratio of the intensity radiated by a body to that of a black body at the same temperature.

energy balance equation

An equation expressing the equality of incoming and outgoing intensities of radiation.

energy level diagram

A representation of the discrete energies of an atom.

enhanced greenhouse effect

The augmentation of the greenhouse effect due to human activities.

entropy

A measure of a system’s disorder.

equations of kinematics

suvat, check formula booklet A1.

equilibrium

The state when the net force on a system is zero.

equilibrium position

The position where an oscillator has no net force acting on it.

equipotential surfaces

Surfaces where all points are at the same potential.

escape speed

The minimum speed v_esc of an object in a gravitational field to reach infinity.

evaporation

Vaporisation taking place at the surface of a liquid at any temperature.