Physics - Definitions 2

Units, Quantities & Measurements Base Units: mass, distance, time, current, amount, temperature and light intensity. Derived Units: base units derived by multiplication or division. Prefixes: tera, giga, mega, kilo, deci, centi, milli, micro, nano, and pico. Homogenous: units on one side must be the same as on the other.

Vectors, Scalars & Linear Motion Vectors and Scalars: types of measurement you can make. Scalar Measurement: records the magnitude (or amount) of whatever you are measuring. Vector Measurement: records the magnitude of the thing you are measuring and the direction. Resultant Vector: single vector that has the same effect as all the others put together. Speed: rate of change of distance or the distance moved in unit time. Velocity: rate of change of displacement. Acceleration: how rapdily something is changing speed. Displacement: distance moved in a specified direction. Displacement-time Graph: shwos the motion of an object and allows you to find position and velocity at any time. Velocity-time Graphs: follow the same idea as displacement-time grpahs, velocity is on the y-axis.

Equations of Motion v: final velocity. u: initial velocity. a: constant acceleration. Projectiles: vectors at right angle to each other are independent; have no effect on each other.

Circular Motion Newton's First Law: if an object continues in straight line at http://education.helixated.com An Open Source Education Project

consatnt velocity, all forces acting on the object are balanced. Circular Motion: resultant force. Called the centripetal force. Centripetal Force: always directed towards the centre of the circle (along the radius of the circle). Centripetal Acceleration: caused by the centripetal force. Always at 90oM to the direction of the movement of the object. Angles: measured in degrees. 360o = 1 rotation. Radians: radius of a circle and its circumference are related by the equation: circumference = 2pr Angular Speed: measures the angle of a complete circle (measured in radians) covered per second.

Forces Force: rate of change of the linear momentum of a body. Balanced Forces: cause no acceleration. Unblanaced Forces: cause acceleration in the direction of the resultant force. Calculating Force: F = ma. F: force (N) m: mass (kg) a: acceleration (m/s2). Newton's First Law of Motion: bodies will continue to move with a uniform velocity unless acted on by a resultant force. Newton's Second Law of Motion:resultant force is equal to the rate of change or momentum. Newton's Third Law of Motion: every force has an equal and opposite force. Friction: caused by rubbing, Can be the surfaces between two solids rubbing, a solid surface and a liquid or a gas. "Friction Dissipates Energy": means that energy moves, usually changing from kinetic energy to heat energy, where it is lost ot the surroundings. Terminal Velocity: when air resistance force up has grown so big that it matches the weight down, there is no resultant force and therefore no acceleration. Pressure: caused by forces acting on a surface. http://education.helixated.com An Open Source Education Project

Momentum and Impulse Linear Momentum: p, defined as the mass, m, of an object multiplied by its velocity, v. p = mv. Conservation of a Momentum Principle: states that the total momentum of a system remains constant provided that no external force acts on the system. Conservation of an Energy Principle: states that energy cannot be created or destroyed only transformed from one form to another. Collision Tyes: perfectly elastic, perfectly inelastic and inelastic. Impulse: the product of the force and the perpendicular distance

Moments, Couples and Equilibrium Moment: a force multiplied by the perpendicular distance from th eline of action of the force to the pivot. Couples: two forces acting on a subject and the forces are parallel, in opposite directions, of equal size and not along the same line of action. Triangle of Forces: finds out if the forces acting on an object are in equlibrium. Centre of Gravity: point where all the mass seems to be concentrated.

Work, Energy and Efficiency Energy: 'the capacity of a body to do work' Work: what something does whenever it transfers energy from one form to another. Work Equation: work = force x distance moved in the firection of the force, or W = Fs. Kinetic Energy: 1/2 mv2. Stored energy. Kinetic energy stored in an object that is moving = amount of work done accelerating it to that speed. Potential Energy: Ep = P.E = mgh. Energy stored in objects, which have been lifted against a gravitational field. http://education.helixated.com An Open Source Education Project

Power: the rate at which you do work. Power - Work Done/ Time Taken.

