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Key Definitions for IB Physics HL Paper 2 2024 Exams

The required 251 Vocabulary – IB Higher Level Physics

As you delve into the IB Physics HL finals, particularly for Paper 2 and the upcoming 2024 exams, mastering a comprehensive array of concepts and principles is crucial. This guide is your ultimate resource, meticulously curated to bolster your exam preparation with essential definitions and explanations. Let's dive into the pivotal terms and concepts that are indispensable for your success.

Physics and Physical Measurement

1.  Fundamental Units – seven basic units of the SI measurement system: kilogram, second, mole, meter, ampere, Kelvin, candela.

2.  Derived Units – units that are combinations of fundamental units.  These combinations may or may not have a separate name. (eg. 1 kg m/s2 = 1 N)


3.     Accuracy -  An indication of how close a measurement is to the accepted value  (a measure of correctness).

4.     Precision -  An indication of the agreement among a number of measurements made in the same way (a measure of exactness).

5.   Random Uncertainty - An uncertainty produced by unknown and unpredictable variations in the experimental situation, such as temperature fluctuations and estimations when reading instruments.  (Affects the precision of results - Can be reduced by taking repeated trials but not eliminated – shows up as error bars on a graph)


6.     Systematic Error - An error associated with a particular instrument or experimental technique that causes the measured value to be off by the same amount each time. (Affects the accuracy of results - Can be eliminated by fixing source of error – shows up as non-zero y-intercept on a graph)


7.     Vector – a quantity with both a magnitude and a direction


8.     Scalar – a quantity with magnitude only




9.     *Displacement (s) - distance traveled in a particular direction (change in position)


10.  *Velocity (u,v) - rate of change of displacement


11.  *Speed (u,v) - rate of change of distance


12.  *Acceleration (a) - rate of change of velocity


13.  *Newton’s First Law of Motion – An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.


14.  *Newton’s Second Law of Motion – An unbalanced force will cause an object to accelerate in the direction of the net force.  The acceleration of the object is proportional to the net force and inversely proportional to its mass. (F­net = ma or Fnet = Δ p/Δ t (net force = rate of change of momentum))


15.  *Newton’s Third Law of Motion  - When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A.


16.  Translational Equilibrium  - net force acting on a body is zero


17.  *Linear Momentum (p) - product of mass and velocity


18.  *Impulse (J) - change in momentum


19.  *Law of Conservation of Linear Momentum - The total momentum of an isolated system (no external forces) remains constant.


20.  *Work (W) - The product of a force on an object and the displacement of the object in the direction of the force.


21.  Kinetic Energy (EK) – product of ½ times the mass of an object times the square of an object’s speed


22.  Change in Gravitational Potential Energy – product of an object’s mass times the gravitational field strength times the change in height


23.  *Principle of Conservation of Energy – The total energy of an isolated system (no external forces) remains constant.  (OR – Energy can be neither created nor destroyed but only transformed from one form to another or transferred from one object to another.)


24.  *Elastic Collision – a collision in which kinetic energy is conserved


25.  Inelastic Collision – a collision in which kinetic energy is not conserved


26.  *Power (P) - The rate at which work is done or the rate at which energy is transferred.


27.  *Efficiency (eff) - The ratio of the useful energy (or power or work) output to the total energy (or power or work) input.




28.  *Newton’s Universal Law of Gravitation – The force of gravity between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centers.  (NOTE: The objects are point masses.  If they are not point masses but are very far apart, that is, the distance between them is very much greater than their radii, they can be treated like point masses.)


29.  *Gravitational Field Strength (g) – gravitational force per unit mass on a point mass (g = Fg / m)


30.  *Gravitational Potential Energy (EP) - the work done in moving a mass from infinity to a point in space (NOTE: the work done is path independent)


31.  *Gravitational Potential (V) – the work done per unit mass in moving a mass from infinity to a point in space


32.  Equipotential Surface – every point on it has the same potential


33.  *Escape Speed – minimum speed of a rocket needed to escape the gravitational attraction of a planet


34.  *Kepler’s Third Law - the ratio of the orbital period squared to the average orbital radius cubed is constant for all planets


35.  Weightlessness in free-fall – a sensation of weightlessness because a person is falling freely toward the Earth, hence there is no normal force (reaction force) acting on the person due to gravity


36.  Weightlessness in orbital motion – a sensation of weightlessness due to the spacecraft and all objects in it being in constant free-fall together as they circle Earth


37.  Weightlessness in deep space – a sensation of weightlessness due to the minimal pull of gravity very far from any massive object


Thermal Physics


38.  *Temperature (T) –

a.          The property that determines the direction of thermal energy transfer between two objects.

b.         A measure of the average random kinetic energy of the particles of a substance.


