AQA AS Physics unit one

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AQA AS Physics unit one
2014-04-20 05:40:29
unit one

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  1. accurate
    when a reading is very close to the true value
  2. alpha particle
    a particle consisting of two neutrons and two protons tightly bound together , as in a helium nucleus , emitted as strongly ionising short range radiation by some unstable isotopes
  3. alternating current
    current produced when charges oscillate back and fourth , rather than drifting in one direction
  4. annihilation
    when particles of matter and antimatter , such as an electron and positron  , collide and are destroyed and their mass converted to energy
  5. antimatter
    the term used to describe matter composed of antiparticles ; it is created by high energy collisions or decays but exists in only small amounts in the observable universe
  6. antiparticle
    a particle of identical mass to a more common particle , but which has opposite values of charge , baryon number and strangeness , denoted by a bar over the symbol
  7. atomic number
    the number of protons in the nucleus , also called the proton number ; has the symbol Z
  8. baryon
    any particle composed of three quarks
  9. baryon number
    a number  ,denoted by the symbol B , assigned to a particle as a consequence of its quark structure : baryons have B=1 , anti baryons have B=-1 and all other particles have B=0
  10. beta minus particle
    a fast moving electron emitted from the nucleus of some unstable isotopes as a result of a neutron decaying into a proton
  11. beta plus particle 
    a fast moving positron emitted from the nucleus of some unstable isotopes as a result of a proton decaying into neutron 
  12. black body radiator 
    a body that absorbs all the radiation incident upon it and reflects none , i.e. it is a perfect emitter and perfect absorber ; the surface temperature determines how much energy it emits at each wavelength 
  13. gauge boson 
    a particle , also called a an exchange particle , that carriers the force between two particles ; for example the photon is a gauge bosons that carriers the electromagnetic force 
  14. cathode 
    the negative terminal of a power supply , or a negative electrode 
  15. charge mass ratio
    the charge carried by a particle divided by its mass , also called the specific charge , unit CKg-1
  16. conductor
    a material that allows electric current to pass through it ; it has a low electrical resistivity 
  17. conservation laws 
    certain physical quantities remain the same for any closed system , and these are said to be conserved quantities ; during particle interactions , charge , baryon number and strangeness are conserved : the total value of each of these quantities is the same before and after any interaction 
  18. control variable 
     a variable that is not of interest in an experiment but which may have an impact on the results and so needs to be controlled (fixed) 
  19. conventional current 
    the direction of electric current is taken to be the way that positive charge moves : this is known as conventional current ; in metallic conductors it is in fact negative charges (electrons) that move , in the opposite direction to the conventional current 
  20. critical temperature 
    the temperature below which a material becomes superconducting and its electrical resistance drops to below zero 
  21. current 
    electrical current , I , is the charge , Q , which passes a point in a given time interval , delta t : I = delta Q / delta t ; unit A
  22. de Broglie wavelength 
    the wavelength of a particle when it behaves like a wave ; it depends on the particles momentum , p : wavelength = h/p where h is the Planck constant 
  23. dependant variable 
    the variable that changes when the independent variable in an experiment is changed 
  24. diode
    a semi conductor device that allows current to flow in one direction only 
  25. direct current , dc ,
    current produced when charges drift in a steady direction 
  26. elastic scattering 
    when particles collide elastically , i.e. when the total kinetic energy of the particles involved in the collision is conserved 
  27. electromagnetic wave 
    a wave that propagates by transferring energy between electric and magnetic fields ; does not need a medium in which to travel ; light is an electromagnetic wave 
  28. electromotive force (e.m.f)
    the energy transferred by a power source to each coulomb of charge ; equal to the potential difference at the terminals of the source when no current is flowing , unit V
  29. electron 
    a fundamental particle , a member of the lepton family , carries a negative charge of 1.6 x 10-19C and has a mass of 9.11 x 10-31Kg 
  30. electron volt (eV)
    a unit of energy equal to the energy transferred when an electron moves through a potential difference of 1 volt 
  31. enegry
    the ability to do work , where work is defined as a force moving through distance , for example lifting a weight 
  32. energy level 
    specific allowed energy values of electrons in an atom 
  33. exchange particle 
    a particle that mediates the force between two particles , also known as a gauge boson 
  34. excitation 
    the process of raising to a higher energy level , for example by collision with a free electron or by the absorption of a photon 
  35. femtometre (fm)
    unit of length , typical of nuclear dimensions , equal to 10-15
