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Physics Definitions
G481 Mechanics
Scalar quantity
Vector quantity
Displacement
Instantaneous speed
Average speed
Velocity
Acceleration
The Newton
Terminal Velocity
Centre of gravity
Torque of a couple
Couple
Moment of a force
Principle of moments
Conditions necessary for an
object to be in equilibrium
Thinking Distance
Braking distance
Stopping distance
Work done
The Joule
principle of conservation of
energy
Power
The Watt
Stress
Strain
Young’s modulus
Ultimate tensile strength
Hooke’s law
Elastic deformation
Plastic deformation
Elastic Limit
A quantity that has magnitude / size only
A quantity that has (both) magnitude / size and direction
Distance moved in a certain direction
Speed at a particular time. This may be distance ÷ time or the gradient of
a tangent on a speed – time graph.
Rate of change of distance OR distance travelled ÷ time taken
Rate of change of displacement OR change in displacement ÷ time
Rate of change of velocity OR change in velocity ÷ time
(Force is 1 N ) when a 1 kg mass has an acceleration of 1 ms-2
This occurs when the weight of a body = the drag /air resistance forces on
the body.
Point on a body where the entire weight appears to act
one of the forces × perpendicular distance (between forces)
A pair of equal and opposite forces (with their lines of action separated by
a distance)
moment = force x perpendicular distance from pivot / axis / point
For equilibrium of an object the sum of clockwise moments about a point
= sum of anticlockwise moments about the same point
Net / total / resultant force = 0
Net / total torque / moment = 0
The distance travelled (by the car) from when the driver sees a problem
and the brakes are applied.
The distance travelled (by the car) whilst the brakes are applied and the
car stops.
thinking distance + braking distance
force x distance moved in the direction of the force
The energy needed to move an object one metre with a force of 1N (1Nm).
Energy cannot be created or destroyed; it can only be
transferred/transformed into other forms or The (total) energy of a
system remains constant or (total) initial energy = (total) final energy
Work (done)/time or energy/time or rate of work done
One Joule per second.
Force per unit area
Extension per unit length
Stress / strain
Maximum stress material can withstand (before fracture)
extension (or compression) α force as long as elastic limit is not exceeded
Material returns to its original length / shape/ size when the force /
stress is removed
Material does not return to its original length / shape/ size when the
force / stress is removed
Point beyond which an object will not return to its original
length/shape/size when the load is removed.
G482 Electrons Photons and Waves
Conventional current
Current moves from + to – (of battery in circuit)
Electron flow in a circuit
Electrons move from – to + (terminals of a battery in a circuit)
The Coulomb
The ampere second (As)
Mean drift velocity
The average displacement/distance traveled of the electrons along the
wire per second.
Kirchoff’s 1st law
(sum of/total) current into a junction equals the (sum of/total) current
out. This is an example of conservation of charge.
Potential difference
The electrical energy converted to other forms per coulomb of charge
flowing between two points in a circuit.
Electromotive force
The electrical energy given to each coulomb of charge in the battery
/power supply.
Resistance
p.d./current
The Ohm
The volt per ampere (VA-1)
Resistivity
ρ = RA/l with terms defined
Kilowatt hour
(a unit of) energy equal to 3.6 MJ or 1 kW used for 1 h
Kirchoff’s 2nd Law
(sum of) e.m.f.s = sum /total of p.d.s/sum of voltages (in a loop). This
is an example of conservation of energy.
Terminal p.d.
Potential difference between the terminals of a power supply
Amplitude
Maximum displacement from the rest position.
Wavelength
Distance between (neighbouring) identical points/points with same
phase (on the wave) i.e. crest – crest.
Period
The time taken for one complete oscillation.
Frequency
number of oscillations (at a point) per unit time/second.
Intensity
rate of transfer of energy per unit area at right angles to the wave
velocity i.e. power ÷ cross-sectional area
Phase difference
The amount by which one wave leads or lags behind another wave.
Speed of a wave
distance traveled by the wave (energy) per unit time/second
Reflection
Change in direction of a wave when it meets an impenetrable barrier
(bounces off)
Refraction
The sudden change in direction of a wave as it crosses the boundary
from one material to another. It is caused by a sudden change in
speed. NB wavelength changes but frequency does not.
