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Physics Leaving Certificate Higher Level.Link revision to the type of questions that appear on the paper. Questions can be divided into three main categories.(1) Questions on definitions and laws of physics.(2)Mathematical type questions(3)Experimental type questions.Category 1Pay particular attention to words like Define, State etc. Definitions are exact statements and must be learned as such and written out in full. If asked for a statement of a law, an expression will suffice, provided that you indicate fully what each term in the expression represents. To revise for this type of question, write out all the laws and definitions on a separate sheet of paper for each topic and learn. Category 2This type of question needs practice and can be broken down into a number of steps.(a) recognising the information being supplied(b) using the relevant formulae(c) substituting the supplied data(d) solving the unknownIn order to answer a mathematical type question, one must know the relevant formula. Show the main steps involved in a calculation, do not produce an answer straight from a calculator because if it happens to be incorrect then one cannot receive any marks. Make sure that you are able to use your calculator, this may seem obvious but students make calculator errors every year. (Powers of 10, wrong mode for angular measurements etc.) One must include units with a numerical answer, a numerical answer without units is meaningless except in the case of a ratio. Failure to include a unit or having the incorrect unit will result in the loss of one mark. Each time an arithmetical error occurs in a calculation, one mark is deducted. For questions involving vectors make sure to include both the magnitude and the direction in your answer.Category 3:When describing experiments there are four steps to include(a)labelled diagram of apparatus(b)Method/procedure for carrying out the experiment / correction of errors in measurements(c)Mathematical equation / formulae required / construction of suitable graphConclusions / precautions.Practise drawing the diagrams and learn all of the four steps for each of the experiments on the course.Section A of the paper is based on the mandatory experiments. One will be supplied with sample results and will have to use the data to calculate a value for the required quantity. There are 24 mandatory experiments on the course (7 in mechanics, 4 in heat, 3 in sound, 5 in light and 5 in electricity) Four of these experiments will appear on the paper from which one must answer three so it is imperative that these experiments are well known. Pay particular attention to the wording “Draw a suitable graph on graph paper.” If the correct variables aren’t plotted then no marks will be obtained for the graph part of the question, failure to use graph paper will result in the deduction of all allotted marks other than those for correctly labelled axes and for prior calculations if required.When plotting a graph the following rules apply(a)graph should be plotted on graph paper(b)graph should be plotted in pencil(c)axes should be labelled, appropriate units displayed and suitable scales chosen.data points should be clearly visible When drawing a straight line graph it should be one of best fit, that is it should go through as many points as possible and for the points that do not lie on the line there should be equal distribution on either side of the line. When obtaining the slope of a line choose two non data points as far apart as possible and use the co-ordinate geometry slope formula.Allocation of time: (This is just a suggestion)Initial reading of paper and tidying up10 minutesSection A: three questions from four to be answered, (30% of total mark)15 minutes approximately per questionSection B: five questions from eight to be answered, (70% of total mark)25 minutes per question.Question five will consist of ten items, eight of which are to be answered. Answer in excess of eight and marks will be awarded for the best eight.Question twelve will consist of four parts of which two parts are to be answered.There is no compulsory question on the paper.At higher level the syllabus includes two options: Applied Electricity and Particle Physics. A question may be included to assess these options, if it does the candidate will only be expected to answer one option.There are fourteen official Department Examination Papers (2002-2015) and one Department Sample Paper (February 2002). There are also sample papers produced by some of the publishers. It would be worth trying questions from these sample papers. (Some unofficial papers may cover topics that are not on the syllabus).Light: reflection and refraction.Luminous object: one that gives out light.Transparent material: allows light to pass through and through which objects can be seenTranslucent material: allows light to pass through but through which objects cannot be clearly seen.Opaque material: one through which light cannot pass.Reflection: the bouncing of light off an object in its path.Diffuse reflection: reflection from a rough surface. A parallel beam of light incident on such a surface is reflected in all directions.Regular reflection: reflection from a smooth surface. A parallel beam of light incident on such a surface is