March 19, 2023
Conservation of energy: |
Energy cannot be created or destroyed |
Dissipated energy / dissipation of energy: |
The energy that is not usefully transferred and stored in less useful ways |
Efficiency: |
Useful energy transferred by a device ÷ total energy supplied to the device |
Elastic potential energy |
Energy stored in an elastic object as a result of it being deformed. For example, a stretched spring |
Hooke’s Law: |
The extension of a spring is directly proportional to the force applied, as long as its limit of proportionality is not exceeded |
Input energy |
Energy supplied to a device |
Power |
The energy transformed or transferred per second. The unit of power is the watt (W) |
Spring constant |
Force per unit extension of a spring |
Useful energy |
Energy transferred to where it is wanted in the way that is wanted |
Wasted energy |
Energy that is not usefully transferred |
Work |
The energy transferred by a force. Work done (joules, J) = force (newtons, N) x distance moved in the direction of the force (metres, m) |
Black body radiation |
The radiation emitted by a perfect black body (a body that absorbs all the radiation that hits it) |
Infrared radiation |
Electromagnetic waves between visible light and microwaves in the electromagnetic spectrum |
Specific heat capacity: |
Energy needed to raise the temperature of 1 kg of a substance by 1 °C |
Thermal conductivity: |
Property of a material that determines the energy transfer through it by conduction |
Biofuel |
Any fuel taken from living or recently living materials, such as animal waste |
Carbon-neutral: |
A biofuel from a living organism that takes in as much carbon dioxide from the atmosphere as is released when the fuel is burned |
Geothermal energy: |
Energy released by radioactive substances deep within the Earth. |
National grid |
The network of cables and transformers used to transfer electricity from power stations to consumers (i.e., homes, shops, offices, factories etc.) |
Nuclear fuel |
Substance used in nuclear reactors that releases energy due to nuclear fission |
Nucleus |
Tiny positively charged object composed of protons and neutrons at the centre of every atom |
Reactor core |
The thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor |
Renewable energy: |
Energy from natural sources that is always being replenished so it never runs out |
Diode |
A non-ohmic conductor that has a much higher resistance in one direction (its reverse direction) than in the other direction (its forward direction) |
Electric field |
A charged object (X) creates an electric field around itself, which causes a non-contact force on any other charged object in the field |
Electrons |
Tiny negatively charged particles that move around the nucleus of an atom |
Ion |
A charged atom or molecule |
LDR |
A resistor whose resistance depends on the intensity of the light incident on it |
light-emitting diode (LED) |
a diode that emits light when it conducts |
line of force in an electric field |
line along which a free positive charge moves long in an electric field |
neutrons |
uncharged particles of the same mass as protons. The nucleus of an atom consists of protons and neutrons |
Ohm’s law |
the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor |
parallel |
components connected in a circuit so that the potential difference is the same across each one |
potential difference |
a measure of the work done, or energy transferred to the lamp by each coulomb of charge that passes through it. The unit of potential difference is the volt (V) |
protons |
positively charged particles with an equal and opposite charge to that of an electron |
resistance |
resistance (in ohms, Ω) = potential difference (in volts, V) ÷ current (in amperes, A) |
series |
components connected in a circuit in such a way that the same current passes through them |
static electricity |
electric charge stored on insulated objects |
thermistor |
a resistor whose resistance depends on the temperature of the thermistor |
alternating current (a.c.) |
electric current in a circuit that repeatedly reverses its direction |
direct current (d.c.) |
electric current in a circuit that is in one direction only |
earth wire |
the wire in a mains cable used to connect the metal case of an appliance to earth |
fuse |
a fuse contains a thin wire that melts and cuts the current off if too much current passes through it |
live wire |
the mains wire that has a voltage that alternates in voltage (between +325 V and -325 V in Europe) |
neutral wire |
the wire of a mains circuit that is earthed at the local substation so its potential is close to zero |
oscilloscope |
a device used to display the shape of an electrical wave |
plugs |
a plug has an insulates case and is used to connect the cable from an appliance to a socket |
step-down transformers |
electrical device used to step-down the size of an alternating potential difference |
step-up transformers |
electrical device used to step-up the size of an alternating potential difference |
three-pin plug |
a three-pin plug has a live pin, a neutral pin and an earth pin |
boiling point |
temperature at which a pure substance boils or condenses |
Boyle’s Law |
for a fixed mass of gas at constant temperature, its pressure multiplied by its volume is constant |
density |
mass per unit volume of a substance |
freezing point |
the temperature at which a pure substance freezes |
internal energy |