39.  Thermal Equilibrium  - two objects are in thermal equilibrium when they are at the same temperature so that there is no transfer of thermal energy between them


40.  *Internal Energy of a substance (U) - The total potential energy and random kinetic energy of the molecules of the substance.


41.  *Thermal Energy (Heat) (Q) - Energy transferred between two substances in thermal contact due a temperature difference.


42.  *Mole - An amount of a substance that contains the same number of atoms as 0.012 kg of 12C.


43.  *Molar Mass - The mass of one mole of a substance.


44.  *Avogadro constant (NA) - The number of atoms in 0.012 kg of 12C ( = 6.02 x 1023).


45.  *Thermal Capacity (C) - energy required to raise the temperature of a substance by 1K


46.  *Specific Heat Capacity (c) - energy required per unit mass to raise the temperature of a substance by 1K


47.  Boiling – a phase change of a liquid into a gas that occurs at a fixed temperature


48.  Evaporation – when faster moving molecules have enough energy to escape from the surface of a liquid that is at a temperature less than its boiling point, leaving slower moving molecules behind which results in a cooling of the liquid


49.  *Specific Latent Heat (L) - energy per unit mass absorbed or released during a phase change


50.  *Pressure (P) – force per unit area acting on a surface


51.  *Ideal Gas - a gas that follows the ideal gas equation of state (PV = nRT) for all values of P, V, and T (an ideal gas cannot be liquefied)


52.  Real Gas – a gas that does not follow the ideal gas equation of state for all values of P, V, and T  (a real gas can approximate an ideal gas in some circumstances)


53.  Absolute Zero of Temperature – temperature at which a gas would exert no pressure


54.  Kelvin scale of Temperature – an absolute scale of temperature in which 0 K is the absolute zero of temperature


55.  *First Law of Thermodynamics (U = ΔU + W) – The thermal energy transferred to a system from its surroundings is equal to the work done by the system plus the change in internal energy of the system.  (an application of the principle of conservation of energy)


56.  Isochoric (Isovolumetric) – a process that occurs at constant volume (ΔV = 0)


57.  Isobaric – a process that occurs at constant pressure (ΔP = 0)


58.  Isothermal – a process that occurs at constant temperature (ΔT = 0)


59.  Adiabatic – a process that occurs without the exchange of thermal energy (Q = 0)


60.  *Entropy – a system property that expresses the degree of disorder in the system


61.  *Second Law of Thermodynamics – The overall entropy of the universe is increasing.  (OR – All natural processes increase the entropy of the universe.) (NOTE: The second law implies that thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temperature.)


Oscillations and Waves


62.  *Displacement (for waves) – distance a particle moves in a particular direction from its mean (equilibrium) position


63.  *Amplitude – maximum displacement from the mean position


64.  *Frequency (f) – number of oscillations per unit time


65.  *Period (T) – time taken for one complete oscillation (cycle) (OR: time taken for one cycle to pass a given point)


66.  *Phase Difference – difference in phase between two points


67.  *Simple Harmonic Motion – motion that takes place when the acceleration of an object is proportional to its displacement from its equilibrium position and is always directed toward its equilibrium position (NOTE: this motion is defined by the equation a = -ω2x)


68.  Damping – involves a force that is always in the opposite direction to the direction of motion of the oscillating particle (NOTE: this force is a dissipative force)


69.  Critical Damping – when a resistive force is applied to an oscillating system that causes the particle to return to zero displacement in a minimum amount of time


70.  Natural Frequency of Vibration – when a system is displaced from equilibrium and allowed to oscillate freely, it will do so at its natural frequency of vibration


71.  Forced Oscillations – a system may be forced to oscillate at any given frequency by an outside driving force that is applied to it


72.  *Resonance – a transfer of energy in which a system is subject to an oscillating force that matches the natural frequency of the system resulting in a large amplitude of vibration


73.  *Wave Pulse - single oscillation or disturbance in a medium


74.  *Continuous Progressive (Traveling) Wave – series of periodic pulses (NOTE: involves a transfer of energy)  (NOTE: each point on the wave has the same amplitude)


