Lower Saxony Zentralabitur Physics key terms

Motion in which velocity stays constant, so equal distances are covered in equal time intervals and acceleration is zero. Position changes linearly with time and the acceleration-time graph lies on the axis.

Rate at which velocity changes with time, measured in metres per second squared. It is positive when speed increases in the direction of motion and negative when the motion slows down.

Graph of velocity against time. Its slope equals acceleration and the area between the curve and the time axis equals the distance travelled, which makes it a standard tool for evaluating motion experiments.

A vector quantity that changes the state of motion or deforms a body, measured in newtons. Several forces acting on one body are combined by vector addition into a single resultant force.

The resultant force on a body equals the product of its mass and its acceleration, written F = m·a. It links the cause of motion to the change of motion and holds only in inertial frames.

The property of a body to resist changes to its state of motion, expressed by its inertial mass. A larger mass needs a larger force for the same acceleration and keeps its velocity when no resultant force acts.

Vector product of mass and velocity, measured in kilogram metres per second. In a closed system the total momentum stays constant, which makes it the key quantity for analysing collisions and explosions.

Principle stating that the total momentum of a closed system does not change over time because internal forces cancel in pairs. It allows unknown velocities after collisions to be calculated without knowing the forces involved.

Principle that energy can be transformed but never created or destroyed, so the total energy of a closed system remains constant. It connects kinetic, potential, thermal and electrical forms in one balance equation.

Energy a body possesses because of its motion, calculated as one half of mass times velocity squared. It grows quadratically with speed and is always non-negative, so reversing direction does not change it.

Stored energy that depends on the position of a body in a force field, such as height in a gravitational field or charge near another charge. Only differences of potential energy have physical meaning.

Newton's law stating that two masses attract each other with a force proportional to the product of the masses and inversely proportional to the square of their distance. The constant of proportionality is the gravitational constant.

The net force directed towards the centre of a circular path that keeps a body on that path, equal to mass times speed squared divided by radius. It is provided by gravity, tension, friction or magnetic forces.

Motion along a circular path at constant speed, in which the velocity direction changes continuously while the speed stays the same. The resulting centripetal acceleration points towards the centre of the circle.

Law describing the force between two point charges: proportional to the product of the charges and inversely proportional to the square of their separation. The force acts along the connecting line and can attract or repel.

Vector quantity giving the force per unit positive charge at a point in an electric field, measured in volts per metre or newtons per coulomb. Field lines point away from positive and towards negative charges.

Difference in electric potential energy per unit charge between two points, measured in volts. It drives current through a conductor and equals the work per charge that the field can perform.

For an ohmic conductor at constant temperature, current is proportional to applied voltage, so resistance is constant. The relation U = R·I fails for components such as lamps and diodes whose resistance changes.

Quotient of voltage across a component and current through it, measured in ohms. It quantifies how strongly a component opposes current and depends on material, length, cross-section and temperature.

Two conservation statements for circuits: the sum of currents at a junction is zero, and the sum of voltages around any closed loop is zero. They follow from charge and energy conservation.

Vector quantity describing the strength and direction of a magnetic field, measured in tesla. It determines the force on moving charges and current-carrying conductors and the flux through a surface.

Force on a moving charge in a magnetic field, proportional to charge, speed, flux density and the sine of the angle between velocity and field. It acts perpendicular to both velocity and field.

Product of magnetic flux density and the area perpendicular to it, measured in webers. A change in flux through a circuit, caused by changing field, area or orientation, is the origin of induced voltage.

Generation of a voltage in a circuit by a changing magnetic flux through it. The induced current opposes the change that produced it, and the magnitude of the voltage is proportional to the rate of flux change.

Statement that an induced current flows in the direction whose magnetic field opposes the flux change causing it. It expresses energy conservation and explains the braking effect observed in induction experiments.

Oscillation in which the restoring force is proportional to displacement and directed towards equilibrium. Displacement follows a sine or cosine function with constant amplitude and frequency, independent of amplitude.

Mass attached to a spring, oscillating with angular frequency equal to the square root of spring constant divided by mass. Its period is independent of amplitude and depends only on mass and stiffness.