Current, Charge and Voltage Charge: a particle with charge will experience a force in an electric field. Measured in coulombs, C. Electrical Charge: quantity of electricty flowing in a circuit when unit current flows for unit time. Conservation of Time: it is not possible to to destroy or create charge. Static Electricity: caused by the transfer of electrons from one object to another. Van de Graff Generator: uses friction to charge up a metal dome. Current: rate of flow of eletric charge. Current Electricty: moving charged particles. It is the rate of flow of charges. Voltage: amount of attracting or repelling you do is measured in volts, also called the potential difference (p.d. for short). Series Circuits: current the same all around the circuit and voltage is divided between the components in the circuit. Parallel Circuits: current divides to travel along each loop and voltage is the same across each loop. Conventional Current: flow of positive particles. Ammeter: measures current. Voltmeter: measures voltage. Drift Velocity: average speed the particle travels at along the conductor. Current Equation: I = vAnq. I: current (amps, A). v: drift velocity (m/s). A: cross-sectional area of the conductor (m2). n: charge density (m-3). This is the number if charge carriers that can move per m3. q: charge on each charge carrier (coulombs, C). Conductors: metals. Electrons in the outer layers of metal atoms are free to move from atom to atom. http://education.helixated.com An Open Source Education Project

Insulators: where static charge builds up. Coulomb: amount of charge flowing past a point in the circuit every second when a current of one ampere is flowing.

Resistance Resistance: more resistance, more energy needed to push the same number of electrons though part of the circuit. Measured in ohms, W. The Ohm: is that resistance which when a potential difference of one volt exists across the ends of the conductor results in a current of one ampere flowing in the conductor. Ohmmeter: finds the resistance of a component. Ohm's Law: current through a component is always proportional to the voltage across it. Ohmic Resistor: any resistor that obeys Ohm's Law. Non-Ohmic Resistor: any resistor that doesn't obey Ohm's Law. Conductance: G, tells how easy it is for a current to flow through something. Measured in siemens, S. Thermistors: reduce their resistance as temperature increases. Light-dependent Resistors: decrease their resistance when energy is given, but this time the energy needs to be given as light energy. Resistivity: ability of a material to conduct. Measured in ohm-meters (Wm). Resistance Factors: length, area, material and temperature. Conductivity: reverse of resistivity. Electro-motive Force: emf. Any device putting energy into a circuit. Potential Difference: between two points is the work done when unit charge flows between two points. Emf and pd: measure of voltage and measured in volts, V. Emf: amount of energy of any form that is changed into electrical energy per coulomb of charge. pd: amount of electrical energy that is changed into other http://education.helixated.com An Open Source Education Project

forms of energy per coulomb of charge. Emf Sources: cell, battery (a combination of cells), solar cell, generator, dynamo, and thermo couple. Power Supplies: deliver low voltages and higher currents, like a car battery; need to have a low internal battery. High-voltage Power Supplies: produce thousands of volts, have extremely high internal resistance to limit the current that would flow if there were an accidental short-circuit.

Kirchoff's Law and Potential Dividers Kirchoff's First Law: at any junction in a circuit, the sum of the currents arriving at the junction = the sum of the currents leaving the junction. Kirchoff's Second Law: in any loop (path) around a circuit, the sum of the emfs = the sum of the pds. Electrical Potential Energy: energy used up as charge flows around a circuit and turns it into other forms, such as heat and light. Potential: amount of energy that each coulomb of charge has still got stored, ready to use. Potential Dividers: used to find the emf of a cell.

Power and Energy Electrical Energy: measured in units of the kWhr. Energy: power x time. KWhr: kW x hr. Transformers: used to step-up the voltages from the power station to the power lines and to step-down the voltage from the power lines to people's homes.