75.  *Transverse Wave – wave in which the direction of motion of the energy transfer (the wave) is perpendicular to the direction of motion of the particles of the medium (NOTE: light waves are transverse) (NOTE: transverse waves cannot be propagated in gases)


76.  *Longitudinal Wave – wave in which the direction of motion of the energy transfer (the wave) is parallel to the direction of motion of the particles of the medium (NOTE: sound waves are longitudinal)


77.  Wavefront - collection of neighboring points on a wave that are in phase


78.  Ray - line drawn perpendicular to a wavefront indicating the direction of motion of the energy transfer


79.  Crest - top of a transverse wave


80.  Trough - bottom of a transverse wave


81.  Compression - area of high pressure in a longitudinal wave


82.  Rarefaction - area of low pressure (expansion) in a longitudinal wave


83.  *Wavelength (λ) - shortest distance along the wave between two points in phase with one another  (OR: distance traveled by the wave in one period)


84.  *Wave Speed (v) - speed of transfer of the energy of the wave


85.  *Intensity (I) – power received per unit area (NOTE: for a wave, its intensity is proportional to the square of its amplitude)


86.  Law of Reflection - The angle of incidence is equal to the angle of reflection when both angles are measured with respect to the normal line


87.  *Snell’s Law - The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency.


88.  *Refractive Index (Index of Refraction) (n) –

a.  the ratio of the speed of the wave in the refracted medium to the speed of the wave in the incident medium


b.  the ratio of the sine of the angle of incidence to the sine of the angle of refraction


89.  Diffraction – the bending of a wave around an obstacle or the spreading of a wave through an opening (NOTE: diffraction is only noticeable when the size of the opening is smaller than or on the same order of the size of the wavelength)


90.  *Principle of Superposition – When two waves meet, the resultant displacement is the vector sum of the displacements of the component waves.


91.  Constructive Interference – superposition of two waves which are in phase with each other


92.  Destructive Interference - superposition of two waves which are out of phase with each other


93.  Path Difference – difference in the distances two waves must travel from their sources to a given point


94.  Standing (stationary) wave - resultant wave formed when two waves of equal amplitude and frequency traveling in opposite directions in the same medium interfere (NOTE: does not involve a transfer of energy) (NOTE: points on the wave have varying amplitudes)


95.  *Node - locations of constant complete destructive interference on a standing wave


96.  *Antinode - locations of maximum constructive interference on a standing wave


97.  Fundamental (First Harmonic) – lowest frequency mode of vibration of a standing wave


98.  *Doppler Effect - The change of frequency of a wave due to the movement of the source or the observer relative to the medium of wave transmission.


99.  Resolution – ability to distinguish between two sources of light


100.        *Rayleigh Criterion - When the central maximum of one diffraction pattern overlaps the first minimum of a second diffraction pattern, the two sources are “just resolved.”


101.        *Polarized Light – light in which the electric field vector vibrates in one plane only


102.        *Brewster’s Law – When light is incident on a surface at such an angle that the reflected and transmitted rays are perpendicular and the reflected ray is totally plane polarized, then the index of refraction of the substance is equal to the tangent of the angle of incidence. (n = tan θi)


103.        *Polarizer – device that produces plane polarized light from an unpolarized beam


104.        *Analyzer – polarizer used to detect polarized light


105.        Malus’ Law – the transmitted intensity of polarized light is equal to the product of the incident intensity times the square of the cosine of the angle between the direction of the analyzer and the direction of the electric field vibration of the polarized light (I = Io cos2 θ )


106.        Optically Active Substance – one that rotates the plane of polarization of the light that passes through it (OR: one that changes the plane in which the electric field vector of the light vibrates)




107.        *Law of Conservation of Charge – The total electric charge of an isolated system remains constant.