reflected as a parallel beam. Laws of reflection of Light:The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.The angle of incidence is equal in size to the angle of reflection.Real image: This is formed by the actual intersection of rays, can be formed on a screen and is inverted.Virtual image: This is formed by the apparent intersection of rays, cannot be formed on a screen and is upright.Parallax: This is the apparent movement of objects relative to each other due to the movement of an observer.Refraction: This is the change of direction of a ray of light when it goes from one medium to another. (This happens for all wave types)Laws of refraction of light:The incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane.The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media.Sin i / sin r = n where n is a constant i is the angle of incidence, r is the angle of refractionn is the refractive index between the two media.Critical angle: This is the angle of incidence in the denser medium for which the angle of refraction is 90 in the less dense medium.Total internal reflection: When the angle of incidence in the denser medium exceeds the critical angle the light does not enter the second medium, it is reflected back into the denser first medium. Short sight: A short-sighted person can see nearby objects clearly but cannot bring distant objects into focus. The image of a distant object is formed in front of the retina. This defect is corrected using a concave lens.Long sight: A long-sighted person can see distant objects clearly but cannot bring nearby objects into focus. The image of nearby objects would be brought to a focus behind the retina. This defect is corrected using a convex lens. Experiments: (those in bold type are mandatory)To demonstrate the laws of reflection.To locate the image in a plane mirror.To measure the focal length of a concave mirror.To verify Snell’s Law and hence determine the refractive index of glass.To determine the refractive index of a transparent liquid.To measure the focal length of a convex lens.Constructions:Ray diagrams for concave and convex mirrors.Rotation of light through 90 and 180 using a 904545 prism.Ray diagrams for convex and concave lenses. Formulae:1f = 1u + 1vm= vun = real depthapparent depthn = speed of light in airspeed of light in second mediumn = 1Sin CThe power of a lens = 1focal length P = 1fP = P1 + P2MechanicsDisplacement: distance in a given direction.Velocity: The rate of change of displacement with respect to time. Speed in a given direction.Acceleration: the rate of change of velocity with respect to time.Vector quantity: A quantity that has both magnitude and direction.Scalar quantity: A quantity that has magnitude only.Force: Anything that causes the velocity of an object to change.Mass: The mass of a body is a measure of how difficult it is to accelerate that body. A measure of the amount of matter in the body.Momentum: The momentum of a body is the product of its mass and velocity.The newton: The force that would give a mass of 1 kg an acceleration of 1 ms-2.Weight: The weight of an object is the pull of gravity on it towards the centre of the earth. Newton’s Laws of Motion:1Every body will remain in a state of rest or of uniform motion in a straight line unless acted on by an external force.2The rate of change of momentum of a body is proportional to the applied force and takes place in the direction of the applied force.3For every action there is an equal but opposite reaction. The action and reaction occur on different bodies. If one body A exerts a force on a second body B then B exerts an equal and opposite force on A.Friction: This is the name given to the force that opposes the relative sliding motion between two bodies in contact.The Principle of conservation of momentum: When two bodies collide the total momentum before the collision is equal to the total momentum after the collision provided no external forces act. / For a closed system, the momentum before a collision is equal to the momentum after the collision.Density: The density of a body is the mass per unit volume.Pressure: the force per unit area.Archimedes Principle:This states that when a body is partially or totally immersed in a fluid, the upthrust it experiences / (apparent loss in weight) is equal to the weight of the displaced fluid.Law of flotation:This states that the weight of a floating body is equal to the weight of the fluid it displaces.Boyle’s Law: At constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure.Moment of a force: This is defined as the magnitude of the force multiplied by the perpendicular distance from the fulcrum to the line of action of the force.Lever: This is any rigid body that is free to turn about a fixed point called the fulcrum.Couple: a system of forces that produce a turning effect. Two parallel forces with the same magnitude acting in opposite directions is called a couple.Moment of a couple: This is equal to the product of one of the forces and the perpendicular distance between them. Conditions for equilibrium:The vector sum of the forces in any direction is zero.The sum of the moments about any point is zero.Work: work is done when a force act through a distance and the amount of work done is equal to the product of the force and the distance moved.Energy: This