# Physics- General Definitions.txt

 Displacement Position of an object relative to its starting position. Velocity Rate of change of displacement. Speed Rate of change of distance. Acceleration Rate of change of velocity.Newton's First LawAn object continues in uniform motion in a straight line/ at rest unless a resultant force acts. Newton's Second Law The acceleration of an object is proportional to and in the same direction as its resultant force. Newton's Third Law When 2 objects react, the exert equal and opposite forces on each other. Linear Momentum The product of mass and velocity. Impulse Change in momentum. Law of conservation of momentum Momentum of object in system stays the same in a closed system. Work Force X distance moved in direction of force. Kinetic Energy The energy an object has due to it's motion Change in GPE The energy an object has due to its position above the Earth.Elastic CollisionKE is conserved and objects bounce off with the same speed it did before in opposite directions. Inelastic Collision Maximum loss of KE, objects stick together & momentum is still conserved. Explosion Objects move away from each other, internal energy becomes KE. Efficiency Ratio of work out: energy put in. Mole Amount of substance that has the same number of molecules as the number of of molecules as the number of atoms in 12g of C-12. Molar Mass Mass of 1 mole of the substance. Avogadro's Constant Number of molecules in 1 mole = 6.022 × 10²³ Specific Heat Capacity The energy needed to increase the temperature of of 1 kilo of an object by 1K. Thermal Capacity The energy needed to increase the temperature of an object by 1K. Specific Latent Heat Amount of heat needed to change the state of 1 kilo of a substance WITHOUT a change in temperature. Pressure Force per unit area. Displacement (SHM) Distance away a particle is from its equilibrium position. Amplitude (SHM) Maximum displacement of a particle from its equilibrium position. Frequency (SHM) Number of oscillations produced per second. Period (SHM) Time taken for a complete oscillation. Phase Difference (SHM) The fraction of an oscillation that one wave moves behind another. Simple Harmonic Motion Motion where the acceleration of an object is proportional to & in the opposite direction to displacement. a = -ω2x Damping Process where the energy of an oscillating system decreases with amplitude by a dissipative force acting in the opposite direction. Natural frequency The frequency that a system naturally oscillates at. Forced oscillation An oscillation that occurs & stays , Where an object is forced to oscillate by an external force. Resonance When the frequency of a driving force matches the natural frequency of oscillation. Transverse wave Oscillations are at 90° to direction of energy transfer/ wave motion. Longitudinal wave Oscillations are parallel to direction of energy transfer/ wave motion. Crest Point on a wave with maximum positive displacement. Trough Point on a wave with maximum negative displacement. Compression Region (on a wave) where particles are closer together than they would be in their equilibrium state. Rarefaction Region (on a wave) where particles are further apart than they would be in their equilibrium state. Wavelength The shortest distance between 2 points on a wave that are in phase. Wave speed The speed at which wave fronts pass a stationary observer. Intensity The power per unit area received by an observer from a wave. Principle of superposition When 2 or more waves of the same type meet, the total displacement at a point on a wave is the displacements of the individual waves added at that point. Constructive/destructive interference Phase difference is 0/ out of phase& path difference is a whole 'n' of wavelength/ a fraction of it. Electric potential difference Work done per unit charge in moving a positive charge from one point in the (electric) field to another. Electronvolt The amount of energy an electron gains by moving through a potential difference of 1 volt. Electric current The rate of flow of electrical charge. Resistance The ratio of voltage across the material to the current flowing through it. Ohm's Law The current through a wire is proportional to the p.d. across it; as long as the temperature is constant. Electromotive force (emf) The power supplied by the supply per unit current. Internal resistance Resistance of a source (of power). Gravitational field strength The force per unit mass experienced by a small test mass placed in the field. Newton's universal law of gravitation Any point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to their separation². Electric field strength The force per unit charge experienced by a small test charge placed in the field. Magnetic field strength F=BILsinøDirection: 90° to field lines. Nuclide An atom with a particular nucleus configuration. Nucleon A proton or a neutron. Isotope An element with the same number of protons but a different number of neutrons. Radioactive half life The time taken for the total number of nuclei (of a radioactive substance) to halve. Unified atomic mass The mass of ½ of the nucleus of a C-12 isotope. Mass defect The difference in mass between a nucleus and its separate nucleons. Binding energy per nucleon The total binding energy for the nucleus divided by the total number of nucleons Binding energy The energy needed to break up a nucleus into its constituent nucleons. Degraded energy Energy transferred to surroundings that can no longer do useful work. Energy density The mean energy liberated per kg of a fuel. Fuel enrichment A process where you increase percentage of U-235 to make fission more likely. Moderator Slows down fast neutrons to increase the chance of more reactions. (So they don't pass through the nuclei) Control rod This absorbs neutrons to control chain reactions. Heat exchanger This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. The thermal energy is transferred to heat water, and the steam that is produced turns the turbines. Photovoltaic cell Light hits semiconductors & electrons are released/ moved; creating an electric field. Solar heating panel Heat goes through glass pane & is absorbed by black pipes with running water in them. Albedo