Physics General Definitions.txt
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Displacement
Position of an object relative to its starting position.

Velocity
Rate of change of displacement.

Speed
Rate of change of distance.

Acceleration
Rate of change of velocity.

Newton's First Law
An object continues in uniform motion in a straight line/ at rest unless a resultant force acts.

Newton's Second Law
The acceleration of an object is proportional to and in the same direction as its resultant force.

Newton's Third Law
When 2 objects react, the exert equal and opposite forces on each other.

Linear Momentum
The product of mass and velocity.

Impulse
Change in momentum.

Law of conservation of momentum
Momentum of object in system stays the same in a closed system.

Work
Force X distance moved in direction of force.

Kinetic Energy
The energy an object has due to it's motion

Change in GPE
The energy an object has due to its position above the Earth.

Elastic Collision
KE is conserved and objects bounce off with the same speed it did before in opposite directions.

Inelastic Collision
Maximum loss of KE, objects stick together & momentum is still conserved.

Explosion
Objects move away from each other, internal energy becomes KE.

Efficiency
Ratio of work out: energy put in.

Mole
Amount of substance that has the same number of molecules as the number of of molecules as the number of atoms in 12g of C12.

Molar Mass
Mass of 1 mole of the substance.

Avogadro's Constant
Number of molecules in 1 mole = 6.022 × 10²³

Specific Heat Capacity
The energy needed to increase the temperature of of 1 kilo of an object by 1K.

Thermal Capacity
The energy needed to increase the temperature of an object by 1K.

Specific Latent Heat
Amount of heat needed to change the state of 1 kilo of a substance WITHOUT a change in temperature.

Pressure
Force per unit area.

Displacement (SHM)
Distance away a particle is from its equilibrium position.

Amplitude (SHM)
Maximum displacement of a particle from its equilibrium position.

Frequency (SHM)
Number of oscillations produced per second.

Period (SHM)
Time taken for a complete oscillation.

Phase Difference (SHM)
The fraction of an oscillation that one wave moves behind another.

Simple Harmonic Motion
Motion where the acceleration of an object is proportional to & in the opposite direction to displacement. a = ω2x

Damping
Process where the energy of an oscillating system decreases with amplitude by a dissipative force acting in the opposite direction.

Natural frequency
The frequency that a system naturally oscillates at.

Forced oscillation
An oscillation that occurs & stays , Where an object is forced to oscillate by an external force.

Resonance
When the frequency of a driving force matches the natural frequency of oscillation.

Transverse wave
Oscillations are at 90° to direction of energy transfer/ wave motion.

Longitudinal wave
Oscillations are parallel to direction of energy transfer/ wave motion.

Crest
Point on a wave with maximum positive displacement.

Trough
Point on a wave with maximum negative displacement.

Compression
Region (on a wave) where particles are closer together than they would be in their equilibrium state.

Rarefaction
Region (on a wave) where particles are further apart than they would be in their equilibrium state.

Wavelength
The shortest distance between 2 points on a wave that are in phase.

Wave speed
The speed at which wave fronts pass a stationary observer.

Intensity
The power per unit area received by an observer from a wave.

Principle of superposition
When 2 or more waves of the same type meet, the total displacement at a point on a wave is the displacements of the individual waves added at that point.

Constructive/destructive interference
Phase difference is 0/ out of phase& path difference is a whole 'n' of wavelength/ a fraction of it.

Electric potential difference
Work done per unit charge in moving a positive charge from one point in the (electric) field to another.

Electronvolt
The amount of energy an electron gains by moving through a potential difference of 1 volt.

Electric current
The rate of flow of electrical charge.

Resistance
The ratio of voltage across the material to the current flowing through it.

Ohm's Law
The current through a wire is proportional to the p.d. across it; as long as the temperature is constant.

Electromotive force (emf)
The power supplied by the supply per unit current.

Internal resistance
Resistance of a source (of power).

Gravitational field strength
The force per unit mass experienced by a small test mass placed in the field.

Newton's universal law of gravitation
Any point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to their separation².

Electric field strength
The force per unit charge experienced by a small test charge placed in the field.

Magnetic field strength
 F=BILsinø
 Direction: 90° to field lines.

Nuclide
An atom with a particular nucleus configuration.

Nucleon
A proton or a neutron.

Isotope
An element with the same number of protons but a different number of neutrons.

Radioactive half life
The time taken for the total number of nuclei (of a radioactive substance) to halve.

Unified atomic mass
The mass of ½ of the nucleus of a C12 isotope.

Mass defect
The difference in mass between a nucleus and its separate nucleons.

Binding energy per nucleon
The total binding energy for the nucleus divided by the total number of nucleons

Binding energy
The energy needed to break up a nucleus into its constituent nucleons.

Degraded energy
Energy transferred to surroundings that can no longer do useful work.

Energy density
The mean energy liberated per kg of a fuel.

Fuel enrichment
A process where you increase percentage of U235 to make fission more likely.

Moderator
Slows down fast neutrons to increase the chance of more reactions. (So they don't pass through the nuclei)

Control rod
This absorbs neutrons to control chain reactions.

Heat exchanger
This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. The thermal energy is transferred to heat water, and the steam that is produced turns the turbines.

Photovoltaic cell
Light hits semiconductors & electrons are released/ moved; creating an electric field.

Solar heating panel
Heat goes through glass pane & is absorbed by black pipes with running water in them.

Albedo
The ratio of reflected: incident radiation.