is the ability to do work.Joule: This is the amount of work done when a force of 1 newton moves its point of application through a distance of 1 metre.Principle of conservation of energy:Energy cannot be created or destroyed it can only be converted from one form to another.Power: this is the rate at which work is done. It is the rate at which energy is converted from one form to another.Angular velocity: The rate of change of angular displacement with respect to time. / The angle swept out in unit time.Centripetal acceleration: If a body is moving in a circle the acceleration it has is directed towards the centre of the circle and is called centripetal acceleration.Centripetal Force. This is the force required to keep a body moving in a circle and is always directed towards the centre of the circle.Newton’s Law of Gravitation:This states that the force of attraction between any two point masses is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.Hooke’s Law:This states that when an object is bent, stretched or compressed by a displacement s, the restoring force F is directly proportional to the displacement provided the elastic limit is not exceeded.Simple Harmonic Motion: A body is undergoing shm if(i) its acceleration is directly proportional to its distance from a fixed point and(ii) its acceleration is always directed towards that fixed point.Experiments: (mandatory experiments in bold type) Measurement of constant velocity.Measurement of constant acceleration.Measurement of the acceleration due to gravity g.Finding the resultant of two forces.To show that the acceleration of a body is directly proportional to the force acting on it. a FTo verify the principle of conservation of momentum.To demonstrate the principle of Archimedes.Demonstration of atmospheric pressure.To verify Boyle’s Law.To investigate the laws of equilibrium for a set of coplanar forces.Investigation of the relationship between period and length for a simple pendulum and hence calculate acceleration due to gravity g.Derivations: (these are examinable)Equations of motion , v = u + at, s = ut + 12 at2, v2 = u2 + 2as v = r?Derivation of the relationship between the period, the mass of the central body and the radius of orbit for satellite motion.Show that any system that obeys Hooke’s Law will execute shm.Formulae:Speed = distance timevelocity = displacementtimeacceleration = change in velocitytime v = u + at, s = ut + 12 at2, v2 = u2 + 2asPerpendicular components of vectors x = r Cos ??????????y = r Sin ?F= maW = mgmomentum = mvF = mv-mutFt = mv - mu? = mvP = FAP1V1 = P2V2F = GMmd2g = GMd2moment = force x perpendicular distanceW = F sKinetic energy = 12 mv2Potential energy = mghpower = WtPercentage efficiency = (Power output / Power Input ) x 100Angle in radians ??= srAngular velocity ?????θtLinear velocity v = r ?centripetal acceleration a = v2r, a = r ??centripetal force F = mv2r, F = m r ??v2 = GMRT = 2πRvT2 = 4π2R3GMHooke’s Law F = - ksSimple harmonic motion a = - ??s period T = 2πωPeriod T of a simple pendulum T = 2πlg Temperature and Heat:Temperature: a measure of hotness or coldness of a body.SI unit of temperature is the kelvin.Celsius Scale is the practical scale of Temperature.Heat: is a form of energy.Thermometric property: any physical property that changes measurably with temperaturelength of a column of liquidelectrical resistance (conductors, semiconductors)emf of a thermocouplecolour of crystalsvolume of a fixed mass of gas at constant pressurepressure of a fixed mass of gas at constant volumeHeat capacity: This is the amount of heat required to change the temperature of a body by 1 kelvin.Specific Heat Capacity: This is the amount of heat required to change the temperature of 1 kg of a substance by 1 kelvin.Latent Heat: the amount of heat required to change the state of a substance without a change in temperature.Specific Latent Heat: the amount of heat required to change the state of 1 kg of a substance without a change in temperature.Specific latent heat of fusion of ice: the amount of heat required to change 1 kg of ice to water at 0C.Specific latent heat of vaporisation of water: the amount of heat required to change 1 kg of water to steam at 100 C.Conduction: This is the movement of heat through a substance by the passing on of molecular vibrations from molecule to molecule. There is no overall movement of the substance.Convection: This is the transfer of heat through a fluid by circulating currents of the fluid called convection currents.Radiation: This is the transfer of heat energy by means of electromagnetic radiation and can take place in a vacuum. Travels in straight lines at the speed of light.U - Value: This is the amount of heat energy per second conducted through 1 m2 of a structure for every 1 kelvin temperature difference maintained between its ends. It is a measure of the conduction ability of a substance. A substance with a high u-value is a good conductor and a substance with a low u-value is a good insulator.Solar constant: This is the average amount of the sun’s energy falling per second perpendicularly on 1 m2 of the earth’s atmosphere. (Value of 1.37 kWm-2)Experiments: (bold type are mandatory)To illustrate the difference between heat and temperature.Demonstration of some thermometric properties.Use a thermometric property to