108.        Conductor – material through with electric charge flows freely


109.        Insulator – material through which electric charge does not flow freely


110.        *Coulomb’s Law – The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to square of the distance between them, and directed along the line joining the two charges.  (F = k q1 q2 / r2)


111.        Insulator – material through which electric charge does not flow freely


112.        *Electric Field Strength (E) - Electric force per positive unit test charge  (E = F/q)


113.        Radial Field – field that extends radially (like the electric field around a point charge or the gravitational field around a planet)


114.        *Electric Potential (V) - work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V = W/q)  (V = kq/r) (NOTE: the work done is path independent)


115.        *Electric Potential Energy (Ee)- energy that a charge has due to its position in an electric field


Electric Currents


116.        *Electric Potential Difference (ΔV) – electric potential energy difference per unit charge between two points in an electric field (ΔV = ΔEe / q   OR   ΔV = W / q)


117.        *Electronvolt (eV) – energy gained by an electron moving through an electric potential difference of one volt.  (OR: Work done moving an electron through an electric potential difference of one volt.)  (1 eV = 1.60 x 10-19 J)


118.        *Electric Current (I) –  current is defined in terms of the force per unit length between parallel current-carrying conductors (NOTE: one ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per unit length of 2 x 10-7 newtons)


119.        *Resistance (R) - ratio of potential difference applied to a device to the current through the device (R = V/I)


120.        Resistor - device with a constant resistance (Ohmic device) over a wide range of potential differences


121.        *Ohm’s Law – The current flowing through a device is proportional to the potential difference applied across it providing the temperature is constant.  (NOTE: R = V/I is not a statement of Ohm’s Law)


122.        Ohmic Device – one whose resistance remains constant over a wide range of potential differences (eg – resistor)


123.        Non-Ohmic Device – one whose resistance does not remain constant over a wide range of potential differences (eg – filament lamp)


124.        *Electromotive Force (emf) (ε) - Total energy difference per unit charge around a circuit  (total energy per unit charge made available by the chemical reaction in the battery) (ε = ΔEe/q    OR   ε = W/q)


125.        Internal Resistance (r) – resistance inside a battery that causes the battery’s terminal potential difference to be less than its emf (NOTE: internal resistance in a meter causes it not to act as an ideal meter)


126.        Ideal Ammeter – one with zero internal resistance – must be placed in series


127.        Ideal Voltmeter – one with infinite internal resistance – must be placed in parallel


128.        Potential Divider – two resistors placed in series that divide up the battery’s potential difference (R1 / R2 = V1 / V2)


129.        Light-Dependent Resistor (LDR) – sensor whose resistance depends on amount of light shining on its surface – increase in light causes a decrease in resistance


130.        Negative Temperature Coefficient (NTC) Thermistor  – sensor whose resistance depends on its temperature – increase in temperature causes decrease in resistance


131.        Strain Gauge – sensor whose output voltage depends on any small extension or compression that occurs which results in a change of length




132.        *Magnitude of a Magnetic Field (magnetic field strength, magnetic field intensity, magnetic flux density) (B) – ratio of magnetic force on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic field  (B = FB / Ilsinθ) (OR: ratio of magnetic force on a charged particle to the product of the charge and its velocity and the sine of the angle between the velocity and the magnetic field)  (B = FB / qvsinθ)


133.        *Direction of a Magnetic Field – the direction that the North pole of a small test compass would point if placed in the field  (N to S)


134.        *Magnetic Flux (Φ) - product of the magnetic field strength and a cross-sectional area and the cosine of the angle between the magnetic field and the normal to the area (Φ = B A cosθ)


135.        *Magnetic Flux Linkage – product of the magnetic flux through a single coil and the total number of coils (flux linkage = N Φ)


136.        *Faraday’s Law - The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage. (ε α  N ΔΦ/Δt)


137.        *Lenz’s Law - The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic field that produced it. (NOTE: This is the negative sign added to Faraday’s law.  ε= - N ΔΦ/Δt)


138.        Root Mean Square (rms) Value of an Alternating Current (or Voltage) – the value of the direct current (or voltage) that dissipates power in a resistor at the same rate (NOTE: The rms value is also known as the “rating.”)


Atomic and Nuclear Physics


139.        Geiger-Marsden experiment – also known as the Rutherford Alpha Particle Scattering or Gold Foil Experimet


140.        Photon – a discrete unit or package of light energy


141.        *Nuclide – a particular type of nucleus with a certain number of protons and neutrons


142.        *Isotope - nuclei with the same number of protons (Z) but different number of neutrons (N)


143.        *Nucleon – a proton or neutron (NOTE: Do not say “a particle in the nucleus” since that would include quarks as well.)


