IB PHYSICS SL DEFINITIONS Topic 1: Physics and Physical Measurement 1.2.6b) systematic error Error that is identical for each reading / error caused by zero error in instrument / OWTTE; Topic 2: Mechanics 2.1.2a) average speed, instantaneous speed, and difference between them Average speed: speed over a period of time/distance / distance travelled divided by time taken; Whereas instantaneous speed is speed/rate of change of distance at a particular instant in time/point in space; 2.2.8b) Newton s second law of motion related to momentum The rate of change of momentum of a body is equal/directly proportional to the net external force acting on the body; 2.2.14 Newton s third law of motion If object A exerts a force on object B, then object B (simultaneously) exerts an equal and opposite force on object A / OWTTE; 2.2.10a) linear momentum Product of mass and velocity; 2.2.10b) impulse Product of force and change in the time for which the force acts / change in momentum; 2.2.12 law of conservation of linear momentum If the net external force acting on a system is zero; Then the momentum of the system remains constant/unchanged/the same; Or For a closed system; The momentum remains constant/unchanged/the same; 2.3.9 power Rate of working / work divided by time;
Topic 3: Thermal Physics 3.1.1 corollary thermal equilibrium When the rate of energy absorption is equal to the rate of energy emission / temperature of substance remains constant; 3.1.3 internal energy Total random kinetic and potential energy of a substance s molecules; 3.1.4c) thermal energy (heat) (Net) amount of energy transferred between a system and its surroundings / two bodies at different temperatures; 3.1.5a) mole Molecular weight of a substance in grams / 6.0 x 10 23 atoms/molecules/particles (depending on context of question) / same number of particles as in 12 g of C-12 / the amount of a substance that contains as many elementary entities as the number of atoms in 12 g of the isotope carbon-12; 3.1.5b) molar mass The mass of one mole of a substance; 3.2.1a) specific heat capacity The energy required to change the temperature of a substance by 1K/ C/unit degree; Of mass 1 kg / per unit mass; 3.2.1b) thermal capacity (Thermal) energy/heat required to change temperature of a substance by 1K// C/unit degree / mass x specific heat capacity; 3.2.10 assumptions of the kinetic model of an ideal gas Point molecules / negligible volume; No forces between molecules except during contact; Motion/distribution is random; Elastic collisions /no energy lost; Obey Newton s laws of motion; Collision in zero time; Gravity is negligible/ignored;
Topic 4: Oscillations and Waves 4.1.2b) amplitude The maximum displacement of the system from equilibrium/center of motion / OWTTE; 4.1.3 simple harmonic motion (SHM) The acceleration of the body is proportional to its displacement from equilibrium; And directed towards equilibrium; 4.3.1 damping The amplitude of the oscillations / (total) energy decreases (with time); Because a force always opposes direction of motion / there is a resistive/friction force; *cannot just say friction force for marks 4.3.5 resonance When driving frequency is equal/close to natural frequency; 4.4.1b) continuous progressive/travelling wave Transfer of energy by means of oscillations/vibrations; 4.4.3a) transverse wave Energy of the wave is propagated at right angles to the direction of oscillation of the wave s particles; 4.4.3b) longitudinal wave Vibrations all in one direction parallel to direction of energy transfer; 4.4.4 ray, wavefront, and relationship between them Ray: direction of wave travel / energy propagation; Wavefront: line that joins points with same phase/of same crest/trough/displacement; Relationship between ray & wavefront: ray normal/perpendicular/at right angles to wavefront; 4.4.9b) electromagnetic waves orders of magnitude Radio: > 10 cm Microwave: 1 cm Infrared: 750 nm 10-4 m Visible light: ~600 nm; ~400-700 nm Ultraviolet: 5 x 10-8 m
X-ray: 10 pm 1 nm Gamma: < 10 pm 4.5.5a) principle of superposition of waves If two or more waves meet/overlap/pass through the same point; Then the resultant displacement at any point is the (vector) sum of the individual displacements; Topic 5: Electric Currents 5.1.5 electric current/ampere Force per unit length between parallel current-carrying conductors *NOT the number of electrons passing through a point in a given time!! 5.1.6 resistance Ratio of potential difference across a device to the current in/through it; 5.1.8 Ohm s law The resistance of a conductor is constant provided its temperature is constant / the current is proportional to the voltage across; 5.2.1 electromotive force (emf) Power (*NOT energy!!) supplied by the cell per unit current from the cell / energy supplied per unit charge / work done per unit charge 5.2.2 internal resistance Some of the power/energy delivered by a cell is used/dissipated in driving the current through the cell itself; The power loss can be equated to I 2 r, where r is the internal resistance of the cell; Topic 6: Fields and Forces 6.1.1 Newton s universal law of gravitation The attractive force between two point masses; Is proportional to the product of their masses and inversely proportional to the square of the distance apart; 6.1.2 gravitational field strength The attractive force exerted per unit mass;