  36. Feynman diagram
    a representation of the exchange of particles in an interaction 
  37. fluorescence 
    the emission of light when excited atoms drop to a lower energy level 
  38. forward biased 
    a diode connected so that potential difference across it allows it to conduct 
  39. frequency 
    the number of oscillations or waves in line second 
  40. gauge boson 
    a particle , also called an exchange particle , that carries the force between two particles for example the photon is the gauge boson that carries the electromagnetic force 
  41. gluon 
    the gauge boson that carries the strong nuclear force
  42. gravitation 
    the gauge boson that carries the force of gravity 
  43. grond state
    an atom in its ground state has all its electrons in their lowest possible energy level it cannot emit any photons 
  44. hadron 
    a particle composed of quarks ; hadrons are divided into two subgroups mesons and baryons 
  45. hypothesis 
    a tentative (provisional) idea or theory to explain an observation 
  46. independent variable 
    the variable that is deliberately altered by an experimenter 
  47. inelastic scattering 
    when particles collide and there is a loss of kinetic energy ; if an electron is scattered inelastically by an atom , the kinetic energy it looses excites or ionises the atom , inelastic scattering may be followed by photon emission from the excited atom 
  48. insulator 
    a material with hardly any free electrons , which therefor has a very high electrical resistance 
  49. internal resistance 
    the intrinsic electrical resistance between the terminals of a power supply ; some energy is always lost inside the supply due to the internal resistance 
  50. ionisation 
    when an atomic electron gains enough energy to escape from the atom ; ionisation may follow a collision with a free electron or the absorption of a photon 
  51. isotope
    isotopes are different forms of atoms of the same element that have the same number of protons and electrons but different numbers of neutrons ; they are chemically identical but have different mass numbers 
  52. k meson - kaon
    • a meson with unusual decay and interaction properties that carries the conserved quantity , strangeness , there are four types :
    • k+ composed of an up quark and an anti strange quark 
    • k- composed of an anti up quark and and strange quark 
    • kcomposed of a down quark and anti strange quark 
    • -
    • k0 composed of an anti down quark and strange quark 
  53. lepton 
    one of a family of fundamental particles , the electron , muon , tau-particle and neutrino are all leptons 
  54. line spectrum 
    the light from a low pressure gas , which is emitted at a series of discrete wavelengths , seen through a diffraction grating as sharp lines of different colour , each element has its own characteristic line spectrum 
  55. longitudinal wave 
    a wave in which the oscillations are parallel to the direction of propagation (travel) of the wave , sound travels as a longitudinal wave 
  56. meson 
    a type of hadron formed from a quark and antiquark pair 
  57. muon 
    a fundamental particle in the lepton family that carries the same charge as the electron , but is about 200 times massive 
  58. nanometre (nm)
    unit of length , useful for wavelengths of visible light m equal to 10-9
  59. neutrino 
    a particle in the lepton family that has a very small mass and no charge ; there a three types , the electron neutrino , the muon neutrino and tau neutrino ; they interact only very weakly with other matter 
  60. neutron 
    a hadron of zero charge found in the nucleus of all atoms (except hydrogen -1) ; free neutrons are unstable and decay into protons by beta minus decay 
  61. neutron number
    the number of neutrons , N , in a nucleus N=A-Z
  62. nucleon 
    any particle ( a proton or neutron) that exists in the atomic nucleus 
  63. nucleus 
    the positively charged , dense matter at the centre of every atom , formed from a combination of neutrons and protons 
  64. nucleon number
    the total number of protons and neutrons in a nucleus , also referred to as the mass number ; symbol A 
  65. ohms law
    the current , I , through a material is proportional to the potential difference , V , across it ; this holds only for certain conductors in certain conditions
  66. ohmic conductor 
    a material that follows ohms law e.g. a metal at constant temperature 
  67. oscilloscope 
    a lab instrument (a very high resistance voltmeter) which shows on a screen how the potential difference between two points changes with time ; can be used to measure the peak voltage and frequency of ac signals 
  68. peak value 
    the maximum value (current or pd) of an ac signal , usually measured from zero ; peak voltage is written as V0 and peak current as I0
  69. pair production 
    the creation of a particle and its antiparticle from energy ; the opposite of annihilation 
  70. peak to peak value 
    the difference between the maximum positive and maximum negative values (current or voltage) of an ac signal , for a symmetrical wave the peak to peak value is twice the peak value 
  71. period 
    the time taken , T , for one complete oscillation or wave ; the reciprocal of the frequency , f : T = 1/f 
  72. photoelectric effect 
    the emission of electrons from a metal surface caused by illuminating the metal with electromagnetic radiation 