144.        *Nucleon Number (Mass Number) (A) - number of nucleons (protons + neutrons) in nucleus


145.        *Proton Number (Atomic Number) (Z) - number of protons in nucleus


146.        *Neutron Number (N) - number of neutrons in nucleus (N = A – Z)


147.        Coulomb interaction (Coulomb force, electrostatic force) – electrostatic force of repulsion between the protons in the nucleus


148.        Radioactive Decay – when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a random and a spontaneous process.) (NOTE: The rate of radioactive decay decreases exponentially with time.)


149.        Alpha Particle (α)– helium nucleus (2 protons + 2 neutrons)


150.        Beta Positive Particle (β+) – electron


151.        Beta Negative Particle (β-) – positron (antielectron)


152.        Gamma Radiation (γ) – high energy (high frequency) electromagnetic radiation


153.        *Radioactive Half-life (T1/2) – 

a.     the time taken for ½ the number of radioactive nuclei in sample to decay 

      b.     the time taken for the activity of a sample to decrease to ½ its initial value


154.        Artificial (Induced) Transmutation – when a nucleus is bombarded with a nucleon, an alpha particle or another small nucleus, resulting in a nuclide with a different proton number (a different element).


155.        *Unified Atomic Mass Unit – 1/12th the mass of a carbon-12 nucleus


156.        *Mass Defect – difference between the mass of the nucleus and the sum of the masses of its individual nucleons


157.        *Binding Energy – energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is separated into its individual components)


158.        *Binding Energy per Nucleon - energy released per nucleon when a nuclide is assembled from its individual components (OR: energy required per nucleon when nucleus is separated into its individual components)


159.        *Nuclear Fission - a heavy nucleus splits into two smaller nuclei of roughly equal mass


160.        *Nuclear Fusion - two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun’s energy.)


161.        *Photoelectric Effect - the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface

162.        Threshold Frequency (f0) - minimum frequency of light needed to eject electrons from a metal surface

163.        Work Function (Φ) - minimum energy needed to eject electrons from the surface of a metal

164.        Millikan’s Stopping Potential Experiment – an experiment utilizing reverse voltage raised to such a level (stopping potential Vs) that it stops all emitted photoelectrons (NOTE: This experiment is used to test the Einstein model of the explaining the photoelectric effect.)

165.        *de Broglie Hypothesis - All particles can behave like waves whose wavelength is given by λ = h/p where h is Planck’s constant and p is the momentum of the particle.

166.        *Matter Waves - All moving particles have a “matter wave” associated with them whose wavelength is the de Broglie wavelength.

167.        Wave-Particle Duality: Both matter and radiation have a dual nature.  They exhibit both particle and wave properties.

168.        Davisson-Germer Experiment – an experiment showing that electrons are scattered off crystals of nickel and interfere with each other – also know as “electron diffraction”  (NOTE: This experiment is evidence for the existence of matter waves.)

169.        Electron in a Box Model – a model of the atom useful for explaining the origin of atomic energy levels:  The model assumes that, if an electron is confined to move in one dimension by a box, the de Broglie waves associated with the electron will be standing waves of wavelength 2L/n where L is the length of the box and n is a positive integer.  Further, the kinetic energy of the electron in the box is n2h2/(8meL2)


170.        Schrödinger Model of the Atom – This model assumes that electrons in the atom may be described by wavefunctions.  The electron has an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electron at a particular point.

171.        Heisenberg Uncertainty Principle – Conjugate quantities (position-momentum or time-energy) cannot be known precisely at the same time.  (NOTE: There is a link between the uncertainty principle and the de Broglie hypothesis.  For example, if a particle has a uniquely defined de Broglie wavelength, then its momentum is known precisely but all knowledge of its position is lost.)

172.        Bainbridge Mass Spectrometer – a device used to determine atomic masses – consists primarily of a velocity selector and a magnetic chamber

173.        *Radioactive Decay Law – 


a.      The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei present in the sample at any one time. (A = λN)    

b.     N = N0e-λt  OR A = λ N0e-λt  (as an exponential function)

174.        *Decay Constant (λ) – 

              a.     constant of proportionality between the decay rate (activity) and the number of radioactive nuclei present    

            b.    probability of decay of a particular nuclei per unit time

175.        Activity (A) - number of radioactive disintegrations (decays) per unit time

Energy, Power and Climate Change

176.        Second Law of Thermodynamics – Thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.

177.        Degraded Energy – In any process that involves energy transformations, the energy that is transferred to the surroundings (thermal energy) is no longer available to perform useful work.

