IB Physics Tutor. Definitions and explanations. How to answer correctly and precisely.
All definitions are taken from IB Past Papers (neither books nor just from google) hence are correct, precise and acceptable from IB point of view.
error that is identical for each reading / error caused by zero error in instrument.
average speed is the speed over a period of time/distance; instantaneous speed is the speed at a particular instant in time/point in space.
the resultant force acting on the object must be zero.
mass×velocity; (allow mv with symbols defined).
the rate of change of momentum of a body is equal to/directly proportional to the force acting on the body.
total momentum does not change/is constant; (do not allow “momentum is conserved”)
provided external force is zero / no external forces / isolated system.
) if object A exerts a force on object B, then object B (simultaneously) exerts an equal and opposite force on object A / every action has an equal and opposite reaction.
change in momentum of the body.
momentum and kinetic energy are both conserved.
The temperature of the objects only.
the energy required to change the temperature (of a substance) by 1K/°C/unit degree;
of mass 1 kg / per unit mass.
(note: thermal capacity is energy required to raise the temperature of a whole object not 1 kg by 1 degree and hence is measured in J/K)
(note: energy density is energy per unit volume and measured in J per meter cubed but specific energy is energy per unit mass and is measured in J/kg)
the energy (absorbed/released) when a unit mass/one kg;
of liquid freezes (to become solid) at constant temperature / of solid melts (to become liquid) at constant temperature.
potential energy changes during changes of state / bonds are weakened/broken during changes of state;
potential energy change is greater for vaporization than fusion / more energy is required to break bonds than to
SLH vaporization is greater than SLH fusion.
temperature is a measure of the (average) kinetic energy of the molecules;
at the boiling point, energy supplied (does not increase the kinetic energy) but (only) increases the potential energy of the molecules/goes into increasing the separation of the molecules/breaking one molecule from another
one kilogram of a substance at constant temperature.
energy supplied/bonds broken/heat absorbed;
increases potential energy;
no change in kinetic energy (so no change in temperature);
The thermal energy required to increase the temperature of unit mass of the body by 1K
The amount of substance that contains as many elementary entities as the number of atoms in 12 g of carbon-12.
the mass of one mole of a substance.
The total potential energy and random kinetic energy.
total energy of component particles;
comprises potential energy + (random) kinetic energy;
measure of average kinetic energy of particles;
indicates direction of (natural) flow of thermal energy;
internal energy measured in J and temperature measured in K/°C.
a gas in which there are no intermolecular forces
OR a gas that obeys the ideal gas law/all gas laws at all pressures, volumes and temperatures
OR molecules have zero PE/only KE
point molecules / negligible volume;
no forces between molecules except during contact; (note: therefore, the intermolecular potential energy of the molecules is zero)
motion/distribution is random;
elastic collisions / no energy lost;
obey Newton’s laws of motion;
collision in zero time;
gravity is ignored;
(note: to remember 2 is enough)
Low density and low pressure
(note: high or moderate temperature if question involves temperature)
defined from the equation of state of an ideal gas PV=nRT;
all symbols (PVnT) correctly identified.
«volume has increased and» average velocity/KE remains unchanged
«so» molecules collide with the walls less frequently/longer time between collisions with the walls
«hence» rate of change of momentum at wall has decreased
«and so pressure has decreased»
Energy is transferred to the molecules by the moving piston.
proportional to T.
thermal energy: (non-mechanical) energy transferred between two objects (at different temperatures);
internal energy: (total) potential energy and (random) kinetic energy of the molecules/particles (of the gas).
(note: for ideal gas potential energy is zero, hence total (internal) energy = total random kinetic energy)
the internal energy of the iron is equal to the total KE plus PE of the molecules; the molecules of an ideal gas have only KE so internal energy is the total KE of the molecules.
net displacement of the medium;
equals the resultant/sum of individual displacements.
(periodic) motion in which acceleration/restoring force is proportional to the displacement from a fixed point;
directed towards the fixed point / in the opposite direction to the displacement.
travelling wave reflects at…
at certain fixed frequencies
incident wave and reflected wave
superpose (or interfere)
to produce a standing wave
(note: these are key phrases which could be used in explanation of formation of standing waves for different situations (problems), but you can add something according to the question, e.g. producing nodes and antinodes, etc.»)
wave travels down string and is reflected;
incident and reflected waves interfere/add/superpose to give a standing wave.
travelling waves move down the tube;
which then interfere with the reflected waves (from the closed end of the tube/surface of the water);
(OR superposition as an alternative to interference).