Alternating Currents Direct Currents: cells produce currents that travel in the same direction all of the time. Alternating Currents: current that is constantly changing direction. It is normally sinusoidal. Frequency: number of cycles completed per second. Measured in Hertz (Hz). http://education.helixated.com An Open Source Education Project

Period: T, time taken to complete one cycle. Peak Values: maximum values at the crest or trough. Equivalent to the amplitude of a wave. RMS Values: are the d.c. equivalent of an a.c value.

Capacitors Capacitors: big plates of metal close to each other but not touching. The Farad: is that capacitance which when one coulomb of charge is stored in a capacitor results in an increase in potential of one volt. Charge Stored: directly proportional to the potential difference across the plates. Capacitance: charge stored per unit pd across the plates. Measured in farad, F. Rate of Removal: of charge is proportional to the amount of charge remaining. Time Constant, T: of a circuit has the value R.C and is the time taken for the charge on a capacitor to decrease to 1 /e of its initial value. R: resistance on the circuit (W). C: capacitance of the circuit (F).

Magnetic Fields Magnetic Field: region in which a particle with magnetic properties experiences a force, and in which a moving charge experiences a force. Permanent Magnets: are common and are made of iron, cobalt or nickel alloys. Lines of Flux: represent magnetic fields on a diagram. Gravitational Field Strength: force per unit mass at a point in a field. Gravitational Potential: at a point, the work done bringing a unit ,ass from it to the point. Uniform Field: region between the poles shows equally spaced parallel lines. Ä: means that conventional current is flowing though a wire into the page. Electric Field Strength: force per unit charge at a point in http://education.helixated.com An Open Source Education Project

the field. Electric Potential: work done bringing a unit positive charge from infinity to the point in the field. Potential Difference: between two points in an electric field is the work done per unit charge moved from point to point in the field. Neutral Points: when two fields coincide they may cancel each other out and produce points where the magnetic field strength is zero. Magnetic Flux Density: name of magnetic field strength, given the symbol 'B'. Magnetic Field Strength: force acting per unit current in a wire of unit length, which is perpendicular to the field. Measured in tesla, T. Tesla: magnetic flux density that produces a force of one newton when a current of one ampere flows in a wire of length one metre. Iron: good core for solenoids as it is easily magnetised and demagnetised. B µ I: strength of a magnetic field is directly proportional to the current flowing. Hall Probe: device, which finds the strength of a magnetic field.

Forces in Magnetic Fields Motor Effect: if a wire carrying a current is placed in a magnetic field a force is produced. Flemmings Left Hand Rule: used to get the direction of the force on a single chanrge travelling in a field. Second Finger: Conventional current. First Finger: Field direction. Thumb: Thrust or force direction.

Electromagnetic Induction Magnetic Flux, f: magnetic field strength, B, multiplied by area swept out by a conductor. f = BA. Flux: amount of magnetic field that you've swept through. Units: weber, Wb. Magnetic Flux Linkage, F: magnetic flux for a coil of n turns. Measured in weber and has the symbol F. http://education.helixated.com An Open Source Education Project

Faradays Law: emf induced is equal to the rate of change of magnetic flux linkage or the rate of flux cutting.

Lenz's Law Lenz's Law: emf that is induced will be set up so that it opposes whatever set it up. Left Hand Rule: generating a current not a force. Right Hand Rule: tells you in what direction a current is induced in a conductor moved through a magnetic field. Ek: source of the emf, transferred from one other energy into electrical energy.

Transformers and Rectification Transformers: can step a.a. electricity voltage up or down. Turns Role: if you change the number of turns in the coils, you change the induced emf. Diodes: only allow current to flow in one direction.