  73. photon 
    • 1) a quantum of electromagnetic energy  ; the energy , E , of a photon is given by E=hf , where h is the planck constant and f is the frequency of the electromagnetic radiation 
    • 2) the boson that carries the electromagnetic interaction 
  74. pi meson (pion) 
    • a meson (a hadron formed from a quark antiquark pair) there are three types : 
    •               + or - or 0
    • the + is composed of an up quark and an anti down quark 
    • the - composed of an anti up and a down quark 
    • the 0 is composed of an up quark and an anti up quark , or a down quark and anti down quark 
  75. positron 
    the electrons antiparticle ; it has the same mass as an electron and carries equal but opposite (positive) charge 
  76. potential difference p.d.
    the energy transferred per unit charge (1C) moving between two points ; unit V 
  77. potential divider 
    an arrangement of resistors in series so the pd across the combination is divided between them in the ratio of the resistors 
  78. power 
    the rate at which energ , E , is transferred : Power = delta E / delta t ; sometimes expressed as work done per second W = Js-1
  79. precise 
    when a reading can reliably be given to several significant figures 
  80. proton 
    a positively charge hadron composed of three quarks : up , up and down ; it is believed to be the only stable hadron 
  81. prediction 
    a forecast (from a hypothesis or theory) that can be tested by experiment 
  82. quantum 
    a discrete amount of a physical quantity , such as energy or charge ; for example charge cannot take any value but has to be a multiple of the charge carried by an electron : charge is said to be quantised 
  83. proton number 
    the number or protons in a nucleus , also called the atomic number ; has the symbol Z 
  84. quark
    a fundamental particle that is not observed in isolation but always in a combination of three (to make a baryon) or two (a quark antiquark pair to make a meson) ; quarks have a baryon number of 1/3 and they carry a fractional charge (+or - 2/3 or +or - 1/3 of the charge of an electron)
  85. resistance 
    a measure of how difficult it is for electric current to pass through an object ; it is the ratio of potential difference , V , to current , I , resistance , R , = V/I ; unit ohm 
  86. resistivity
    a property of a material that describes how difficult it is for current to pass through it ; for a conducting wire it is related to the resistance , R , the cross sectional area , A , and the length , l , by the formula ; resistivity p = RA/l ; unit ohm metre 
  87. rest energy 
    the energy of a stationary particle , Ewhen it is measured by an observer in the same frame of reference ; it is linked to rest mass , m0 , by the equation E= m0c2
  88. reverse biased 
    a diode connected so that the potential difference across it doesn't allow it to conduct 
  89. root mean square value rms 
    • the value of an a.c. current or potential difference that is equal to the dc value that would lead to the same power being dissipated in a resistor ; the rms values of I and V are linked to the peak values ; Irms = I0/root 2
    • and Vrms = V0/root 2 
  90. specific charge 
    the charge mass ratio of a particle ; unit CKg-1
  91. strangeness 
    a conserved , quantised quantity carried by the strange quark , which has strangeness S = -1 
  92. strong interaction 
    the strong nuclear force which acts between quarks and so acts between a lll hadrons ; it has a short range about 10-15m
  93. superconductor
    a conductor that has zero resistance at a temperature below its critical value
  94. tau
    the heaviest member of the lepton family ; it carries an identical charge to the electron but is 3500 times more massive
  95. thermionic emission
    the process by which electrons are released from the surface of a heated metal
  96. thermistor
    a semiconductor device whose electrical resistance changes significantly with temperature , used a heat sensor
  97. threshold frequency
    the lowest frequency of electromagnetic radiation that causes photon emission from the surface of a given metal
  98. time base
    the control on an oscilloscope that determines the speed at which the electron beam moves horizontally across the screen
  99. transverse wave
    a wave in which the oscillations are at right angles to the direction of propagation (travel) of the wave ; waves on a string , surface waves on water and electromagnetic waves are all transverse
  100. virtual particle
    the short lived exchange particle (gauss boson) that mediates interactions between particles
  101. wavelength
    the distance between identical points on consecutive waves ; symbol lambda
  102. wave particle duality
    the phenomenon of particles of matter , e.g. electrons , demonstrating both particle and wave properties
  103. weak interaction
    a fundamental force that acts between all particles over a very short range , 10-18m ; it is responsible for radioactive beta decay
  104. work function
    the minimum energy required to remove an electron from the surface of metal in the photoelectric effect
  105. x-plates
    charged plates used to deflect the electron beam in an oscilloscope in the horizontal direction
  106. y-plates
    charged plates used to deflect the electron beam in an oscilloscope in the vertical direction
  107. the electron was first identified during
    experiments using electrical discharge tubes.