measure temperature.To plot the calibration curve of a thermometer using the laboratory mercury thermometer as a standard.To measure the specific heat capacity of a liquid or a metal by a mechanical or electrical method. To measure the specific latent heat of fusion of ice. To measure the specific latent heat of vaporisation of water.To compare the rates of conduction through various solids.To demonstrate convection currents.To demonstrate properties of radiation with black and shiny surfaces.Formulae:Heat capacity H = mc???????????C??Latent heatH = mlt (degrees Celsius) = T (kelvin) - 273.15Specific Latent Heat of Fusion of iceHeat gained by ice melting + Heat gained by warming melted ice = Heat lost by water + Heat lost by cal. (ml)ice + (mc????icewater = (mc??? water + (mc???calSpecific Latent Heat of Fusion of WaterHeat lost by steam condensing + Heat lost by water at 100C = Heat gained by cold water + Heat gained by calorimeter.(ml)steam + (mc????steamwater = (mc??? water + (mc???calWaves, wave nature of light, Wave motion : This can be defined as a disturbance travelling through a medium by means of the periodic motion of the particles of the mediumTransverse waves: A transverse wave is one in which the direction of vibration of the particles of the medium is at right angles to the direction in which the wave is travelling.Longitudinal wave: A longitudinal wave is one in which the direction of vibration of the particles of the medium is parallel to the direction in which the wave is travelling.Wavelength: The distance between any two successive points on a wave moving in the same direction. (Distance from crest to crest or from trough to trough.)Amplitude: This is the maximum displacement of any particle of the medium from its mean position or undisturbed position. (Height of a crest or the depth of a trough.)Frequency: this is the number of waves passing any point per second.Periodic Time: this is the time for a wave to undergo one complete oscillation (time taken for any part of the wave to move forward one wavelength.Reflection: The bouncing of waves off an obstacle in their path.Refraction: The changing direction of a wave when it travels from one medium to another. This results because of a change in velocity.Diffraction. The sideways spreading of waves into the region beyond a gap or around an obstacle in its path is called diffraction.Interference: When waves from two different sources meet they combine and produce a new wave. The displacement of any point in the medium by this new wave is the algebraic sum of the displacements of the individual waves. This is called interference of waves.Constructive interference. When waves from two sources meet and the resultant amplitude is greater than the amplitude of each of the individual waves the waves are said to undergo constructive interference.Destructive interference. When waves from two sources meet and the resultant amplitude is less than the amplitude of each of the individual waves the waves are said to undergo destructive interference.Coherent sources: two sources of periodic waves are said to be coherent if they are in phase or there is a constant phase difference between them.Plane Polarisation: Waves are plane polarised when the vibrations occur in one plane only.Stationary wave: This is formed when two periodic travelling waves of the same frequency and amplitude moving in opposite directions meet and interfere with each other. The resulting wave is also called a standing wave.Doppler effect: This is the apparent change in the frequency of a wave due to the motion of the source of the wave or the observer.Dispersion: This is the separating of light into its constituent colours. This can be brought about using a prism or a diffraction grating.Primary colours: (light not pigments) Red, blue and green.Secondary colours: Colours obtained when any two primary colours are mixed.Electromagnetic spectrum: This is the full range of electromagnetic waves in order of increasing wavelength. Experiments: (those in bold type are mandatory)To demonstrate the wave nature of lightTo measure the wavelength of monochromatic light Constructions: Explanation of The Doppler Effect with accompanying diagramsFormulae:n? = d Sin?????????????nmax = dλElectricity:Insulator: a substance that electric charge cannot flow through easilyConductor: a substance that electric charge can flow through easilyCoulomb’s Law: This states that the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.Electric field: this is the region where a static electric charge experiences a force other than the force of gravity.Electric field line: This is the line in an electric field along which a positive charge will move if placed at that point in the field.Electric field strength: The electric field strength E at a point in an electric field is the force per unit charge at that point. This is also called the electric field intensity.Potential difference: The potential difference between two points in an electric field is the work done in bringing a charge of +1 coulomb from one point to the other.Volt: The potential difference between two points is 1 volt if 1 joule of work is done in bringing a charge of 1 C between them. Electric potential at a point: This is the amount of work done per coulomb in moving a charge from