## Our Dynamic Universe

### Distance

### Scalar quantity - How far the object actually moved

### Displacement

### Vector quantity - How far is the End point from the Start

### Speed

### Scalar quantity - Distance / Time

### Velocity

### Vector quantity - Displacement / Time

### Angular Velocity

### The Rate of change of Angular displacement

### Tangential Velocity

### The Linear Velocity of an object traveling in a circle. It is the velocity with which the object would move if the Centripetal Force was removed.

### Acceleration

### "The Rate of Change of Velocity" or the "Change in Velocity per second"

### Angular Acceleration

### The Rate of Change of Angular Velocity.

### Radial Acceleration

### The Acceleration towards the Center of a Circular motion, caused by a Centripetal Force.

### Centripetal Force

### Force inwards towards the Centre of a Circular motion.

### Newton's First Law

### An object will remain at rest or travel with a constant Velocity unless acted on by an unbalanced Force

### Newton's Second Law

### The acceleration of an object is directly proportional to the unbalanced force and inversely proportional to its mass

### or

### F = ma

### Newton's Third Law

### If A exerts a force on B, then B exerts an equal but opposite force on A

### Torque

### The Turning Effect of a Force at a set distance from a pivot point, measured in Nm.

### Law of Conservation of Energy

### Energy can not be created or destroyed, only changed from one form into another

### Law of Conservation of Momentum

### In a collision where no external forces act, the total momentum before = the total momentum after

### Angular Momentum

### The product of the angular velocity of a rotating object and its moment of Inertia, measured in kgm^{2}s^{-1}.

### Law of Conservation of Angular Momentum

### In a collision where no external Torques act, the total angular momentum before = total angular momentum after.

### Elastic Collision

### Both Momentum and Kinetic energy are conserved

### Inelastic Collision

### Momentum is conserved, Kinetic Energy is NOT conserved

### Low Earth Orbit

### Orbital Period ~ 90 Minutes

### Mainly Used for Earth Observation Satellites

### Geostationary Orbit

### Orbital Period = 1 day

### For an Observer on the Earth, a Geostationary Satellite will appear stationary in the sky.

### Gravitational Field Strength

### The Force exerted upon a mass of 1 kg at a certain point within a Gravitational Field

### Gravitational Potential

### The Work Done by an external Force to bring a Unit Mass from infinity to that point.

### Gravitational Lensing

### The bending of Light around a massive object, caused by the light following a straight path through Curved Space-Time

### Escape Velocity

### The Minimum velocity required for an object to escape ( to infinity ) the Gravitational field of another object.

### Schwarzschild Radius

### The Distance from the centre of a Black hole at which the Escape Velocity is equal to the Speed of Light. Also known as the Event Horizon

### Singularity

### A 1-dimensional point of infinite density at the centre of a Black Hole

### Time Dilation

### ( Special Rel )

### The apparent increase in the length of 1 Second, caused by relative motion greater than 0.1 C. The consequence of this is that Time appears to run slower at relativistic speeds.

### Time Dilation

### ( General Rel )

### The apparent increase in the length of 1 second, caused by the proximity of an object with a large gravitational field strength.

### Length Contraction

### The apparent decrease in the length of 1 meter, caused by relative motion greater than 0.1 C. The Consequence of this is that objects appear shorter ( in the direction of travel) at relativistic speeds

### Worldline

### The Line on a Space-Time diagram showing an object's position within Space-Time.

### Protostar

### Cloud of Dust and Gas collapsing under Gravity, increasing in Temperature and Pressure ( No Fusion ) .

### Main-Sequence Star

### Star held in Gravitational Equilibrium, Inwards Gravitational Force balanced by the Outwards Thermal Pressure due to Hydrogen Fusion.