178.        Sankey Diagram – energy flow diagram

179.        Renewable Energy Source – source of energy that cannot be used up (eg. –hydroelectric, photovoltaic cells, active solar heaters, wind, biofuels) (NOTE: In most instances, the Sun is the primary energy source for world energy.)

180.        Non-renewable Energy Source – source of energy that can be used up (eg. – coal, oil, natural gas, nuclear)

181.        *Energy Density (of a fuel) – the ratio of the energy released from the fuel to the mass of the fuel consumed

182.        Fossil Fuels – coal, oil, and natural gas (NOTE: Industrialization led to a high rate of energy usage leading to industry being developed near large deposits of fossil fuels.)

183.        Chain Reaction – neutrons released from one fission reaction go on to initiate further reactions (NOTE: Only low-energy neutrons (≈ 1 eV) favor nuclear fission.)

184.        Critical Mass – minimum mass of radioactive fuel block needed for a chain reaction to occur

185.        Controlled Nuclear Fission – used for power production

186.        Uncontrolled Nuclear Fission – used for nuclear weapons

187.        Fuel Enrichment – process by which the percentage composition of a desirable radioactive nuclide (eg. – uranium-235) is increased in order to make nuclear fission more likely

188.        Moderator – Most neutrons released in fission are fast neutrons, so a moderator is used to reduce their energy down to thermal levels to ensure that the fission is self-sustaining. (eg. – may be made of solid graphite or steam)

189.        Control Rods – are used to remove any excess neutrons to ensure the fission reaction continues safely (eg. – may be made of cadmium or boron steel)

190.        Heat Exchanger – This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. Reactions increase temperature in the core and this thermal energy is transferred to water and the steam that is produced turns the turbines.

191.        Photovoltaic Cell (solar cell, photocell) – converts a portion of the solar radiation directly into a potential difference (voltage) using a semiconductor  (NOTE: A typical photovoltaic cell produces a very small voltage and is not able to provide much current so is usually used to run electrical devices that do not require a great deal of energy.)

192.        Active Solar Heater (solar panel) – designed to capture as much thermal energy as possible by allowing solar radiation to heat water running through a pipe in the panel.

193.        Oscillating Water Column (OWC) Ocean-Wave Energy Converter – device built on land that uses the kinetic energy of waves to force air in and out of a turbine which generates electrical energy

194.        *Albedo (α)– fraction of the total incoming solar radiation received by a planet that is reflected back out into space (OR: ration of total solar radiation power scattered by a planet to total solar radiation received by a planet) (NOTE: global annual mean albedo is 0.3 for Earth)

195.        Greenhouse Effect –Short wavelength radiation received from the Sun causes the Earth’s surface to warm up.  Earth will then emit longer wavelength radiation (infra-red) which is absorbed by some gases (eg. - methane, water vapor, carbon dioxide, nitrous oxide) in the atmosphere and re-radiated in all directions.  This extra warming of the Earth’s atmosphere is known as the Greenhouse Effect.

196.        Global Warming – increase in mean temperature of the Earth in recent years


197.        Enhanced (Anthropogenic) Greenhouse Effect – Human activities, mainly related to the burning of fossil fuels, have released extra carbon dioxide into the atmosphere, thereby enhancing or amplifying the greenhouse effect (a possible cause of global warming).


198.        Black-Body Radiation – radiation emitted by a “perfect” emitter of radiation

199.        Stefan-Boltzmann Law – The total power radiated by a black-body per unit area is proportional to the fourth power of the temperature of the body. (power = σAT4)

200.        Emissivity (ε) – ratio of power emitted by an object to the power emitted by a black-body at the same temperature.

201.        *Surface Heat Capacity (CS) – energy required to raise the temperature of a unit area of a planet’s surface by 1 K.  (CS = Q / (A ΔT))

202.        *Coefficient of Volume Expansion (γ) – fractional change in volume per degree change in temperature  (γ = ΔV / (V0 ΔT))

203.        Intergovernmental Panel on Climate Change (IPCC) – panel established by the World Meteorological Organization and the United Nations Environment Programme in 1988 in which hundreds of governmental scientific representatives from more than one hundred countries regularly assess the up-to-date evidence from international research into global warming and human induced climate change.

204.        Kyoto Protocol – an amendment to the United Nations Framework Convention on Climate Change in which signatory countries agree to work towards achieving a stipulate reduction in greenhouse gas emissions (NOTE: Notable non-signers are the United States and Australia.)