the energy of the particles of a substance due to their individual motion and positions |
latent heat |
the energy transferred to or from a substance when it changes its state |
melting point |
temperature at which a pure substance melts or freezes (solidifies) |
physical change |
a change in which no new substances are produced |
pressure |
force per unit cross-sectional area for a force acting on a surface at right angles to the surface. The unit of pressure is the pascal (Pa) or newton per square metre (N/m2) |
specific latent heat of fusion Lf |
energy needed to melt 1 kg of a substance with no change of temperature |
specific latent heat of vaporisation Lv |
energy needed to boil away 1 kg of a substance with no change of temperature |
boiling point |
temperature at which a pure substance boils or condenses |
Boyle’s Law |
for a fixed mass of gas at constant temperature, its pressure multiplied by its volume is constant |
density |
mass per unit volume of a substance |
freezing point |
the temperature at which a pure substance freezes |
internal energy |
the energy of the particles of a substance due to their individual motion and positions |
latent heat |
the energy transferred to or from a substance when it changes its state |
melting point |
temperature at which a pure substance melts or freezes (solidifies) |
physical change |
a change in which no new substances are produced |
pressure |
force per unit cross-sectional area for a force acting on a surface at right angles to the surface. The unit of pressure is the pascal (Pa) or newton per square metre (N/m2) |
specific latent heat of fusion Lf |
energy needed to melt 1 kg of a substance with no change of temperature |
specific latent heat of vaporisation Lv |
energy needed to boil away 1 kg of a substance with no change of temperature |
activity |
the number of unstable atoms that decay per second in a radioactive source |
alpha radiation (α) |
alpha particles, each composed of two protons and two neutrons, emitted by unstable nuclei |
atomic number |
the number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number |
beta radiation (β) |
beta particles that are high energy electrons created in, and emitted from, unstable nuclei |
chain reaction |
reactions in which one reaction causes further reactions, which in turn cause further reactions, etc. |
count rate |
the number of counts per second detected by a Geiger counter |
gamma radiation (γ) |
electromagnetic radiation emitted from unstable nuclei in radioactive substances |
half-life |
average time taken for the number of nuclei of the isotope (or mass of the isotope) in a sample to halve |
ionisation irradiated |
any process in which atoms become charged an object that has been exposed to ionising radiation |
isotopes |
atoms with the same number of protons and different numbers of neutrons |
mass number |
the number of proton and neutrons in a nucleus |
moderator |
substance in a nuclear reactor that slows down fission neutrons |
nuclear fission |
the process in which certain nuclei (uranium-235 and plutonium-239) split into two fragments, releasing energy and two or three neutrons as a result |
nuclear fission reactor |
reactors that release energy steadily due to the fission of a suitable isotope, such as uranium-235 |
nuclear fusion |
the process where small nuclei are forced together to fuse and form a larger nucleus |
radioactive contamination |
the unwanted presence of materials containing radioactive atoms on other materials |
reactor core |
the thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor |
displacement |
distance in a given direction |
driving force |
force of a vehicle that makes it move (sometimes referred to as motive force) |
effort |
the force applied to a device used to raise a weight or move an object |
force multiplier |
a lever used so that a weight or force can be moved by a smaller force |
forces |
a force (in newtons, N) can change the motion of an object |
free-body force diagram |
a diagram that shows the forces acting on an object without any other objects or forces shown |
friction |
the force opposing the relative motion of two solid surfaces in contact |
load |
the weight of an object raised by a device used to lift the object, or the force applied by a device when it is used to shift an object |
magnitude |
the size or amount of a physical quantity |
moment |
the turning effect of a force defined by the equation: moment of a force (in newton metres, Nm) = force (in newtons, N) x perpendicular distance from the pivot to the line of action of the force (in metres, m) |
Newton’s first law of motion |
if the resultant force on an object is zero, the object stays at rest if it is stationary, or it keeps moving with the same speed in the same direction |
Newton’s third law of motion |
when two objects interact with each other, they exert equal and opposite forces on each other |
parallelogram of forces |
a geometrical method used to find the resultant of two forces that do not act along the same line |
principle of moments |
for an object in equilibrium, the sum of all the clockwise moments about any point = the sum of all the anti-clockwise moments about that point |
resultant force |
a single force that has the same effect as all the forces acting on the object
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scalar |
a physical quantity, such as mass or energy, that has magnitude only (unlike a vector which has magnitude and direction) |