infinity to that point. The potential difference between the Earth and a point is called the potential of that point. (The Earth is taken to be at zero potential)Capacitance: The capacitance of a conductor is the ratio of the charge on the conductor to the potential difference across it.The Farad: A conductor has a capacitance of 1 farad if placing a charge of 1 C on it raises its potential by 1 volt.Electric current: this is a flow of charge.The size of an electric current in a conductor is defined as the amount of charge passing any point of the conductor in one second. In a metal the charge carriers are electrons.Ohm’s Law: This states that the potential difference across a conductor is directly proportional to the current flowing through it provided the temperature is kept constant.Resistance. The resistance of a conductor is the ratio of the potential difference across it to the current flowing through it.The ohm is the unit of resistance. A conductor has a resistance of 1 ohm if the current flowing through it is 1 amp when the potential difference across it is 1 volt.Resistivity: The resistivity of a substance is the resistance of a piece of the substance of length 1 m and of cross sectional area 1 m2.Joule’s Law: The rate at which heat is produced in a conductor is directly proportional to the square of the current provided its resistance is kept constant.Ion: This is a charged atom or a charged group of atoms. In an electrolyte the charge carriers are positive and negative ions.Kilowatt-hour: This is the amount of energy used by a 1000 W appliance operating for 1 hour.Semiconductor: A material whose resistivity is between that of a good conductor and a good insulator. The resistivity of a semiconductor decreases with increasing temperature.The charge carriers in a semiconductor are positive holes and negative electrons.Intrinsic conduction: This is the conduction in a pure semiconductor due to the electrons moving in one direction and an equal number of holes moving in the opposite direction under the influence of an applied electric field.Extrinsic conduction: This is the conduction in a doped semiconductor, the majority carriers in n - type material are electrons and the majority carriers in p - type material are holes.n- type semiconductor. This is a semiconductor that has impurities added to increase the number of free electrons available for conduction. (Impurity atoms from group 5 )p - type semiconductor: this is a semiconductor that has impurities added to increase the number of holes available for conduction. (impurity atoms added from group 3 )p - n junction: This is a piece of semiconductor with an abrupt change from p - type to n - type material.Depletion Layer: The region at both sides of a p - n junction in which there are no free majority carriers. This region acts like an insulator and the potential difference that exists across this region is called the junction voltage.Experiments/demonstrations: (bold type are mandatory)Charging by friction and showing like charges repel and unlike charges attract.Charging by inductionUses of the gold leaf electroscopeTo show charge distribution on a conductorTo show that all static charge resides on the outside of a conductorTo show electric field patternsTo show that a charged capacitor stores energyTo investigate the factors which determine the capacitance of a parallel plate capacitorTo demonstrate Ohm’s LawTo investigate the variation of the resistance of a metallic conductor with temperatureTo investigate the variation of the resistance of a thermistor with temperatureTo measure the resistivity of the material of a wire. Measure resistance using a metre bridgeVerification of Joule’s Law To demonstrate the chemical effect of an electric currentTo investigate the variation of current with potential difference fora metallic conductor a filament bulbcopper sulphate with copper electrodesa semiconductor diode. Formulae:F= Q1Q24πε0d2 ?r = εε0E = FQ E = Q4πεd2W = Q VC = QVC = εAdE = ? CV2E = Q22CQ = ItP = V IVI = RResistors in series R = R1 + R2 + R3 (to be derived)Resistors in parallel 1R = 1R1 + 1R2 + 1R3 (to be derived)R = ?ρlA ????RAlWheatstone bridge R1R2 = R3R4H = R I2 tP = R I2Magnetism:Main properties of a bar magnet:Attracts ferromagnetic materials to it.Is strongest at each end.If freely suspended it will line up in a north south direction.Like poles repel, unlike poles attract.Magnetic field: This is the region around the magnet where the magnetic force can be felt. The direction of the field at any point is the direction of the force on a north pole at that point.Magnetic field line: This is the line along which an isolated north pole would travel if placed at that point in the magnetic field.Right Hand Grip Rule: This states that if a current carrying conductor is held in the right hand with the thumb pointing in the direction of the current, then the direction of the magnetic field is given by the direction of the fingers.Angle of declination: This is the angle between the geographic north pole and the magnetic north pole at a point on the earth’s surface.Fleming’s Left Hand Rule: This states that if the thumb, first finger and second finger of the left hand are held at right angles to each other with the first finger pointing in the direction of the magnetic field and the