Strong increase of oscillation amplitude when a system is driven near its natural frequency. Damping limits the maximum amplitude and shifts the resonance peak to a slightly lower frequency.

Distance between two neighbouring points in a wave that are in the same phase, such as two crests. It relates to frequency and wave speed through the wave equation and sets the scale for interference patterns.

Superposition of two or more waves, producing amplification where they arrive in phase and cancellation where they arrive in antiphase. The resulting pattern depends on path difference and wavelength.

Spreading of a wave after passing an obstacle or opening, becoming noticeable when the opening is comparable to the wavelength. It makes interference patterns behind slits and gratings possible.

Emission of electrons from a metal surface illuminated by light above a threshold frequency. The maximum kinetic energy of the electrons depends on frequency, not intensity, which supports the photon model.

Quantum of electromagnetic radiation carrying energy proportional to frequency through Planck's constant. Photons have no rest mass and move at the speed of light in vacuum.

Minimum energy needed to remove an electron from a metal surface, characteristic of the material. In the photoelectric effect it equals the photon energy minus the maximum kinetic energy of emitted electrons.

Concept that quantum objects show both wave and particle properties depending on the experiment. Interference reveals wave behaviour, while localised detection events reveal particle behaviour.

Wavelength assigned to a particle, equal to Planck's constant divided by its momentum. It explains electron diffraction and becomes negligibly small for macroscopic objects.

Model in which electrons occupy discrete circular orbits around the nucleus and emit or absorb photons only when changing orbit. It explains atomic line spectra but fails for multi-electron atoms.

One of the discrete allowed energy values of a quantum system such as an atom. Transitions between levels produce or absorb photons whose energy equals the difference between the levels.

Spontaneous transformation of unstable nuclei into other nuclei, accompanied by emission of alpha or beta particles or gamma radiation. It is a random process for single nuclei but follows statistical decay laws.

Time after which half of the radioactive nuclei present in a sample have decayed. It is characteristic of the nuclide and leads to an exponential decrease of the number of undecayed nuclei.

Number of decays per unit time in a radioactive sample, measured in becquerel. It decreases exponentially with the same half-life as the number of undecayed nuclei.

Difference between the mass of a nucleus and the sum of the masses of its separate nucleons. It corresponds to the binding energy through the mass-energy relation and explains energy release in nuclear reactions.

Splitting of a heavy nucleus into lighter fragments after absorbing a neutron, releasing energy and further neutrons. The released energy comes from the higher binding energy per nucleon of the fragments.

Energy required to separate a nucleus completely into its individual protons and neutrons. Per nucleon it peaks near iron, so fusion of light nuclei and fission of heavy nuclei both release energy.

Model in which particles have negligible volume and interact only through elastic collisions. Pressure, volume and temperature are linked by the ideal gas law, and internal energy depends only on temperature.

Energy conservation for thermodynamic systems: the change in internal energy equals heat supplied plus work done on the system. Sign conventions must be stated clearly when applying it.

State quantity measuring how many microscopic arrangements correspond to a macroscopic state, often described as a measure of disorder. It increases in irreversible processes in isolated systems and never decreases there.

Relativistic effect in which a clock moving relative to an observer runs slower, by the Lorentz factor. It is symmetric between inertial frames and has been confirmed with muons and atomic clocks.

Dimensionless factor depending on relative speed, equal to one at rest and growing without limit as speed approaches the speed of light. It scales time dilation, length contraction and relativistic momentum.

Shortening of an object measured in a frame in which it moves along its length, by the Lorentz factor. The effect applies only to the direction of motion and is not observed in the object's rest frame.

Quantified range within which the true value of a measured quantity is expected to lie, combining random and systematic contributions. It is estimated from instrument resolution, repeated readings and calibration information.

Method for calculating the uncertainty of a result from the uncertainties of the measured quantities used to compute it. Absolute uncertainties are combined in quadrature when contributions are independent and random.

Number of meaningful digits in a reported value, indicating the precision of the measurement behind it. Results should be rounded consistently with the uncertainty and not overstate precision.