T: energy (crests/disturbances) moves
S: no propagation
T: all particles oscillate with same amplitude
S: particles oscillate with different amplitudes
T: particles separated by integer number of wavelengths are in phase
S: all particles within two consecutive nodes are in phase
a varying magnetic and electric field at right angles to each other;
vibration of E and B fields at right angles to the direction of propagation of the wave;
same speed in a vacuum.
light in which the electric field vector oscillates on one plane/direction.
waves of different wavelength/frequency;
travel at different velocities;
the index of refraction of the medium depends on the wavelength/frequency.
during simple harmonic motion the charge oscillates/accelerates;
(oscillating/accelerating) charges radiate/produce (varying) electric/magnetic fields / produce electromagnetic waves.
partially plane polarized.
the direction of oscillation of the particles of the medium;
(must be “particles”)
is in the direction of energy propagation;
ray: direction of wave travel / energy propagation;
wavefront: line that joins points with same phase/of same crest/trough;
ray normal/at right angles/perpendicular to wavefront.
mention of perpendicular/right angle/90° angle for transverse and parallel for longitudinal;
clear comparison between direction of energy propagation and direction of vibration/oscillation of particles for both
constant phase difference.
spreading out a wave when it meets an aperture/gap/slit/obstacle.
note: the greater the wavelength is the greater diffraction is. Why do TV’s require high antennas, whereas radio does not? Wavelength for radio waves is much greater, hence radio signals easily bend around buildings.
The insect will not be detected (by sound wave, for example) if the length of the insect is much smaller then the wavelength of sound wave. Also there is a limit to the magnification of a light micriscope. Wavelength of light about micrometer and if length of object is (of order or) less then micrometer there will be very little reflection. Light waves just bend around the object. To see something light must be reflected/
the force between two (point) charges;
is inversely proportional to the square of their separation and (directly) proportional to (the product of) their
The force exerted per unit charge;
on a positive small/test charge.
The rate of flow of electric charge.
the work done per unit charge in moving a quantity of charge completely around a circuit / the power delivered per unit current / work done per unit charge made available by a source;
place voltmeter across battery.
ratio potential difference across the component to current in the component.
The resistance of a conductor is constant provided that the temperature is constant.
OR potential difference across the component is directly proportional to the current in the component providing the temperature/physical conditions are constant.
. force per unit length between parallel current-carrying conductors.
conduction is due to movement of the free electrons (transferring charge around circuit);
tungsten is a good electrical conductor with large numbers of free electrons;
glass is a poor electrical conductor with few/no free electrons.
The Earth and the Sun behave as point masses.
) astronauts and spaceship have the same acceleration;
acceleration is towards (centre of) planet;
so no reaction force between astronauts and spaceship;
astronauts and spaceships are both falling towards the (centre of the) planet;
at the same rate;
so no reaction force between astronauts and spaceship.
Force acting per unit mass on a small mass placed at the point.
velocity changing so accelerating.
the (attractive) force between two (point) masses is directly proportional to the product of the masses; and inversely proportional to the square of the distance (between their centres of mass).
Use of equation is acceptable if all five quantities defined.
atomic spectra have discrete line structures / only discrete frequencies/wavelengths;
photon energy is related to frequency/wavelength;
photons have discrete energies;
photons arise from electron transitions between energy levels;
which must have discrete values of energy.
nuclides/atom/element/nucleus/nuclei that have different nucleon/neutron numbers but same proton number/are same element
one twelfth of the mass of a carbon-12 atom;
Do not allow nucleus!
time for the activity of a sample to halve / time for half the radioactive nuclei to decay.
particle with no internal structure / cannot be broken down further.
a particle that mediates/carries/transmits one of the fundamental forces / a particle that is exchanged between two particles when undergoing one of the fundamental interactions
Electron / neutrino / any lepton / any named exchange particle.
shine white light through;
a tube of the gas;
then observe with spectroscope/grating/prism.
continuous spectrum crossed by dark lines;
dark lines formed by the absorption of photons;
the absorbed photons have specific/discreet wavelengths;
indicating discreet differences in energy;
which can only be explained by existence of energy levels.
(a species of atom that is characterized by) the constitution of its nucleus / the number of protons and neutrons in the nucleus.
. the paths taken by ions in a (Bainbridge) mass spectrometer.
emission of (alpha/beta/gamma) particles/photons/electromagnetic radiation;
nucleus becomes more (energetically) stable;
constant probability of decay (per unit time);
is random process;
activity/number of unstable nuclei in sample reduces by half over constant time intervals/exponentially;
not affected by temperature/environment / is spontaneous process.
a particle with the same mass but opposite quantum numbers/charge.
exchange particles are virtual particles/bosons;
that mediate/carry/transmit the weak/strong/em force between interacting particles.
photon / graviton / Z / Higgs.
the (minimum) energy required to completely separate the nucleons of a nucleus / the energy released when a nucleus is assembled.