  108. when the voltage is turned on , the screen at the end of the tube emits a glow . the glow was said to be caused by
    cathode rays .
  109. when the rays hit the screen , their energy is converted into
    light . this energy conversion known as fluorescence , is aided by coating the inside of the screen with a phosphor such as since sulphide
  110. draw an electrical discharge tube
  111. in 1897 jj Thompson discovered that he could
    deflect the rays using electric or magnetic fields .
  112. he balanced the two deflections so that the rays moved in a straight line . this allowed him to calculate
    the charge mass ratio of the particles making up the rays .
  113. he concluded that the cathode rays were
    tiny negatively charged particles now called electrons
  114. draw electrostatic and magnetic deflection of cathode rays and explain whats happening
  115. electrons are emitted from
    the negative electrode or cathode
  116. more electrons are emitted if
    the cathode is heated this is known as thermionic emission
  117. after they are emitted the electrons
    accelerate towards the anode finally hitting the screen , where they cause fluorescence
  118. Thompson realised that
    the electrons were torn away from atoms in the cathode's surface by the electric field . he suggested that atoms were composed of many electrons , moving in various orbits inside a positively charged cloud . this model of atom structure is often called the plum pudding model of the atoms
  119. properties of the electron
    • mass of the electron me = 9.1 x 10-31kg charge of the electron e = 1.6 x 10-19C charge mass ratio e/me = 1.76 x 1011 Ckg-1
  120. the plum pudding model had to be abandoned following
    Rutherford's scattering experiments . these showed that atoms were almost empty space but with a very small , very dense positively charged nucleus
  121. in our present model  , all the positive charge of the atom and nearly all of the mass are located in
    the central nucleus . Tiny negatively charged electrons orbit this nucleus , rather like planets orbiting the sun
  122. protons are the particles that carry
    the positive charge in the nucleus
  123. in a neutral atom , this is an atom with no net charge , the number of protons in the nucleus is
    balanced by the number of electrons orbiting the nucleus
  124. a hydrogen atom has ... proton and ... electron
    • 1
    • 1
  125. helium has ... protons and ... electrons and so on through the periodic table , until the heaviest naturally occurring element , .... , which has .... protons and ... electrons
    • 2
    • 2
    • uranium 
    • 92
    • 92
  126. what holds the nucleus together ? positive charges repel each other and at such short distances the electrostatic forces pushing the nucleus apart are very large . another force acts inside the nucleus known as the
    strong nuclear force or strong interaction
  127. the strong nuclear force has a very short
    range , it has no effect at separations greater than about 5fm (5 x 10-15m) .