On a point (small) mass; 6.2.4 Coulomb s law The force between two point charges; Is inversely proportional to the square of their separation and directly proportional to (the product of) their magnitudes; *full marks also allowed for an equation involving F, Q, and r as long as symbols are defined 6.2.5 electric field strength The force exerted per unit charge; On a positive small/test charge; Topic 7: Atomic & Nuclear Physics 7.1.2 evidence supporting nuclear model of the atom Rutherford s experiment: Most alpha particles used to bombard a thin gold foil pass through the foil without a significant change in direction. A few alpha particles are deviated from their original direction through angles greater than 90. Rutherford s model: o Most of the atom is empty space; o Most of the mass/(protonic) charge of the atom is concentrated in the nucleus / the nucleus is dense; o Nucleus is positively charged; o Most of the alphas are not close enough to nuclei to be deflected; o Very few alphas are close enough to nuclei to be deflected; 7.1.5a) nuclide A species of atom that is characterized by the constitution of its nucleus / the number of protons and neutrons in the nucleus OWTTE; 7.1.5b) isotope Same proton number/element/same number of protons AND different number of neutrons/nucleon number/neutron number; (both parts needed for the point) 7.1.6a) nucleon number Total number of protons and neutrons in an atom;
7.2.7 half-life Time for the activity (of a radioactive sample) to fall by half its original value / time for half the radioactive/unstable nuclei/atoms (in a sample) to decay; 7.3.3 unified atomic mass unit 1/12 th the mass of an atom of Carbon-12; 7.3.5b) binding energy of a nucleus The (minimum) energy required to (completely) separate the nucleons in a nucleus / the energy released when a nucleus is assembled from its constituent nucleons; 7.3.8a) nuclear fission The process by which a heavy nucleus splits into two lighter nuclei; 7.3.8b) nuclear fusion The process of joining together two small nuclei to form a larger nucleus; Topic 8 8.1.2 degraded energy Energy transferred to surroundings from system / energy converted to thermal energy; Energy no longer available for performance of useful work / cannot be used again; *cannot simply say lost energy 8.2.3 energy density Energy released per unit mass/volume / per kg/m 3 *NOT per unit density!! 8.4.1 corollary critical mass Amount of fissile material that will allow fission to be sustained; *NOT the minimum mass necessary for fission to take place, NOR the amount of fissile material that will allow a growing chain reaction to take place!! 8.4.3 fuel enrichment The amount of uranium-235 present in the fuel is increased / OWTTE; 8.5.2 albedo Fraction of energy/power incident in a surface that is reflected / OWTTE; 8.5.4 greenhouse effect Greenhouse gases absorb infrared radiated by Earth s surface;
The part of the radiation that is re-radiated back to Earth will cause the surface temperature to rise / be re-radiated at a different frequency / OWTTE; 8.5.10a) Stefan-Boltzmann law for black bodies Energy emitted per unit time / power emitted per unit area; Proportional to [absolute temperature/temperature in K] 4 8.5.11 emissivity Ratio of energy/power emitted (per unit area) of a body; To the energy/power emitted (per unit area) of a black body of the same dimensions at the same temperature; Or Ratio of power emitted by a body; To the power emitted if it were a black body; 8.6.2 enhanced greenhouse effect Increased infrared radiation from the atmosphere to Earth / OWTTE / increase in the greenhouse effect due to human activity; Other Equilibrium To be in translational equilibrium: All forces on object must cancel out / net force = 0 / resultant force on the body in ANY direction is 0 So for example, something traveling in a circle is NOT in equilibrium o Changing direction o Has acceleration o Forces can never cancel out if something is traveling in a circle o Etc. Field of force Region/area/volume (of space); Where a mass/charge experiences a force; Fuel Source of energy in a useful form;
Greenhouse gases Infrared radiation radiated from Earth will be absorbed by greenhouse gases; And so increase the temperature of the atmosphere/earth;