Glossary

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 kgm2s-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