Simple Harmonic Motion and Damping Simple Harmonic Motion, SHM: oscillation in which the acceleration of the Time Period, T: time taken for an oscillation/revolution object to complete one full oscillation. Frequency, F: number of oscillation/revolutions in one second, and is measured in Hertz (Hz). Displacement: distance the particle has been moved from its equilibrium position. Amplitude: maximum displacement of the vibrating object from the equilibrium position. Angular Velocity: angle swept out per unit time by a radius of a circle. Critical Damping: damping required to make the oscillations stop in the quickest possible time without going past the equilibrium position. Natural Frequency, F0: frequency of un-damped oscillations in a system, which has been allowed to oscillate on its pwn. Wavelength: distance from any point on a wave to the sam http://education.helixated.com An Open Source Education Project

epoint on the next wave. Intensity: of a wave is power per unit area at right angles to the wave. Resonance: occur when natural frequency of a body is equal to the frequency of a periodic force applied to the body, resulting in large amplitude oscillations. Forced Frequency: frequency with which the periodic force is applied.

Reflection, Refraction and Polarisation Law of Reflection: angle of incidence = angle of reflection. Speed: frequency x wavelength Critical Angle: angle of incidence at which the angle of refraction is 90o Optical Fibres: uses TIR to send light pulse down glass fibres. Polarisation: transverse waves oscillations are made to occur in one plane only.

Diffraction Diffraction:a wave will diffract (spread out) as it goes through a gap or past an obstacle. Coherent Waves: are waves with a constant phase difference. Interference and Superposiition: when two waves meet they will interfere and superpose. Superposition: will occur whether waves are coherent or not.

Progressive Waves Mechanical Waves: any waves that move through a medium. Progressive Waves: distribute energy from a point source to a surrounding area. Tranverse Waves: vibrations are perpendicular to the wave motion. Longitudinal Waves: vibrations are parallel to the wave http://education.helixated.com An Open Source Education Project

motion. Diplacement: distance a particle moves from its central equilibrium position. Amplitude: maximum displacement from the central equilibrium position. Phase Angle: position along the wave, measured in degrees or radians. Speed of Wave: v = fl. f: frequency (Hz) I: wavelength (m). v: speed (m/s) Nodes: parts of the wave where the amplitude is always zero. Antinodes: halfway between the nodes, where the amplitude is at a maximum.

Electro-magnetic Waves Electromagnetic Spectrum Waves: all travel the same speed in a vacuum, can be reflected, refracted, diffracted and polarised and are tranverse waves. Gamma Rays: emitted during radioactive decay, causes cancer by damaging cells. X-rays: produced by firing electrons at a metal target, causes cancer by damaging cells. Ultraviolet: emitted by the sun, can cause skin cancer. Visible Light: emitted by the sun, intense light can damage your sight. Infra Red: emitted by hot objects and can burn. Micro-waves: produced by changing currents in a conductor. Radio-waves: produced by changing currents in a conductor.

Matter and Antimatter Matter Particless: neutron, proton and electron etc. Antimatter Particles: routinely created in a particle accelerators. Pressure: force acting perpendicular on unit cross-sectional http://education.helixated.com An Open Source Education Project

area of the surface. Brittle: material that can't deform plastically without breaking. Ductile: material that can undergo extensive plastic deformation without breaing. Stiff: material that strongly resists elastic deformation. Malleable: material that can be worked into different shapes. Annihilate: when a particle and its corresponding antiparticle meet they annihilate one another. Particle Accelerators: physicts use to explore matter on the smallest scale. Electron Gun: useful for producing electrons of relatively low energy for laboratory work. Linear Acellerators: (LINAC), the charged particles are accelerated in a straight line. Mass Spectrometer: determine the comparative masses of ionised atoms and, later, the relative abundance of isotopes.