Diffraction
The spreading out of a wave after passing through a gap or around an
edge
Interference
when (two) waves meet/combine/interact/superpose, etc. (at a point)
there is a change in overall intensity/displacement
Plane polarised waves
(transverse) waves with oscillations in one plane only.
Malus law
Intensity of polarized light transmitted I = I0 cos2 θ
Principle of superposition When two waves pass through the same space at the same time the
of waves
resultant displacement is the algebraic sum of the displacements
produced by each wave.
Coherence
Path difference
Constructive interference
Destructive interference
Progressive wave
Stationary wave
constant phase difference/relationship (between the waves)
The extra distance travelled by one wave compared to the other.
Two waves arrive at a point in phase so their displacements add up.
Two waves arrive at a point out of phase so their displacements cancel.
Waves which always travel away from their source.
A wave produced from the interference of a progressive wave and its
reflection. A wave with zero speed of travel, because it is fixed
between two points.
Node
node occurs where the amplitude/displacement is (always) zero
Antinode
antinode occurs where the amplitude (of the standing wave) takes the
maximum (possible) value
Fundamental mode of
The lowest frequency standing wave that can be produced (on a string
vibration
or in a pipe).
Harmonics
Odd or even integer multiples of the fundamental frequency that
produce a stationary wave.
Photon
a quantum/packet/particle of energy of electromagnetic radiation.
The electron volt (eV)
an eV is the energy acquired by an electron accelerated/moves
through a p.d. of 1 V. 1 eV = 1.6 x 10-19 J
Work function
The minimum energy (of a photon) that will produce a photoelectron.
Threshold frequency
The minimum frequency (of light) needed to produce photoelectrons.
Intensity
intensity is the (incident) energy per unit area per second or power per
unit area or power per m2
Emission line spectrum
The light emitted from (excited isolated) atoms producing a series of
(sharp/bright/coloured) lines against a dark background
absorption spectrum
a series of dark lines (appears against a bright background /within a
continuous spectrum).
Continuous spectrum
A spectrum where all wavelengths/frequencies/colours are present (in
the radiation).
The de Broglie
Electrons are observed to behave as waves/show wavelike properties
wavelength of an electron after passing through a gap. The electron wavelength depends on its
speed/momentum.
G484 Newtonian World
Newton’s 1st Law
Newton’s 2nd Law
Newton’s 3rd Law
Impulse
S.H.M.
Conservation of linear momentum
Inelastic collision
Conditions necessary for circular
motion
In SHM what is the difference
between displacement and
amplitude.
In SHM what is the difference
between frequency and angular
frequency.
Boyle’s law
Assumptions of the kinetic model
of ideal gases
How a gas exerts a pressure
Conclusions about air molecule
motion from Brownian Motion
observations of smoke particles.
Thermal equilibrium
An object will remain at rest or travel at constant velocity
unless acted on by a (an external unbalanced) force.
Force is proportional to the rate of change of momentum
When one body exerts a force on another the other body
exerts an equal (in magnitude) and opposite (in direction)
force on the first body.
Change in momentum or product of force and time
acceleration is (directly) proportional to displacement and is
directed in the opposite direction to the displacement /
towards the equilibrium position.
Total momentum is constant or total momentum before =
total momentum after a collision.
One in which there is some loss of kinetic energy or KE
before is not equal to the KE after the collision.
The resultant or net or overall force acts (on object)
perpendicular to the velocity or towards the centre of the
circle
Displacement is the distance (of the body) from an
equilibrium position.
Amplitude is the maximum displacement
Frequency is the number of oscillations/cycles per unit
time/second
Angular frequency is product of 2π x frequency or
2πperiod.
Pressure is inversely proportional to volume for a fixed
mass of gas at constant temperature
1. particles move with rapid, random motion (WTTE)
2. elastic collisions.
3. negligible (or zero) volume of atoms (compared with
volume of container).
4. no intermolecular forces (except during collisions)/all
internal energy is KE.
5. collision time negligible (compared to time between
collision).
1. molecules make collisions with walls/surface
2. (hence) exerts a force on the wall (or each collision has a
change of momentum)
3. Pressure = force/area
1. air molecules are moving in different
directions/randomly with different speeds.
2. mass/size of air molecules is smaller than smoke particles
No net heat flow between objects or objects are at the same
temperature.
