HL Physics

absolute uncertainty

a quantity giving the extremes a measured value falls within

absolute zero

the temperature at which all random motion of molecules stops

absorption spectra

the set of wavelengths of photons absorbed by a substance

acceleration of free fall

the acceleration due to the pull of the Earth on a body

accurate

a measurement where the systematic error is small and so close to the "true" value

activity

the rate of decay of a radioactive sample

albedo

the ration of scattered to incident intensity of radiation

alpha particle

the nucleus of helium-4

alternating current (ac)

current in which electrons oscillate instead of moving with the same drift speed in the same direction

Amonton's law or Gay-Lussac's law

the relation between pressure and temperature of a fixed quantity of an ideal gas when the volume is kept constant

amplitude

the largest value of the displacement from equilibrium of an oscillation

angular frequency or angular speed

the ratio of angle turned to time taken

angular momentum

the product of mass, speed and orbit radius of a particle

angular separation

the angle that the distance between two objects subtends at the observer's eye

antinode

a point in a medium with a standing wave where the displacement is momentarily a maximum

anti-particle

a particle with the same mass as its particle but with all other properties opposite, such as electric charge

atomic (or proton) number

the number of protons in a nucleus

atomic mass unit

a unit of mass equal to 1/12 the mass of a neutral atom of carbon-12

average speed

the ratio of distance travelled to total time taken

average velocity

the ratio of displacement to total time taken

Avogadro constant

the number of particles in one mole

baryon

a particle made up of three quarks

baryon number

a conserved quantum number; it is assigned to each quark, and by extension to baryons

beta minus decay

a decay producing an electron and an anti-neutrino

beta plus decay

a decay producing a positron and a neutrino

binding energy

the minimum energy that must be supplied to completely separate the nucleons in a nucleus or the energy released when a nucleus is assembled

black body

a theoretical body that reflects none of the radiation incident on it and so absorbs all of it

blue-shift

a decrease in the observed wavelength

boiling

the change from the liquid to the vapour state at a specific constant temperature

Boyle's law

the relation between pressure and volume of a fixed quantity of an ideal gas when temperature is kept constant

capacitance

the charge that can be stored on a capacitor per unit voltage

centripetal acceleration

the acceleration due to a changing direction of velocity

centripetal force

a force pointing to the centre of a circular path

chain reaction

a self-sustaining reaction

charge carrier

charged particles that are able to move, creating an electric current

Charles' law

the relation between volume and temperature of a fixed quantity of an ideal gas when the pressure is kept constant

coefficient of dynamic friction

the ratio of the force of friction to the normal reaction force on a body while the body is sliding on a surface

coefficient of static friction

the ratio of the maximum force of friction that can develop between two bodies to the normal reaction force on a body while the body is at rest

coherent

sources whose phase difference is constant in time

compression

a point in a medium through which a wave is travelling that has maximum density

condensation

the change from the vapour to the liquid state

conduction

the transfer of heat through electron and molecular collisions

conservation of energy

the principle that energy cannot be destroyed or created but can only be changed from one form into another

conservation of momentum

when the net force on a system is zero, the total momentum of the system is constant

conserved

a quantity that states the same before and after an interaction

constructive interference

the superposition of two identical waves that arrive at a point in phase

control rod

a rod that regulates the the rate of energy release in a nuclear fission reactor by regulating the absorption of neutrons

convection current

motion of a fluid as a result of differences in fluid density

convection

the transfer of heat in fluids through differences in fluid density

Coulomb's law

the electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation

crest

a point on a wave of maximum displacement

critical angle

the angle of incidence for which the angle of refraction is a right angle

critical mass

the smallest mass of fissionable material that can sustain fission reactions

decay constant

the probability per unit time for a nucleus to decay

destructive interference

the superposition of two identical waves that arrive at a point 180 degrees out of phase

diffraction

the spreading of a wave past an aperture or an obstacle

diffraction grating

a series of very many and very narrow slits

diode

a device that lets current through it only in one direction

diode bridge rectifier

a circuit that achieved full-wave rectification

dipole

a pair of two equal and opposite electric charges

direct current (dc)

current in which electrons move in the same direction with the same average drift speed

discrete

energy that can take a set of specific values as opposed to a continuous range of values

dispersion

the dependence of refractive index on wavelength

displacement

the change in position; for an oscillation, the distance between the position of a particle and its equilibrium position

Doppler effect

the change in measured frequency when there is relative motion between source and observer

drag force

a force of resistance to motion

eddy currents

small induced currents in a conductor where the flux is changing that dissipate energy

efficiency

the ratio of useful work or power to input work or power

elastic potential energy

the energy stored in a spring when it is compressed or stretched

electric field strength

the electric force per unit charge experienced by a small point positive charge

electric potential

the work done per unit charge by and external agent in bringing a small point positive charge from infinity to a point

electric potential energy

the work that needs to be done by and external agent in order to bring a set of charges from where they were separated by an infinite distance to their current position

electric resistance

the ratio of the voltage across a device to the current through it

electromagnetic

an interaction mediated by the exchange of photons

electromagnetic waves

transverse waves moving at the speed of light in vacuum consisting of oscillating electric and magnetic fields at right angles to each other

electroweak interaction

the interaction that is the unification of the electromagnetic and weak nuclear interactions

elementary particles

particles that have no constituents

emf

the work done per unit charge in moving charge across the terminals of a battery

emission spectrum

the set of wavelengths of photons radiated by a substance

emissivity

the ratio of the intensity radiated by a body to the intensity radiated by a black body of the same temperature

energy density

the energy that can be obtained from a unit volume of fuel

equation of state

the equation relating pressure, volume, temperature and number of moles of a gas

equilibrium

the state when the net force on a system is zero

equipotential surfaces

set of points that have the same potential

escape velocity

the minimum speed at launch so that a particle can move to infinity and never return

exchange particle

an elementary particle used as the intermediary of an interaction

excited state

a state of energy higher than the ground state

family lepton number

a quantum number assigned to each lepton in each family

Faraday's law

the induced emf in a loop is the rate of change of magnetic flux linkage through the loop

Feynman diagram

a pictorial representation of an interaction

first harmonic

the mode of vibration of a standing wave of lowest frequency

flux linkage

the magnetic flux in a loop times the number of turns in the loop

force pair

two forces acting on different bodies that are equal and opposite according to Newton's third law

fractional uncertainty

the ratio of the absolute uncertainty to the mean value of a quantity

free-body diagram

a diagram showing a body in isolation with all forces acting on it drawn as arrows

freezing

the change from the liquid to the solid state at a specific constant temperature

frequency

the number of full oscillations or waves in unit time

fuel rods

containers of nuclear fuels in a nuclear fission reactor

full-wave recitification

the turning of ac current into dc current during both halves of the cycle

gamma ray

a photon