  128. the strong nuclear force is is an attractive force until
    the separation is less than 1fm , when the force becomes strongly repulsive
  129. the overall effect of the string nucleus force is to
    pull the nucleus together , but the repulsive action prevents it from collapsing to a point
  130. for a large nuclei there is a problem . the strong nuclear force acts over a short range compared to the electrostatic attraction . It isn't possible to
    get all the protons together for the strong nuclear force to overcome the electrostatic repulsion . there has to be some other particle in the nucleus that helps to glue it all together and keep it stable . this is the neutron discovered by Chadwick in 1932
  131. draw a force distance graph for strong nuclear force without electrostatic repulsion
  132. the neutron is a particle with a
    mass almost identical to that of the proton , but with no electrical charge
  133. the neutron exerts a
    strong nuclear attraction on protons and on other neutrons
  134. protons and neutrons are the only
    particles in the nucleus . they are often referred to as nucleons
  135. the strong nuclear force acts between any pair of
    nucleons , whether that is two protons , two neutrons or a proton and neutron
  136. electrostatic repulsion acts only between
  137. draw a table to show the properties of protons , neutrons and electrons
  138. geiger and marsden , working in rutherfords labs at manchester uni in 1909 studied
    the scattering of alpha particles as they passed through a tho piece of gold foil . alpha particles are relatively massive , positively charged particles emitted by some radioactive materials
  139. alpha particles are
    two protons and two neutrons bound tightly together , the same configuration as a helium nucleus . an alpha particle therefor carriers a positive charge which is twice the size of an electron . the mass of an alpha  particle is about 800 times the electrons mass
  140. draw a diagram to show geiger and marsden's apparatus
  141. what did geiger and marsden use to detect the alpha particles
    a scintillator which was observed through a small microscope in a darkened room
  142. whats a scintillator
    a zinc sulphide screen which emits light whenever and alpha particle strikes it
  143. what did geiger and marsden expect to see
    the alpha particles deflected by small angles
  144. rurtherford suggested to move the detector in front of the foil to see if any alpha particles were bounced from the surface of the foil
    amazingly some were about 1 in every 8000 alphas were reflected or scattered through an angle of more than 900
  145. as an alpha particle travelling at around         10 000 km s-1 couldn't be bounced back by a positively charged cloud with tiny electrons in it , rutherford concluded that
    almost all the mass of the atom must be gathered together in one small volume , which he called the nucleus . he suggested that the electrons carry all the negative charge and that they orbit the nucleus through empty space a relatively long way from the nucleus
  146. most of the alpha particles passed through the gold foil with
    small or zero deflections because they were too far away from the nucleus to be affected from it . very occasionally an alpha particle would pass so close to the nucleus that it would be repelled by its positive charge and suffer a large deflection
  147. draw a diagram of rutherford scattering
  148. analysis of the results allowed rutherford to
    work out the scale of the nuclear atom . whereas the radius of the atom was about 10-10m , the nucleus was only about 10-15m across
  149. remember that the density , p , is defined as
    the mass in a unit volume : p = m/v and is measured in kg m-3
  150. all nuclei have approx the same density around
    2x1017kgm-3 , a matchbox full of nuclear matter would have a mass of around 8 billion tonnes
  151. the simplest atom is
  152. hydrogen has
    one proton and its nucleus has 0 neutrons . it has one electron orbiting the nucleus
  153. helium has
    two protons and and two neutrons in its nucleus , with two electrons in orbit around it
  154. draw a diagram to show the hydrogen and helium atoms
  155. the proton number or atomic number is
    the number of protons in the nucleus and is given the symbol Z
  156. the atomic number is also
    the number of electrons in the neutral atom . this determines the chemical properties of the atom . the atomic number is used to place numbers in the periodic table
  157. the nucleon number A is
    the total number of nucleons in the nucleus of an atom . it is also known as the mass number
  158. the neutron number N is
    the number of neutrons in the nucleus
  159. the mass number A is always
    a whole number
  160. the nucleon number is the number of protons plus the number of neutrons so A =
    Z + N
  161. the nuclear composition of an atom can be described using symbols . the most common form of carbon has six protons and 6 neutrons in its nucleus it can be written as
  162. the upper number is the
    nucleon number
  163. the lower number is the
    atomic number
  164. in general an element X with atomic number Z and atomic mass number A is written
  165. hydrogen usually has