### Post Main-Sequence Star

### Hydrogen Fusion ends, final fate of the Star dependent on its original Mass.

### Black Body Object

### An object which perfectly absorbs and emits all frequencies of Electromagnetic radiation.

### Luminosity

### The Total Power a Star emits across all frequencies

### Doppler Effect

### Apparent change in the frequency of a Wave due to relative motion

### Red Shift

### Source Moving Away from Observer, Wavelength appears longer

### Blue Shift

### Source Moving Towards the Observer, Wavelength appears shorter

### Cosmic Microwave Background

### The observed background radiation that is present in every direction in the Universe, it provides strong evidence of the Big Bang

### Dark Energy

### Proposed type of Energy, used to account for the increasing rate of expansion of the Universe.

### Dark Matter

### Proposed type of Matter, used to account for "missing mass" within the Universe, it cannot be detected by conventional telescopes

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## Electricity

### Potential Difference ( V )

### Work done in transferring one coulomb of charge from one point to another

### Current

### Rate of Flow of Charge, measured in Amperes

### Current

### ( Electron Flow )

### Current Direction used in Scotland, shows the flow of Negative Charge Carriers moving from Negative to Positive

### Current

### ( Conventional )

### Current Direction used in rest of World + Engineering in Scotland, shows the flow of Charge Carriers from Positive to Negative.

### EMF

### The Energy given to each Coulomb of Charge passing through a Cell.

### Internal Resistance

### The resistance of the Cell itself. A Cell can be modelled as a source of EMF in series with an internal Resistor

### Lost Volts

### Energy used (by the internal resistance of a battery) by each coulomb of charge passing through the Cell

### Terminal Potential Difference

### The Voltage of a Cell or Battery as Measured across its terminals

### Direct Current

### Current ( and Voltage ) are in one direction only. An example of a DC supply is a Battery

### Alternating Current

### Current ( and Voltage ) continuously change direction. An example of an AC supply is Mains Electricity

### Peak Voltage or Current

### The highest value reached by an Alternating Voltage or Current

### RMS Voltage or Current

### The Average value of an Alternating Voltage or Current, causes heating equivalent to the DC Voltage or Current

### Electric Field Strength

### Force applied to unit charge (1 coulomb) in an electric field

### Coulomb's Law

### The Electrostatic Force between two point charges is proportional to the product of the two Charges, and inversely proportional to the square of the distance between them.

### Electric Potential

### The Work Done to move a Unit Positive Charge from Infinity to a point within an Electric Field.

### Capacitance

### ( F )

### The Number of Coulombs of charge stored per Volt

### Time Constant

### The Time Taken for a Capacitor to Charge to 63% of Full Charge, or Discharge to 37% of Full Charge. Can be found by the product of the Capacitance and the Resistance within the Circuit.

### Capacitive Reactance

### The Opposition to Current Flow in a circuit due to a Capacitor, measured in Ohms.

### Magnetic Domain

### A Region within a Ferromagnetic material where all atoms are aligned with their Magnetic Fields parallel to each other.

### Induced EMF

### The EMF generated in a conductor by a changing external Magnetic Field. The Induced EMF always acts to oppose the change which caused it, and therefore is also known as the Back EMF.

### Electromagnetic Induction

### The magnitude of the EMF produced is proportional to the rate of change of Magnetic Flux through the circuit.

### Self Inductance

### The generation of a Back EMF within a Coil due to the current flowing within it.

### Electron-Volt

### Equal to 1.6 x10^{-19} J. Defined as the Work Done to move a single Electron through a Potential Difference of 1 Volt.

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## Particles and Waves

### Baryon

### A Particle made of Three Quarks

### Meson

### A Particle made of Two Quarks ( Quark - Anti Quark Pair )

### Lepton

### A Fundamental Particle of Matter

### Boson

### A Force Mediating Particle

### Anti-Matter

### Every particle has an anti-particle. These are identical in every way, but carry the opposite charge. If they meet, they annihilate each other releasing Energy.