vector |
a vector is a physical quantity, such as displacement or velocity, that has a magnitude and a direction (unlike a scalar which has magnitude only) |
acceleration |
change of velocity per second (in metres per second per second, m/s2) |
deceleration |
change of velocity per second when an object slows down |
displacement |
distance in a given direction |
gradient (of a straight line graph) |
change of the quantity plotted on the y-axis divided by the change of the quantity plotted on the x-axis |
tangent |
a straight line drawn to touch a point on a curve so it has the same gradient as the curve at that point |
velocity |
speed in a given direction (in metres/second, m/s) |
braking distance |
the distance travelled by a vehicle during the time it takes for its brakes to act |
conservation of momentum |
in a closed system, the total momentum before an event is equal to the total momentum after the event. Momentum is conserved in any collision or explosion, provided no external forces act on the objects that collide or explode |
directly proportional |
a graph will show this if the line of best fit is a straight line through the origin |
elastic |
a material is elastic if it is able to regain its shape after it has been squashed or stretched |
extension |
the increase in length of a spring (or a strip of material) from its original length |
gravitational field strength, g |
the force of gravity on an object of mass 1 kg (in newtons per kilogram, N/kg). It is also the acceleration of free fall |
inertia |
the tendency of an object to stay at rest or to continue in uniform motion |
limit of proportionality |
the limit for Hooke’s law applied to the extension of a stretched spring |
mass |
the quantity of matter in an object – a measure of the difficulty of changing the motion of an object (in kilograms, kg) |
momentum |
this equals mass (in kg) x velocity (in m/s) |
Newton’s second law of motion |
the acceleration of an object is proportional to the resultant force on the object, and inversely proportional to the mass of the object |
stopping distance |
the distance travelled by the vehicle in the time it takes for the driver to think and brake |
terminal velocity |
the velocity reached by an object when the drag force on it is equal and opposite to the force making it move |
thinking distance |
the distance travelled by the vehicle in the time it takes the driver to react |
weight |
the force of gravity on an object (in newtons, N) |
upthrust |
the upward force that acts on a body partly or completely submerged in a fluid |
amplitude |
the height of a wave crest or trough of a transverse wave from the rest position. For oscillating motion, the amplitude is the maximum distance moved by an oscillating object from its equilibrium position |
compression |
squeezing together |
echo |
reflection of sound that can be heard |
electromagnetic waves |
electric and magnetic disturbances that transfer energy from one place to another |
frequency |
the number of wave crests passing a fixed point every second |
longitudinal waves |
waves in which the vibrations are parallel to the direction of energy transfer |
mechanical wave |
vibration that travels through a substance |
oscillate |
move to and fro about a certain position along a line |
primary seismic wave (P-wave) |
longitudinal waves that push or pull on the material that they move through as they travel through the Earth |
rarefaction |
stretched apart |
reflection |
the change of direction of a light ray or wave at a boundary when the ray or wave stays in the incident medium |
refraction |
the change of direction of a light ray when it passes across a boundary between two transparent substances (including air) |
secondary seismic wave (S-wave) |
transverse waves that shake the Earth side to side as they pass through |
seismic waves |
sound wave at frequency greater than 20 000 Hz (the upper frequency limit of the human ear) |
speed |
the speed of an object (metres per second) = distance moved by the object (metres) ÷ time taken to move the distance travelled (seconds) |
transmission/transmitted |
a wave passing through a substance |
transverse wave |
a wave where the vibration is perpendicular to the direction of energy transfer |
ultrasound wave |
sound wave at frequency greater than 20 000 Hz (the upper frequency limit of the human ear) |
vibrate |
oscillate (move to and fro) rapidly about a certain position |
wavelength |
the distance from one wave crest to the next |
carrier waves |
waves used to carry any type of signal |
charge-coupled device (CCD) |
an electronic device that creates an electronic signal from an optical image formed on the CCD’s array of pixels |
contrast medium |
an X-ray absorbing substance used to fill a body organ so the organ can be seen on a radiograph |
electromagnetic spectrum |
the continuous spectrum of electromagnetic waves |
ionisation |
any process in which atoms become charged |
microwaves |
electromagnetic waves between infrared radiation and radio waves in the electromagnetic spectrum |
optical fibre |
thin glass fibre used to transmit light signals |
radiation dose |
amount of ionising radiation a person receives |
radio waves |
electromagnetic waves of wavelengths greater than 0.10m |
ultraviolet radiation (UV) |
electromagnetic waves between visible light and X-rays in the electromagnetic spectrum |
wave speed |
the distance travelled per second by a wave crest or trough |