    one proton only in its nucleus , but some atoms have one or two neutrons as well . the different atoms are referred to as isotopes
  166. isotopes are
    forms of an element with different numbers of neutrons but the same proton number
  167. the different isotopes of an element have
    identical chemical behaviour because their atoms have the same number of electrons . isotopes also have the same number of protons in their nucleus
  168. the difference is simply in the number of neutrons . this makes
    some isotopes heavier than others
  169. An antiparticle is
    A mirror image of a particle of identical mass but opposite charge
  170. The first antiparticle was discovered by Anderson in 1932 , who was observing
    Tracks in a cloud chamber made by cosmic rays . He used a strong magnetic field to curve the paths of high energy electrons . Some tracks seemed identical to the tracks but curved in the opposite direction . These were tracks of an anti-electron now known as a positron . This was an example of antimatter
  171. the positron is
    • The electRon's antiparticle 
  172. When a particle meets an antiparticle
    Particles are drawn together byelectrostatic attraction   until they annihilate each other
  173. Annihilation is
    the conversion of the mass of a particle and its antiparticle to a pair of photons of electroMagnetic radiation
  174. annihilation is an example of
    Mass energy equivalence as predicted by Einstein's special theory of relativity . The total mass energy in any system is conserved , but energy and mass may be converted from one to the other . Conversion of mass to energy powers radioactivity and nuclear fission
  175. Draw a diagram to show positron annihilation
  176. When a positron and electron meet
    They annihilate each other , two identical gamma rays of energy 511 KeV are emitted in opposite directions
  177. Annihilation is the conversion of matter to energy . The opposite process
    Where matter is created frOm energy is called pair production
  178. Pair pair production is
    The process in which a photon of electromagnetic energy is converted into a pair of particles
  179. In pair production there are always two particles created
    One is a conventional particle and the other is its antiparticle . This satisfies the conservation of charge , since before the event there is only a photoN of radiation which carries no charge . After the pair production there are always two particles of opposite charge , making the total charge zero
  180. A gamma ray has to have a minimum energy of
    1.02 MeV of before it can create an electron Positron pair .
  181. This is because
    The mass of the pair has an energy equivalent to 1.02 MeV
  182. If the photon has more energy than this
    The surplus energy appears as kinetic energy carried by the positRon and electRon
  183. IN 1955 the first nucleon was discovered
    Protons were accelerated to an energy of up to 6 MeV and collided into other protons in a stationary Target
  184. The two protons collided and produced
    • Antiprotons by the the reaction
    • p + p ---> p + p + p + antipRoton
  185. The joule is the
    SI unit of energy but it is too large for measuring energy on an atomic scale
  186. We can use the
    Electron volt (eV) a much smaller unit
  187. How many J = 1 eV
    1.6 x 10-19 J
  188. 1 eV is
    The energy Change when the charge on one electron passes through a potential difference of  1 V
  189. 1 KeV =
    1 000 eV
  190. 1 MeV
    1 000 000 eV
  191. 1 GeV
    109 eV
  192. 1 TeV
    1012 eV
  193. Draw a diagram of pair production.
  194. By colliding two protons together we have
    Produced an extra proton and an antiproton
  195. the extra mass needed to Create the proton antiproton pair has come from
    the kinetic energy of the initial protons
  196. A year later the antineutron was produced by using
    • Antiprotons to collide with protons 
    • Proton + antiproton --> n + antineutron
  197. Particles cannot be created unless
    There is enough energy
  198. The minimum energy needed to create a particle is known as
    Its rest energy E0
  199. Rest energy depends on
    Rest masS M0
  200. The rest energy is calculated from the rest mass using the formula
    • E= m0c2
    • Where c = the speed of light 
  201. What is the speed of light
    • 3*10ms-1
  202. An antiparticle is denoted by a
    Horizontal line above the symbol for the particle . The exception to this is the positron e+
  203. The rest mass of a particle is
    The mass when measured in a frame of reference where the mass is stationary . Einstein's special theory of relativity describes how the mass of an object increases as it moves faster
  204. Neutrinos are probably the most
    Numerous particles in the universe
  205. The neutrinos and antineutrinos are really difficult to
  206. neutrinos aren't
  207. This means that they
    Interact with matter very weakly
  208. Experiments to find neutrinos often use large tanks of water , usually placed deep underground surrounded by sensitive light detectors looking for
    The occasional flash of light that signifies a neutrino has interacted with a neutron , or an antineutrino or with a proton
  209. An antiparticle has the same mass as its conventional twin but opposite charge . What about the antineutron , which has no charge