second finger pointing in the direction of the current then the thumb will point in the direction of the force.Magnetic flux density (B): The magnetic flux density at a point in a magnetic field is a vector whose magnitude is equal to the force that would be experienced by a conductor of length 1 m carrying a current of 1 A when placed at right angles to the field at that point and the direction of the vector would be the direction of the force on a north pole placed at that point. F = BilSinThe Tesla: The magnetic flux density at a point is 1 tesla if a conductor of length 1m carrying a current of 1A experiences a force of 1N when placed at right angles to the field at that point.The Ampere. The ampere is that constant current which if maintained in two infinitely long straight parallel conductors of negligible cross sectional area, placed 1m apart in a vacuum would produce a force on each conductor of 2 x 10-7 N per metre of length.Experiments/demonstrations: To plot the magnetic field of a bar magnetTo show the magnetic effect of an electric current (discovered by Oersted)To plot the magnetic field due to the current in a straight wireTo plot the magnetic field due to a solenoidTo demonstrate the force on a current carrying conductor when placed in a magnetic fieldTo show the magnetic force between two current carrying conductorsFormulae:F = B i l Sin ? F = B q v (this formula to be derived.)Electromagnetic Induction:Whenever there is a changing magnetic flux linking a coil there is an induced emf in the coil. This phenomenon is called electromagnetic induction. Magnetic flux: The magnetic flux through an area A is equal to the magnetic flux density multiplied by the area. = BAIf the magnetic flux density is not perpendicular to the area then the magnetic flux through A is the component of B that is perpendicular to the area multiplied by the area. =BASinweber (Wb): This is the unit of magnetic flux.The weber: The magnetic flux through an area of 1m2 is 1 Wb if the magnetic flux density is 1 T.Faraday’s Law of electromagnetic Induction: This states that whenever there is a changing magnetic flux linking a conductor there is an induced emf and the size of the induced emf is directly proportional to the rate of change of flux linking the circuit.Lenz’s Law: This states that the direction of the induced current is always such as to oppose the change that caused it.Electrical Generator: This is a device that converts mechanical energy to electrical energy.Mutual Induction: If a changing magnetic field in one coil induces an emf in another coil.Self induction: This is when a changing magnetic field in a coil induces an emf in the coil itself.A coil will oppose the flow of direct current with its ohmic resistance but a coil will oppose the flow of alternating current with both its ohmic resistance and the back emf induced in it as a result of self induction.Transformer: This is a device that is used to change the value of an alternating voltage.Experiments / Demonstrations:Demonstration of the principle of electromagnetic inductionDemonstration of Faraday’s Law of electromagnetic inductionDemonstration of Lenz’s Law of electromagnetic inductionUse of oscilloscope to show a.parison of peak and rms values of a.c.Demonstration of mutual inductionDemonstration of self inductionDemonstration of a.c. and inductors.Demonstration of transformer.Formulae: = BA = BA Sin E = - N ( / t) E = (final flux – initial flux) / time taken I r m s = Ip / 2Vr m s = Vp / 2 P r m s = I r m s x V r m s Vi / Vo = Np / Ns The Electron, Thermionic Emission, Photoelectric Effect, X-Rays:Negatively charged particle that orbits the nucleus.Name proposed by Irish Physicist G. J. Stoney.Very small mass 9.1 x 10-31 kgIndivisible quantity of charge, measured by American Robert Millikan in 1911. e = 1.6 x 10-19 CThermionic emission: This is the emission of electrons from a hot metal surface.Cathode Ray Tube: consists of a heated filament, cathode, anode, fluorescent screen, deflection plate or deflection coils.Cathode Rays: These are streams of high speed electrons.Properties of cathode rays:Travel from cathode in straight linesCan be deflected in electric and magnetic fieldsCause certain substances to fluoresceCan produce x- rays when they strike heavy metal targetsCan cause photoelectric emission.The electronvolt eV: This is the energy gained or lost by an electron when it is accelerated through a potential difference of one volt.1eV = 1.6 x 10-19 JApplications of a cathode ray tube:Cathode Ray OscilloscopeTelevision / computer monitor tubeElectrocardiogram ECGElectroeccephalogram EEGPhotoelectric Effect: This is the emission of electrons from the surface of a metal when electromagnetic radiation of a suitable frequency is incident on it.Threshold Frequency: This is the minimum frequency below which photoelectric emission will not take place for a given metal. Only electromagnetic radiation above this frequency will result in photoemission.Threshold Wavelength: This is the maximum wavelength above which photoelectric emission will not take place for a given metal. Only electromagnetic radiation below this wavelength will result in photoemission.Work Function: The work function of a metal is the minimum amount of energy needed to remove the most loosely bound electron from the surface of that metal.Photon: This is a packet of electromagnetic energy whose energy is given by E = hf where f is the frequency and h is Planck’s constant.The photoelectric effect produced some surprising results.