white light |
light that includes all the colours of the spectrum |
angle of incidence |
angle between the incident ray and the normal |
angle of reflection |
angle between the reflected ray and the normal |
concave (diverging) lens |
a lens that makes parallel rays diverge (spread out) |
convex (converging) lens |
a lens that makes light rays parallel to the principal axis converge (meet) at a point |
diffuse reflection |
reflection from a rough surface - the light rays are scattered in different directions |
focal length |
the distance from the centre of a lens to the point where light rays parallel to the principal axis are focused (or, in the case of a diverging lens, appear to diverge from) |
magnification |
the image height ÷ the object height |
magnifying glass |
a converging lens used to magnify a small object which must be placed between the lens and its focal point |
normal |
straight line through a surface or boundary perpendicular to the surface or boundary |
opaque object |
an object that light cannot pass through |
principal focus |
the point where light rays parallel to the principal axis of a lens are focused (or, in the case of a diverging lens, appear to diverge from) |
real image |
an image formed by a lens that can be projected on a screen |
refraction |
the change of direction of a light ray when it passes across a boundary between two transparent substances (including air) |
specular reflection |
reflection from a smooth surface. Each light ray is reflected in a single direction |
translucent object |
an object that allows light to pass through, but the light is scattered or refracted |
transparent object |
an object that transmits all the incident light that enters the object |
virtual image |
an image, seen in a lens or a mirror, from which light rays appear to come after being refracted by a lens or reflected by a mirror |
alternator |
an alternating current generator |
dynamo |
a direct-current generator |
electromagnet |
an insulated wire wrapped round an iron bar that becomes magnetic when there is a current in the wire |
electromagnetic induction |
the process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of force of a magnetic field |
Fleming’s left-hand rule |
a rule that gives the direction of the force on a current-carrying wire in a magnetic field according to the directions of the current and the field |
generator effect |
the production of a potential difference using a magnetic field |
induced magnetism |
magnetism of an unmagnetised magnetic material by placing it in a magnetic field |
magnetic field |
the space around a magnet or a current-carrying wire |
magnetic field line |
line in a magnetic field along which a magnetic compass points – also called a line of force |
magnetic flux density |
a measure of the strength of the magnetic field defined in terms of the force on a current-carrying conductor at right angles to the field lines |
motor effect |
when a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field |
solenoid |
a long coil of wire that produces a magnetic field in and around the coil when there is a current in the coil |
split-ring commutator |
metal contacts on the coil of a direct current motor that connects the rotating coil continuously to its electric power supply |
step-down transformer |
electrical device that is used to step-down the size of an alternating potential difference |
step-up transformer |
electrical device that is used to step-up the size of an alternating potential difference |
transformer |
electrical device used to change an (alternating) voltage. See also step-up transformer and step-down transformer |
Big Bang theory |
the theory that the universe was created in a massive explosion (the Big Bang), and that the universe has been expanding ever since |
black dwarf |
a star that has faded out and gone cold |
black hole |
an object in space that has so much mass that nothing, not even light, can escape from its gravitational field |
centripetal force |
the resultant force towards the centre of a circle acting on an object moving in a circular path |
cosmic microwave background radiation (CMBR) |
electromagnetic radiation that has been travelling through space ever since it was created shortly after the Big Bang |
dark matter |
matter in a galaxy that cannot be seen. Its presence is deduced because galaxies would spin much faster if their stars were their only matter |
main sequence |
the main sequence is the life stage of a star during which it radiates energy because of fusion of hydrogen nuclei in its core |
neutron star |
the highly compressed core of a massive star that remains after a supernova explosion |
protostar |
the concentration of dust clouds and gas in space that forms a star |
red giant |
a star that has expanded and cooled, resulting in it becoming red and much larger and cooler than it was before it expanded |
red supergiant |
a star much more massive than the Sun will swell out after the main sequence stage to become a red supergiant before it collapses |
red-shift |
increase in the wavelength of electromagnetic waves emitted by a star or galaxy due to its motion away from us. The faster the speed of the star or galaxy, the greater the red-shift is |
supernova |
the explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses on to the core and rebounds |
white dwarf |
a star that has collapsed from the red giant stage to become much hotter and denser |