Particle Classification and Interactions Particle Families: leptons and hadrons. Quarks: small particles in which neutrons and protons are composed of. Quark Types: up, down and strange. Charge (Q): conserved in all interactions. Baryons: assigned a Baryon number (B). Conserved in all instructions. Strangeness (S): property possessed by strange quarks. Conserved in all but weak interactions. Interactions: forces between fundamental particles on the smallest scale. Fundamental Interactions: gravitational, weak, electromagnetic and strong. Feynman Diagram: represents the exchange of a virtual photon between two electrons. Electron Capture: interaction between a proton and an electron. http://education.helixated.com An Open Source Education Project

Conservation Laws: in any interaction charge (Q), lepton number (L) and baryon number (B) are conserved.

Atomic Structure Plum Pudding Model: the atom was believed to consist of a positive material "pudding" with negative "plums" distributed throughout. Nucleon Number: number of protons + neutrons (also called mass number). Proton Number: also called atomc number as no two elements have the same number of protons. Atomic Notation: describes the number of particles in a given atom. Isotopes: atoms with the same proton number but different numbers of neitrons. Nuclear Equations: explain what happens in radioactive decay processes. Unstable Nuclei: emit alpha, beta or gamma radiation in order to become more stable.

Radioactivity Radioisotopes: isotopes of atoms that radioactive decay. Background Radiation: radiation around; produced by natural and unnatural sources such as rocks and soil. Cosmic Rays: high-speed particles freom outer space and the sun, which continusly bombard the Earth. Ionising RadiationVarieties: a, alpha particles, b beta particles and g particles. Electric Fields: seperate alpha, beta and gamma. Cloud and Bubble Chambers: early detecting devices of subattomic particles. Spark and Drift Chambers: modern detecting devices of subatomic particles.

Radioactive Decay Equations Activity: rate of decay (or number of disintegrated per second) of a substance. http://education.helixated.com An Open Source Education Project

Half-Life: time taken for half of the radoactive nuceli persent to decay or the time taken for the activity of a sample to halve. Decay Constant: fraction of the total number of nuceli present that will deacy in a unit time. Inverse Square Law: gives a measure of how the intensity of radiation falls off with distance from a source.

Nuclear Energy Mass: a solid form of energy. E = mc2: finds out how much energy will be released when you chnage mass into energy. E: energy released (J) m: mass defect (kg) c: speed of light (ms-1) Binding Energy: energy released when the nuceli is assembled from its constitutional parts. Nuclear Fusion: smaller nuclei combine (give out energy in doing so) to produce larger nuclei. Nuclear Fission: larger nuclei split up to produce smaller nuclei and give out energy in doing so. Moderator: used to slow the collision of neutrons. Thermal Neutrons: lower energy neutrons.

Deformation of Solids Breaking Stress: stress at which material breaks. Deformation: change of size (dimension) under the action of a force. Density (p): weight per unit volume (units: kgm-3). Elastic Behaviour: material exhibiting return to its original size and shape when forces deforming it are removed. Elastic Limit: a limit within which a material will regain its original shape after the deforming force is removed. Hooke's Law: law describing behaviour of elastic solids, force is proportional to extension. Hysteresis: phenomenon of lagging behind of any effect when forces acting on a body are changed. http://education.helixated.com An Open Source Education Project

Molecular Volume: Vmolecule, average volume occupied by each molecule in a substance. Molar Mass: mass of one mole of the material. Mole: amount of material containing 6.023 x 1023 molecules. Plastic Behaviour: behaviour of a material where deformation remains after the forces are removed Resilience: ability of a material to be repeatedly stressed without plastic deformation and without losing strength. Spring Constant: force per unit extension. Strain: extension per unit length. Strain Every Density (Pe): energy stored per unit volume in a material when elastically deformed. (Units: Jm-3). Stress: force per unit area of a material (Units: Nm-2 or Pa). Ultimate Tensile Strength (UTS): maximum tensile stress a material can stand. Yield: suddenly increased deformation. Young's Modulus (E): a constant indicating stiffness of a material. Given by the ratio: stress/strain (Units: Nm-2 or P).