Stefan Boltzmann law
Total power radiated ∝ T⁴ OR P= σAT⁴.

Emissivity
The ratio of power emitted by a body to the power emitted if it was a black body.

Surface heat capacity
The energy needed to raise the temperature of a unit area of a planet's surface by 1K.

Enhanced greenhouse effect
Rising global temperatures due to greenhouse gases being put into the atmosphere because of human activities

Coefficient of volume expansion
The fractional change in volume per degree change in temperature.

Gravitational potential
Work done per unit mass in bringing a test mass from infinity to that point in the field.

Gravitational potential energy
Work done in moving an object from infinity to that point.

Electric potential
The work done per unit charge in bringing a positive test charge from infinity to that point in the field.

Electric potential energy
The work done moving a charge from infinity to a point in an electric field.

Isochoric
Constant volume: no work is done.

Isobaric
Constant pressure: Work done is area under line.

Isothermal
Constant temperature: Work done= area under curve.

Adiabatic
No heat transfer: compression/ expansion. Work is done on/ by gas

Standing waves
Transfer no energy. They have the same amplitude and are in phase. Happens when a wave & its reflection interfere (or just 2 waves)

One dimensional standing wave
Happens when a wave reflects back from a boundary along the route it came.

Doppler Effect
The change in perceived frequency because the source or observer is moving.

Rayleigh criterion
2 points will be resolvable if the first minimum of the diffraction pattern of one source overlaps the central maximum of the diffraction pattern of the second source.

Polarized light
Light with waves that vibrate in 1 plane.

Brewster's angle
Happens when the transmitted ray is 90° to the reflected ray. The angle gives us the angle of incidence needed for planepolarized light.

Polariser
A device that makes polarized light from an unpolarised beam.

Analyser
A polariser used to detect polarised light.

Optically active substance
A substance that rotates the plane of polarisation of light that goes through it.

Stress analysis
If polarised white light is shone on plastic, you can see the stress points where the coloured lines are.

Magnetic flux
A measure of the strength of a magnetic field over a given area/ number of field lines.

Magnetic flux linkage
The product of the magnetic flux and the number of turns in a given coil.

Faraday's law
The size of an induced emf is proportional to the rate of change of flux linkage.

Lenz's law
The direction of an induced current is such that it'll oppose the change causing it.

de Broglie Hypothesis
All particles have a wave like nature.

Electron in a box model
An electron has possible wavelengths like a standing wave on a string so electrons have discrete energies.

Schrödinger's model
This gives the probability of where the electron could be (probability regions called orbitals).

Heisenberg uncertainty principle
 You can only know 1 from each pair:
 momentum & position
 energy & time

Decay constant
Probability of decay of a nucleus per unit time

Radioactive decay law
The activity of a radioactive sample ∝ Number of radioactive nuclei present.

Capacitance
Charge per unit p.d. that can be stored on a capacitor.

Quantum efficiency
The ratio of the number of photoelectrons emitted: the number of photons incident on the pixel.

Magnification
The ratio of the length of the image on the CCD: the length of the object.

Stellar cluster
A group of stars that are physically near each other in space.

Constellation
A pattern of stars as seen from Earth that aren't physically near each other in space.

Light year
The distance that light travels in 1 year.

Luminosity
The total power emitted by a star.

Apparent brightness
The power received per unit area on Earth by a star.

Cepheid
A slightly unstable star that has a regular variation in brightness and luminosity due to a periodic expansion and contraction in its outer layers.

Red giant
 Red
 Comparatively cool
 Large
 Fuse elements other than Hydrogen

Red Supergiant
 Red
 Large Mass
 Large Surface Area
 Large Luminosity
 Low Surface Temperature

White Dwarfs
 Very Small/ Low Surface Area
 Large Surface Temperature
 White

Visual Binary
Stars can be distinguished using a telescope

Spectroscopic Binary
Analysis if its light spectrum shows 2 different classes of stars the wavelengths show a periodic splitting in frequency.

Eclipsing binary
Analysis of the brightness of its light spectrum shows periodic dips. This is because on star is in the way of the other.

Parsec
A unit of distance that is equal to 3.26 light years

Apparent magnitude
How bright a star appears from Earth.

Absolute magnitude
The apparent magnitude a star would have if it was 10 parsecs away.

Critical density
The theoretical density of the universe that would create a flat universe.

Hubble's Law
The recessional velocity of a galaxy ∝ its distance away from Earth.

Audible frequencies
2Hz  20KHz

(Sound) Intensity
Amount of energy that a sound wave brings to a unit area every second.

(Sound) Intensity Level
 10 lg (I / I0);
 where I0 = 1.0 × 1012 Wm2.

Attenuation Coefficient
The probability of a single photon being absorbed in 1 m of the material use defining equation.

Halfvalue thickness
The halfvalue thickness is that thickness of material which will reduce the intensity of the (transmitted) beam by 50%

Acoustic Impedance
The product of of the density of a substance and the speed of sound in that substance.

Exposure
The total ionized charge produced in unit mass of air by a particular radiation. Q=mX.

Absorbed Dose
The energy absorbed per unit mass of tissue. E=mD.

Quality Factor
This allows doses of different types of radiation to be compared for their biological effects.

Dose Equivalent
The amount of energy absorbed

Physical HalfLife
 The time it takes for the activity of a sample
 to halve.

Biological HalfLife
The time it takes the body to naturally eject half of an ingested sample of a radioactive isotope.