The ratio of reflected: incident radiation. Stefan- Boltzmann law Total power radiated ∝ T⁴ OR P= σAT⁴. Emissivity The ratio of power emitted by a body to the power emitted if it was a black body. Surface heat capacity The energy needed to raise the temperature of a unit area of a planet's surface by 1K. Enhanced greenhouse effect Rising global temperatures due to greenhouse gases being put into the atmosphere because of human activities Coefficient of volume expansion The fractional change in volume per degree change in temperature. Gravitational potential Work done per unit mass in bringing a test mass from infinity to that point in the field. Gravitational potential energy Work done in moving an object from infinity to that point. Electric potential The work done per unit charge in bringing a positive test charge from infinity to that point in the field. Electric potential energy The work done moving a charge from infinity to a point in an electric field. Isochoric Constant volume: no work is done. Isobaric Constant pressure: Work done is area under line. Isothermal Constant temperature: Work done= area under curve. Adiabatic No heat transfer: compression/ expansion. Work is done on/ by gas Standing waves Transfer no energy. They have the same amplitude and are in phase. Happens when a wave & its reflection interfere (or just 2 waves) One dimensional standing wave Happens when a wave reflects back from a boundary along the route it came. Doppler Effect The change in perceived frequency because the source or observer is moving. Rayleigh criterion 2 points will be resolvable if the first minimum of the diffraction pattern of one source overlaps the central maximum of the diffraction pattern of the second source. Polarized light Light with waves that vibrate in 1 plane. Brewster's angle Happens when the transmitted ray is 90° to the reflected ray. The angle gives us the angle of incidence needed for plane-polarized light. Polariser A device that makes polarized light from an unpolarised beam. Analyser A polariser used to detect polarised light. Optically active substance A substance that rotates the plane of polarisation of light that goes through it. Stress analysis If polarised white light is shone on plastic, you can see the stress points where the coloured lines are. Magnetic flux A measure of the strength of a magnetic field over a given area/ number of field lines. Magnetic flux linkage The product of the magnetic flux and the number of turns in a given coil. Faraday's law The size of an induced emf is proportional to the rate of change of flux linkage. Lenz's law The direction of an induced current is such that it'll oppose the change causing it. de Broglie Hypothesis All particles have a wave like nature. Electron in a box model An electron has possible wavelengths like a standing wave on a string so electrons have discrete energies. Schrödinger's model This gives the probability of where the electron could be (probability regions called orbitals). Heisenberg uncertainty principle You can only know 1 from each pair:-momentum & position-energy & time Decay constant Probability of decay of a nucleus per unit time Radioactive decay law The activity of a radioactive sample ∝ Number of radioactive nuclei present. Capacitance Charge per unit p.d. that can be stored on a capacitor. Quantum efficiency The ratio of the number of photoelectrons emitted: the number of photons incident on the pixel. Magnification The ratio of the length of the image on the CCD: the length of the object. Stellar cluster A group of stars that are physically near each other in space. Constellation A pattern of stars as seen from Earth that aren't physically near each other in space. Light year The distance that light travels in 1 year. Luminosity The total power emitted by a star. Apparent brightness The power received per unit area on Earth by a star. Cepheid A slightly unstable star that has a regular variation in brightness and luminosity due to a periodic expansion and contraction in its outer layers. Red giant -Red-Comparatively cool-Large-Fuse elements other than Hydrogen Red Supergiant -Red-Large Mass-Large Surface Area-Large Luminosity-Low Surface Temperature White Dwarfs -Very Small/ Low Surface Area-Large Surface Temperature-White Visual Binary Stars can be distinguished using a telescope Spectroscopic Binary Analysis if its light spectrum shows 2 different classes of stars- the wavelengths show a periodic splitting in frequency. Eclipsing binary Analysis of the brightness of its light spectrum shows periodic dips. This is because on star is in the way of the other. Parsec A unit of distance that is equal to 3.26 light years Apparent magnitude How bright a star appears from Earth. Absolute magnitude The apparent magnitude a star would have if it was 10 parsecs away. Critical density The theoretical density of the universe that would create a flat universe. Hubble's Law The recessional velocity of a galaxy ∝ its distance away from Earth. Audible frequencies 2Hz - 20KHz (Sound) Intensity Amount of energy that a sound wave brings to a unit area every second. (Sound) Intensity Level 10 lg (I / I0);where I0 = 1.0 × 10-12 Wm-2. Attenuation Coefficient The probability of a single photon being absorbed in 1 m of the material- use defining equation. Half-value thickness The half-value thickness is that thickness of material which will reduce the intensity of the (transmitted) beam by 50% Acoustic Impedance The product of of the density of a substance and the speed of sound in that substance. Exposure The total ionized charge produced in unit mass of air by a particular radiation. Q=mX. Absorbed Dose The energy absorbed per unit mass of tissue. E=mD. Quality Factor This allows doses of different types of radiation to be compared for their biological effects. Dose Equivalent The amount of energy absorbed Physical Half-Life The time it takes for the activity of a sampleto halve. Biological Half-Life The time it takes the body to naturally eject half of an ingested sample of a radioactive isotope. AuthorAnonymous ID217755 Card SetPhysics- General Definitions.txt DescriptionGeneral Definitions of IB Physics Terms. Updated2013-05-05T05:23:07Z Show Answers