205.        Asia-Pacific Partnership on Clean Development and Climate (APPCDC) – agreement between six countries (representing approximately 50% of the worlds energy use – Australia, China, India, Japan, Republic of Korea, and USA) to “work together and with private sector partners to meet goals for energy security, national air pollution reduction, and climate change in ways that promote sustainable economic growth and poverty reduction.”

Digital Technology

206.        Decimal Number – number written using base-10

207.        Binary Number – number written using base-2

208.        Least-Significant Bit (LSB) – right hand digit representing the smallest power

209.        Most-Significant Bit (MSB) – left hand digit representing the largest power

210.        Bumps and Pits – high and low areas of a CD used to encode data (NOTE: Destructive interference occurs when light is reflected from the edge of a pit.)

211.        Analog – technique involving codes or signals that can take on a large number of different values between given limits – analog signals vary continuously with time

212.        Digital – technique involving codes or signals made up of a large number of binary digits (bits) that can each take only one of two possible values

213.        Bit – binary digit that can only take one of two possible values (1 or 0; ON or OFF; High or Low; True or False)

214.        Byte – eight separate bits of information

215.        *Capacitance (C) – ratio of charge stored in a device to the potential difference across the device (C = q / V)

216.        Charge-Coupled Device (CCD) – silicon ship divided into small areas called pixels (NOTE: CCDs are used for image capturing in a large range of the electromagnetic spectrum.  They are used in digital cameras, video cameras, medical X-ray imaging, and telescopes, such as the Hubble Telescope.)

217.        Pixel – small area of a CCD that acts as a capacitor

218.        *Quantum Efficiency (of a pixel) – ratio of the number of photoelectrons emitted to the number of photons incident on the pixel

219.        *Magnification – ratio of the length of the image on the CCD to the length of the object

OPTION H: Relativity

220.        Frame of Reference – the point of view of an observer or a coordinate system against which measurements are made consisting of x,y,z, axes and a clock

221.        *Galilean Transformation – equations that translate measurements made in one frame of reference to another frame of reference without taking into account the theory of relativity

222.        *Inertial Frame of Reference – a frame of reference that is not accelerating but is at rest or moving with a constant velocity  (OR: a frame of reference in which Newton’s law of inertia is valid, that is, a frame in which an object with no unbalanced forces will remain at rest or move at a constant velocity)


223.        *Special Theory of Relativity – Consists of two postulates:

            1) The laws of physics are the same in all inertial reference frames.

            2)  The speed of light in a vacuum is the same for all observers.

224.        *Simultaneity – Two events occurring at different points in space and which are simultaneous for one observer cannot be simultaneous for another observer in a different frame of reference.

225.        Light Clock – a beam of light reflected between two parallel mirrors used to measure time

226.        *Proper Time Interval – the time between events as measured in a frame where the events take place at the same point in space (NOTE: This is the shortest possible time that any observer could correctly record for the event and is usually the time measured in the moving frame of reference.)

227.        Time Dilation – an effect of relativity in which moving clocks run slow

228.        Lorentz Factor (γ) – a relativistic factor that varies from approximately 1 at low velocities to approaching infinity near the speed of light

229.        *Proper Length – the length of an object recorded in a frame of reference where the object is at rest.  (NOTE:  This is the greatest possible length that could be recorded for an object.)

230.        Length Contraction – an effect of relativity in which the separation between two points  in space contracts if there is relative motion in that direction

231.        Twin Paradox – different observers’ measurements of the time taken for a journey at speeds close to the speed of light will not be the same  (NOTE: Since one of the twins has to accelerate in the spaceship, this is no longer a symmetrical situation for the twins.  The space journeying twin records a shorter time measurement (“ages less.”))

232.        Hafele-Keating Experiment – a 1971 test of the predictions of time dilation in which atomic clocks were put in aircraft and flown, east and west, around the world and then compared with clocks that remained fixed in the same location on Earth (NOTE: The clock flying eastward, being the fastest relative to the surface of the Earth, recorded the smallest elapsed time.) (NOTE: The experiment also had to take into account the effects of general relativity since the clocks were at different heights in a gravitational field.)

233.        *Rest Mass – the mass of an object as measured in a frame of reference where the object is at rest (NOTE: Rest mass is an invariant quantity.)