Stress and Strain Stress: force per unit area of a material. Stress = force/cross sectional area. Strain: extension per unit length. Strain = extension/original length. Breaking Points: a material physically breaks at its breaking point. Density: weight per unit volume.

Temperature and Thermal Properties Centigrade Scale: measures the changes to a thermometric property of a substance in thermal equilibrium with the object. Fixed Points: value of the thermometric property when it is at two known temperatures. Thermodynamic Scale: straight-line relationship between temperature and the thermometric property. http://education.helixated.com An Open Source Education Project

Ek: (kinetic energy) component relates to the temperatures of the substance. Ep: (potential energy) component relates to the state of the substance. Specific Latent Heat: amount of energy per kg (unit mass) required to change ice to water. Specific Heat Capacity: thermal energy (heat) required to raise the temperature of unit mass by one kelvin or degree. Molar Heat Capacity: (of a gas) is the thermal energy (heat) required to raise the temp of one mole of an ideal gas by one kelvin or degree.

Thermodynamics and Ideal Gases Heat: if you heat up gas, you pass energy to the atoms (it appears as Ek). Work: we define work done by the gas pushing back its surrounding, as positive. p-V or Indicator Diagrams: graphs showing how pressure and volume vary when we do certain things to a gas.

Kinetic Energy Ek: vibration, rotation or translation of the atoms. Ep: is due to the interaction of one atom and its neighbours. Ideal Gases: one, which all its internal energy is in Ek. Brownian Motion: large numbers of particles moving in continuous random motion. Speed Term: average of the square speed, which has a different value from the square of the average speed. Root Mean Square: square root of the mean square speed. Boltzmann Constant: k, is the universal molar gas constant for 1 atom or molecule.

Quantum Physics Quantum Theory: light comes in packets of energy (photons). E = hf, each photon interacts with only one electrons (and vice versa). Work Function f: energy needed for an electron to leave the surface of the material. http://education.helixated.com An Open Source Education Project

Einstein's Photoelectric Equation: energy supplied = energy used for hf = F + ½ mv2max. Emitter: plate in which the photons first arrive. Collector: metal plate in which the electrons that cross the gap are collected. Cathode: name of the emitter as it gives out electrons.

Wave Particle Duality Wave Particle Duality: electrons, protons, a - particles can be diffracted. De Broglie Wavelength for Particles: l = hp p: momentum of the particle. E-M Radiation: propagates as a wave, interacts with surfaces as a particle. Electron Energy Levels: electrons can only exist in discrete energy levels. Electrons: jumping from low to high levels; absorb energy in lumps. Jumping from high to low levels; emit energy in lumps. Lumps Energy Calculation: hf = E1 - E2. Spectrum Lines: frequencies of light that exactly match the energy required to make the jumps between energy levels. Absorption Spectrum: dark lines on coloured background. Emission Spectrum: lines of colour on a dark background.

Electric Fields and Forces Electric Field: region which particles with charge experience a force. Electric Field Strength, E: force per unit charge acting at a point in the field. Radial Fields: formed around a point charge. Non-uniform field. Projectile Experience: constant horizontal velocity and constant vertical acceleration.

Electrical Potential Electric Potential: electrical potential energy per unit charge (i.e. per coulomb) at a point in a field. http://education.helixated.com An Open Source Education Project

Potential Definition: "the potential at a point in a field is equal to the work done per coulomb in moving a positively charged particle from infinity, to that point in the field." Equipotentials: points in the field of equal potential, and are at right angles to the field lines. Potential Gradient: rate of change of spacing between equipotentials.

Gravitational Fields and Forces Gravity: force that acts between any two masses. Gravitational Field: a region which masses will experience a force. Force in a Gravitational Field: F = M.g. Gravitational Potential Energy Gravitational Potential F: potential energy per kilogram at a point in a field. Potential F: at a point in a field is the potential energy per kg. Equipotential: points of equal potential in a field. Potential Gradient: rate of change of potential.

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