(i) Electrons were emitted when light fell on the metal(ii) Number of electrons emitted depended on the intensity of the light falling on the metal.(iii) The energy of the emitted electrons depended on the frequency of the light falling on the metal not on the intensity.(iv) No electrons were emitted for light below a certain frequency.(i), (iii) and (iv) cannot be explained if light is a wave motion. A wave should give up its energy across the wave front; all the electrons on the surface of the metal should share this energy. The wave theory would say that the energy of a wave depended on the amplitude so the energy of the emitted electrons should have depended on the intensity of the light and not the frequency. The wave theory of light could offer no reason as to why there should be a threshold frequency.Max Planck when studying black body radiation had proposed that radiation was not emitted or absorbed continuously but in packets or bundles of energy. Einstein extended Planck’s Theory to explain the photoelectric effect. He said that for an electron to be emitted from a metal a certain minimum amount of energy was needed. The incoming photon (packet of energy) had an energy given by E = hf. This energy was given to a single electron. If the incoming photon had this minimum energy then the electron was released. If it didn’t then electrons would not be released irrespective of the number of incoming photons. Any excess energy carried by the incoming photon will be given to the electron in the form of kinetic energy.Energy of incoming photon = Energy to release the electron + kinetic energy of released electron.X-Rays: These are high frequency electromagnetic radiation produced when high speed electrons strike a heavy metal target.Properties of x-rays: Electromagnetic radiation with wavelengths between 10-9 to 10-15 mHighly ionisingHighly penetratingNot deflected by electric or magnetic fieldsCan cause photoelectric emissionDisplay interference and diffraction effectsCause fluorescence in certain materialsBlacken photographic plates.Principle of operation of the hot cathode x-ray tube:Emission of electrons occurs at the hot cathode The electrons are accelerated across the tube by the high voltage between the cathode and the anode.When the electrons strike the heavy metal target, electrons are knocked out of inner shells. Electrons from higher shells drop down to take their place but in order to do so they have to lose some energy. This is achieved by emitting the excess energy as electromagnetic radiation i.e. x-rays.Most of the energy of the incident electrons appear as heat, thus the metal target must have a high melting point, may be sloped to provide a larger target area to the incident beam and may be rotated. Furthermore the target may be cooled by circulating water.The tube is shielded by lead except for a small exiting window for the x-rays. Penetrating power of the x-rays: This is determined by the frequency of the x-ray which is determined by the voltage across the tube. Very penetrating x-rays are called hard x-rays and less penetrating x-rays are called soft x-rays.The intensity of x-rays: This is determined by the number of x-rays being produced which is dependent on the temperature of the heated cathode.X-ray production as the inverse of the Photoelectric effect: In the photoelectric effect electromagnetic radiation strikes a metal and the energy is transferred to electrons which are then emitted. In x-ray production high speed electrons strike a metal target, they lose their energy and electromagnetic radiation is emitted. Experiments / Demonstrations:Demonstration of the photoelectric effect using zinc plate, gold leaf electroscope and different light sources.Demonstration of the action of a photocell. The photo current is directly proportional to the intensity of the light falling on it. Formulae:? mv2 = eVW = QVF = qvBmv2r = eVI 1d2E = hf = hc? mv2 max = hf – hf0? mv2 max = hc – hcλ0The Nucleus, Radioactivity and Nuclear Energy.Line emission spectrum: This consists of a series of coloured lines on a dark background. It is given out by gases in the atomic state.Continuous spectrum: This consists of a continuous band of colours from red to violet. It is produced by solids and liquidsEnergy Level: This is defined as the fixed energy value that an electron in an atom may have.Atomic Number: The Atomic Number (Z) of an element is the number of protons in the nucleus of an atom of that element.Mass Number: The Mass Number (A) of an element is the number of protons and neutrons in the nucleus of an atom of that element.Isotopes: Isotopes of an element are atoms of that element that have the same atomic number but a different mass number. Atoms of the element that have the same number of protons but a different number of neutrons.Radioactivity: This is the spontaneous disintegration or decay of the nuclei of certain atoms with the emission of one or more types of radiation. (alpha, beta or gamma emission)Alpha () radiation: This consists of high speed helium nuclei emitted from the nucleus of radioactive atoms.Beta () radiation: This consists of high speed electrons emitted from the nuclei of radioactive atoms.Gamma () radiation: This consists of high frequency radiation emitted from the nuclei of radioactive atoms.Law of radioactive decay: The number of nuclei decaying per second is directly proportional to the number of nuclei undecayed.Half-Life: The half-life of a radioactive isotope is the time taken for half of the undecayed nuclei to undergo decay.Half-Life: The half-life of a radioactive isotope is the time taken for its activity to decrease by one half.Becquerel (Bq): This is the unit of activity and is defined as one disintegration per second.Mole: A mole of a substance is its molecular mass expressed in grams.Mole: A mole of a substance is that quantity of the substance that contains Avogadro’s number of particles.Nuclear Fission: This is the splitting up of a large nucleus into two smaller nuclei of roughly the same size along with the release of neutrons and energy.Chain reaction: The progressive disintegration of fissile material by bombardment with neutrons, which in turn results in the production of more neutrons which under suitable conditions produce further fissions.Critical mass: The minimum mass of material that can sustain a nuclear chain reaction. This depends on the purity of the sample.Nuclear Fusion: This is the joining of two small nuclei to give a larger nucleus along with the emission of energy.Experiments: Principle of Rutherford’s gold foil scattering experimentAll the positive charge and mass of atom concentrated at the centre. Most of the atom consists of empty space. Diameter of nucleus 10,000 times smaller than diameter of atom.Demonstration of line spectra and continuous spectraDemonstration of penetrating power of , and radiationDemonstration of ionising power of , and radiationDemonstration of a detector of radiation.Principle of operation of a detector of ionising radiationMeasurement of background radiationFormulaeRadius of nucleus 10-15 m ; Radius of atom 10-10 mE2 – E1= hf Rate of decay = N ; A = N ; δNδt= NT? = ln2λ = 0.693/ E = mc2Bohr model of atom.Electrons revolve around the nucleus in fixed paths called orbitsElectrons in an orbit have a fixed amount of energyElectrons normally occupy the lowest energy levelsWhen an electron absorbs energy it jumps to a higher energy level. An atom in this state is said to be excited.When an electron drops back to a lower energy level the energy difference between the two levels is emitted as a photon of light or electromagnetic radiation. Since the photon has a definite amount of energy it has a definite wavelength and will appear in a spectrum as an individual line of a definite colour.The energy of the light is given by E2 – E1= hf = hcλ where E2 and E1 are the initial and final energies of the electron.Properties of particles: Helium nucleus, deflected by electric and magnetic fields, mass of 4 units, positively charged +2, strongly ionising, weakly penetrating, cause fluorescence and blacken photographic plates.Properties of particles:High speed electrons, deflected by electric and magnetic fields, rest mass of 0, negatively charged –1, moderately ionising, moderately penetrating, cause fluorescence and blacken photographic plates.Properties of radiation:High frequency electromagnetic radiation, not deflected by electric or magnetic fields, rest mass 0, uncharged, weakly ionising, strongly penetrating, travel at the speed of light, cause fluorescence and blacken photographic plates.Changes in Mass number and Atomic number due to radioactive decay:If an particle is emitted the mass number decreases by 4 and the atomic number decreases by 2. If a particle is emitted the mass number remains the same and the atomic number is increased by 1.If a ray is emitted the mass number remains the same and the atomic number remains the same. Nuclear Reactor: Fuel: Natural uranium or enriched uraniumControl Rod: Rods of neutron absorbing materials that can be moved into or out of the nuclear reactor to control the chain reaction. Made of boron or cadmium or other substances that absorb neutrons.Moderator: Materials used in the core of nuclear reactors to slow down fast-moving neutrons so that they will cause fission in the fissile material. Graphite, heavy water, paraffin wax and beryllium are possible moderator materials.Coolant: A fluid that removes heat from the core. Carbon dioxide is a suitable material.Heat exchanger: A device for transferring heat from one fluid to another.Shielding: Stops radiation escaping. Concrete is a suitable material.Environmental Impact of fission reactors:The release of radon gas around uranium mines.Containment of radioactive material within the reactor.Removal and treatment of spent fuel rodsStorage of radioactive waste.Advantages of fusion reactors:No radioactive wastes.Plentiful supply of deuterium from the oceans.Health Hazards of ionising radiation:High doses of ionising radiation (cosmic radiation, X-rays and , and radiation from radioactive materials) cause chemical and biological changes in human cells. This can result in various forms of cancer. The effect of the radiation depends onThe type of radiationThe activity of the sourceThe duration of exposureThe type of tissue irradiated ................
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