234.        Muon Decay Experiment – an experiment comparing the number of muons in cosmic rays that reach the Earth’s surface without decaying as compared to the number predicted to hit the surface calculated without using relativity theory (NOTE: The results of this experiment give evidence to support the special theory of relativity)

235.        Michelson-Morley Experiment – an experiment comparing the speed of light measured in two perpendicular directions using interference patterns– originally meant to measure the speed of the Earth through the ether – did not produce any observable difference in the speeds – implies that the ether does not exist and that the result is consistent with the constancy of the speed of light – gives experimental support for one of the postulates of special relativity

236.        Pion Decay Experiment – an experiment involving the decay of a fast-moving pion into two gamma ray photons – indicates that the speed of light in a vacuum is independent of its source

237.        General Theory of Relativity – a more general theory of relativity that takes into account accelerating (non-inertial) reference frames (and the effects of gravity)

238.        *Gravitational Mass – the property of an object that determines how much gravitational force it feels when near another object (NOTE: Different gravitational masses have different gravitational forces acting between them.)

239.        *Inertial Mass – the property of an object that determines how much it accelerates when a given force is applied to it (OR: the ratio of resultant force to acceleration of an object) (NOTE: Different inertial masses have different acceleration s when a force acts on them.)

240.        *Principle of Equivalence – a postulate that states there is no difference between an accelerating frame of reference and a gravitational field

241.        Einstein’s Closed Elevator “Thought Experiment” – an object dropped inside a closed elevator will accelerate toward the floor – could be explained in one of two ways: either the elevator is far from any planet but accelerating upward  or the elevator is at rest on the surface of planet

242.        Spacetime – four dimensional coordinates used to describe any event (three spatial dimensions and time) (NOTE: Moving objects follow the shortest path between two points in spacetime.) (NOTE: Gravitational attraction can be explained by the warping of spacetime.)

243.        Black Holes – a region of spacetime with extreme curvature due to the presence of a mass

244.        Center of a Black Hole (singularity) – the single point to which all mass would collapse

245.        Surface of a Black Hole (event horizon) – where the escape speed is equal to c and within this surface, mass has “disappeared” from the universe

246.        *Schwarzschild Radius (RS) – a particular distance from the center of black hole where the escape velocity is equal to the speed of light

247.        Gravitational Red Shift – a prediction of the general theory relativity in which clocks slow down in a gravitational field (that is, clocks on the ground floor of a building will run slowly as compared with clocks on the top floor)

248.        Eddington Eclipse Measurements – Arthur Eddington’s 1919 measurements during the eclipse of the Sun of the apparent change in position of a star – experimental support for the bending of light by a massive object which is a prediction of general relativity

249.        Pound-Rebka Experiment – measurements in 1960 of the decrease in frequency of a photon as it climbs in a gravitational field – experimental evidence to support gravitational red-shift which is a prediction of general relativity

250.        Atomic Clock Frequency Shift Experiment – experiment comparing two identical atomic clocks, one on the ground and one sent to a high altitude in a rocket – higher altitude clock runs faster - experimental evidence to support gravitational red-shift which is a prediction of general relativity

251.        Shapiro Time Delay Experiments – experiment in which the time taken for a radar pulse to travel to a nearby planet and return is measured – the gravitational field of the Sun affects the time taken – measurements confirm the predictions made by general relativity as to the amount of effect on time – experimental evidence to support gravitational red-shift which is a prediction of general relativity

Wrapping up this guide, it's clear that the definitions and explanations laid out are your arsenal for conquering the IB Physics HL syllabus. As you gear up for Paper 2 and the much-anticipated 2024 exams, remember, mastery of these concepts is your first leap towards academic greatness.

Eager to elevate your preparation and edge closer to that elusive 7? Consider joining review sessions with Rajat Sir. His insights and innovative approach can demystify even the densest physics phenomena, making them as palatable as your favorite meme.

Rajat Sir likes to sprinkle humor into the mix, saying, "Physics isn't just about knowing what makes the apple fall; it's about questioning why the apple doesn't stay up for a change! 🍏✨ Stay curious, embrace the quirks, and let's make learning an adventure. After all, in the world of physics, even gravity is a down-to-earth concept!"

Embrace this mix of wisdom and wit as you journey through IB Physics HL. With the right mindset, dedication, and a dash of humor, acing your exam is not just a possibility but a promise. Let's laugh, learn, and leap towards success together.

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