The mass of the sample.
power/energy per second emitted proportional to surface area;
and proportional to fourth power of absolute temperature / temperature in K.
(Equation with symbols defined is acceptable.)
effect caused by gas such as H O/NH /CH /CO /greenhouse gas in the atmosphere;
gas absorbs outgoing (long wave) radiation from Earth; (note: due to process called resonance)
gas re-radiates including some of the energy back to Earth.
more greenhouse gases means that there is more absorption of outgoing radiation;
therefore more energy returns to Earth;
leading to a further/greater increase in the temperature of the surface (of Earth).
photovoltaic cells generate emf/electricity;
solar panels generate thermal energy/heat.
. To slow down neutrons.
kinetic energy is removed from the neutrons.
. the Sun’s radiated energy.
kinetic energy of wind transferred to (rotational) kinetic energy of turbine/blades;
kinetic energy changed to electrical energy in generator/dynamo.
Generator/dynamo must be mentioned.
the speed of the air/wind cannot drop to zero;
wind turbulence / frictional losses in turbine/any moving part / resistive heating in wires.
wind is renewable so no resources used up / wind is free / no chemical pollution / no carbon dioxide emission / does
not contribute to greenhouse effect / is “scalable” i.e. many sizes of turbine possible;
expensive initial cost / large land area needed / wind not constant / effect on movement of birds / aesthetically
unpleasant / noise pollution / high maintenance costs / best locations far from population centres / low energy density.
U-238 is much more common than U-235 in ore;
U-235 is more likely to undergo fission / critical amount of U-235 required to ensure fission / OWTTE;
U-238 absorbs neutrons;
U-238 reduces reaction rate in reactor.
Their rate of consumption is much greater than the rate at which they are being produced.
it can no longer be used to do work / not available in useful form.
no radioactive waste;
no radiation risks to users;
lower expense of decommissioning / easier to decommission / easier to install / lower set-up cost;
transportation and storage less hazardous/safer;
cannot be used for military purposes;
fossil fuels can be extracted/found more easily;
no chance of catastrophic accident/meltdown/Chernobyl.
a change in the observed frequency/wavelength of a wave;
when there is relative motion of observer and source.
light reflects from the top surface of the oil and the top surface of the water;
mention of interference/superposition;
path difference exists between both reflected rays;
different wavelengths interfere constructively for different positions/angles (hence colours appear/shift).
the first minimum of one diffraction pattern;
falls on central maximum of other diffraction pattern.
Force acting per unit mass on a small mass placed at the point.
(minimum) speed of object to escape gravitational field of a planet/travel to infinity;
at surface of planet;
without (further) energy input.
electric force per unit charge;
acting on a small/point positive (test) charge.
work done per unit mass;
in bringing (test) mass from infinity to point;
reference to small/point (test) mass.
the work done per unit charge;
when a small/test/point positive charge; (charge sign is essential)
is moved from infinity to the point.
the product of (the magnitude of) the normal component of magnetic field strength;
and area through which it passes/with which it is associated;
φ = BA cos θ ;
all terms defined/shown on a diagram.
. the rate of change of magnetic flux linkage.
charge stored by the device for a potential difference of 1V across the device.
ratio of charge stored to potential difference.
induced emf/induced current acts so as to oppose the change causing it.
Scattering of electrons by a crystal.
ejection of electron from metal surface following absorption of em radiation/photon.
minimum energy/work required to remove an electron (from the surface of the substance).
measure of the probability of finding an electron (at a particular place and time).
the (square of the) amplitude gives the probability of finding the electron at a given point in space.
all particles have an associated wavelength/behave like waves;
lambda=h/p with and symbols defined/described using terms.
the (square of the) amplitude gives the probability of finding the electron at a given point in space.
the probability of decay of a nucleus per unit time.
light consists of discrete packets/quanta/bundles of energy/particle;
each photon has an energy of hf (where h is the Planck constant and f is the frequency of light);
the energy of a (em) wave depends on amplitude (not frequency);
so increasing the intensity should have resulted in electrons being emitted (at any frequency);
the work function is the minimum energy required to eject an electron from a metal surface;
if the photon energy (hf) is less than the work function then no emission will take place;
mention of photons;
of quantized energy / energy is hf;
one to one correspondence with electrons and photons;
(so arrival of light causes emission straightaway);
intensity is a measure of the number of photons not the individual photon energy.
idea that total energy released in the decay is fixed;
beta particle energies are less than this value/continuous;
the neutrino is postulated to account for this “missing” energy.