### Atomic Number

### The Number of Protons within the Nucleus of an Atom.

### Mass Number

### The Number of Nuclear Particles ( Protons + Neutrons ) within the Nucleus of an Atom.

### Alpha Decay

### Radioactive Emission of an Alpha Particle ( consisting of a Helium Nucleus ) from the Nucleus of an Atom.

### Alpha Decay decreases the Mass Number by 4 and the Atomic Number by 2.

### Beta Decay

### Radioactive Emission of a Beta Particle ( consisting of a High Energy Electron ) from the Nucleus of an Atom. Beta Decay does not change the Mass Number, but increases the Atomic Number by 1.

### Gamma Decay

### Radioactive Emission of a Gamma Ray from the Nucleus of an Atom. Gamma decay does not change either the Mass Number or the Atomic Number.

### Nuclear Fission

### A Large Atomic Nucleus is Split into two ( or more ) smaller Nuclei, releasing several Neutrons and Energy.

### Nuclear Fusion

### Two small Nuclei combine under high temperatures and pressures to form a larger Nucleus, releasing Energy.

### Simple Harmonic Motion

### The motion of an Object oscillating around a fixed equilibrium position. The acceleration of the Object is proportional to its displacement, and is always directed towards the equilibrium point.

### Travelling Wave

### A Wave in which Energy is transferred from one point to another by vibrations.

### Stationary Wave

### A Wave in which the points of zero and maximum displacement do not move through the medium.

### Node

### A point on a Standing wave where there is zero displacement. Occurs due to destructive interference between the incident and reflected wave.

### Damping

### A decrease in the amplitude of oscillations due to the loss of energy from the oscillating system, for example the loss of energy due to work against friction.

###

### Wavelength

### The distance between any two repeating points within a Wave, measured in Meters.

### Amplitude

### The vertical distance between the peak ( or trough ) of a wave and the Equilibrium Point.

### Period

### The Time Taken for One wave to Pass a point, measured in Seconds.

### Frequency

### The Number of Waves passing a point in One Second, measured in Hertz.

### Coherent Wave

### Coherent Waves have Same frequency, wavelength and speed and are in phase.

### Constructive Interference

### When 2 wave crests or 2 wave troughs arrive at the same point at the same time, they are said to be in phase, causing a Maximum. The superposition of these two waves results in a stronger signal.

### Destructive Interference

### When a wave crest and a wave trough arrive at the same point at the same time, they are said to be out of phase, causing a Minimum. The superposition of these two waves causes the signals to be cancel each other out.

### Optical Path Difference

### The Optical Path is equal to the product of the Physical Path Difference and the Refractive Index. Used when two rays pass through materials with different Refractive Indices before interfering.

### LASER

### Light Amplification by Stimulated Emission of Radiation, gives Monochromatic and coherent light

### Point Source

### A source which emits Electromagnetic Radiation equally in all directions.

### Irradiance

### The amount of Light Energy incident on every square metre of a surface per second.

### Work Function

### The minimum energy which must be supplied to by each Photon enable an electron to escape from a metal surface.

### Threshold Frequency

### The Minimum Frequency of a Photon required to cause an Electron to undergo Photoelectric Emission.

### Spontaneous Emission

### Light is emitted when electrons in an excited state drop to a lower energy level. Emitting photons in any direction, randomly.

### Stimulated Emission

### An incoming photon causes an electron to jump down to a lower energy level and emit a photon. The photons are in phase and moving parallel to each other in the same direction.

### Stimulated Absorption

### Incoming photons are absorbed by electrons in a lower energy level causing them to jump to a higher energy level.

### Unpolarised Light

### Light in which the Electric Field oscillations occur in random Planes.

### Optical Activity

### The effect of some materials of rotating the Plane of Polarisation of a Beam of Light passing through it.

### Polarised Light

### Light in which all Electric Field oscillations are in one Plane.

### Saccharimetry

### Technique that uses the Optical Activity of a Sugar solution to measure its concentration.

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## Miscellaneous

### Mains supply frequency - 50Hz

###

### Mains supply voltage - 230V

### Evidence for particle theory - Photoelectric effect

### Evidence for wave theory/ test for wave - Interference Patterns

### Dispersion using a prism - Red deviates least, Violet deviates most

###

### Interference diffraction grating - Red deviates most, Violet deviates least