G485 Fields, Particles and Frontiers of Physics
Capacitance
charge per (unit) potential difference allow charge / potential
difference, charge/pd, charge/voltage but not charge / volt,
coulomb /pd (a mixture of quantities and units).
Assumptions of Olbers Paradox
Universe is; static / homogeneous
Universe is: infinite / infinite number of stars
magnetic flux
magnetic flux density x area (perpendicular to field direction)
Allow equation (Φ = BA) with the symbols identified correctly
Faraday’s law
Induced e.m.f is proportional to the rate of change of (magnetic)
flux
The Farad
coulomb per volt Allow: 1 F = 1 CV-1
Hubble’s Law
the process of nuclear fusion in
the core of the Sun
The speed of recession of a galaxy is proportional to its distance
(from Earth / observer)
1.Protons / hydrogen nuclei to produce He nuclei (positrons and
neutrinos)
2. There is electrostatic repulsion (between the protons) / The
protons repel (each other because of their positive charge)
7
the formation of a star such as
our Sun
evolution of a star that is much
more massive than our Sun
Observations supporting the
idea of the big bang
3. High temperatures / 10 K needed (for fusion)
4. (At high temperatures some of the fast moving) protons come
close enough to each other for the strong (nuclear) force (to
overcome the electrostatic repulsion)
5. High density / pressure (in the core of the Sun)
6. There is a decrease in mass, hence energy is released /
products have greater binding energy
1. Gas / dust (cloud) drawn together by gravitational forces
2. Loss in (gravitational) PE / KE increases / PE changes KE /
temperature increase
3. Fusion of protons / hydrogen nuclei (produces helium nuclei
and energy)
4. A stable star is formed when radiation pressure is equal to
gravitational pressure
5. When hydrogen runs out the outer layers of the star expands /
core shrinks
6. Red giant formed / eventually (the core becomes) a white
dwarf
As above plus
Supernova followed by
Neutron star or Black hole
1. Spectra from galaxies show shift to longer wavelengths
(suggests galaxies are moving away from the Earth)
2. The more distant galaxies are moving faster (than the ones
The Parsec
closer to our galaxy).
3. Existence of microwave background radiation (which is the
same in all directions) / The temperature of universe is 3K (after
cooling due to expansion) / gamma (radiation) became
microwaves (as the universe expanded).
4. Existence of primordial helium (produced in the early stages of
the universe).
5. Temperature fluctuations (predicted and observed)
Parsec is a distance that gives a (stellar) parallax of 1 second (of
o
Piezoelectric effect
Acoustic impedance matching
Spontaneous and random nature
of radioactive decay of unstable
nuclei
The decay constant
The technique of radioactive
carbon-dating
The use of image intensifiers and
contrast media when X-rays are
used to produce images of
internal body structures
Difference between a CAT scan
and an X-ray
How ultrasound scanning is
used to obtain diagnostic
information about internal
structures of a body.
arc) / 1/3600
The application of a p.d. across a material / crystal causes an
expansion / contraction / vibration
(Acoustic) impedances of media are similar / identical
Spontaneous: the decay cannot be induced / occurs without
external influence.
Random: cannot predict when / which (nucleus) will decay next
The probability of decay of a nucleus per unit time
Allow = A/N with symbols defined.
1. Living plants / animals absorb carbon(-14)
2. Once dead, the plant does not take in any more carbon(-14)
3. The fraction of C-14 to C-12 (nuclei) or number of C-14 (nuclei)
or activity of C-14 (nuclei) is measured in dead and living
samples
4. x =xo e-t used to estimate the age
1. Intensifier used as X-ray would pass through film
2. Intensifier converts X-ray photon to many visible (light)
photons (which are absorbed by film)
3. Lower exposure / fewer X-rays needed
4. Iodine / barium (used as contrast material)
5. High Z number / large attenuation coefficient / large
absorption coefficient (used to improve image contrast)
6. Contrast media are ingested / injected into the body
7. Scan shows outline / shape of soft tissue
Simple X-ray is one directional / produces single image
CT image(s) taken at different angles / X-ray tube is rotated
Computer processes data / image constructed from many slices
1. Pulses of ultrasound (sent into the body)
2.Wave / ultrasound / pulse / signal is reflected (at boundary of
tissue)
3. Time of delay used to determine depth / thickness
4. The fraction of reflected signal is used to identify the tissue