    An antineutron has magnetic properties which are opposite to those of the of the neutron . It is more difficult to specify the difference between a neutrino and an antineutrino
  210. beta particles are
    Fast moving electrons
  211. Alpha particles are emitted with a
    Well defined energy
  212. Beta particles are emitted
    With a range of energies
  213. This seemed to contravene the principle of conservation of energy . of a certain amount of energy is transferred by radioactive decay
    Why did the emitted beta particle have a range of possible energies . Pauli suggested that another particle the neutrino carries away the balance of the energy , so that the total energy of the decay is always constant
  214. Draw a diagram to show the typical alpha spectrum and typical beta spectrum
  215. the neutrino is represented by the symbol
    • Ve 
  216. The subscript e stands for
    Electron ; these neutrinos are more properly referred to as electron neutrinos , because other tYpes of neutrino exist
  217. Beta particles are electrons emitted when
    A neutron decays into a Proton and an electron
  218. The proton stays inside the nucleus but
    The electron is emitted at high speed together with an antineutrino 

  219. Some radioactive decays emit a positive beta particle or a positron . This involves the
    • Decay of a proton into a neutron and can be written 
  220. The neutrino is a
    Fundamental particle which carries no charge . For some years it was believed to have zero mass but experiments now suggest that it has a small mass , much less than an electron
  221. The neutrino is a
    fundamental particle with no charge . It has a very small mass . It interacts with other mass very weakly
  222. Alpha particles tend to be emitted from
    Large unstable nuclei
  223. An alpha particle is
    Two protons and two neutrons bound Together . It escapes from the large nucleus leaving a different nucleus behind
  224. Draw a table to summarise the properties of the fundamental particles and their antiparticles
  225. the wave theory of light is extremely successful in explaining certain phenomena such as
    Diffraction and refraction
  226. However there are some Phenomena such as
    Black body radiation and the photoelectric effects Which cannot be explained assuming that electromagnetic radiation is composed of waves
  227. All objects emit radiation because of their
    Thermal energy
  228. The spectrum of radiation that is emitted depends on the
    Surface temperature of the object and on the type of Surface
  229. Objects which are ideal radiators of energy are know as
    Black body radiators
  230. A perfect black body is an
    Object that absorbs all the radiation that falls on it and reflects nOne . If this body is in thermal equilibrium with its surroundings then it must emit radiation at the same rate it absorbs it . A perfect black body is therefor an ideal radiator
  231. Draw a diagram to show black body radiation curves
  232. The wave theory of radiation couldn't explain the shape of the black body radiation
    In fact the wave theory predicted that at high temperatures infinite amounts of energy would be emitted at short wavelengths
  233. In 1909 max plank was able to explain the black body curves by suggesting
    That the energy was emitted intermittently in packets called quanta of energy . radiating body may emit an integral number of these packets of energy say one , two , three but cannot emit any fractional amount
  234. The amount of energy E carried by each quantum depends on the
    • Frequency , f , of the oscillations that are causing the radiation E ∞ f or E=hf
    • where h is the plank constant , which has a value of 6.63 * 10-34 js .
  235. The packets or quanta of electromagnetic energy are known as
  236. The electromagnetic force is carried between charged particles by the
    Photon . When two charged particles exert a force on each other a virtual photon is exchanged between them .
  237. The photon is a
    massless chargeless particle
  238. Draw a feynMann diagram showing two electrons feeling the electric force as a result of exchange of a photon
  239. The Feynman diagram represents
    The interaction between the particles . The angles of the particle paths are not significant but time is usually shown going up the page
  240. According to the uncertainty principle , particles (exchange particles) of energy E can be created for a time t provided that
    That the product Et is less than h
  241. The uncertainty principle allows particles
    to appear for a short tome before being annihilated again provided that Et < h
  242. The exchange particle for the strong interaction moving at close to the speed of light has to exist for
    about 10-23 s if it is to have time to travel across the nucleus . This enabled Yukawa to predict  a mass for the particle . The particle was discovered in 47 and was known as pi meson or pion
  243. The uncertainty principle is one of the key ideas of quantum physics . Although it seems odd with common sense , the theory is in excellent agreement with experimental results . It means that
    What we used to image as a vacuum is not composed of nothing at all ; rather there is constant creation and and destruction of virtual particle antiparticle pairs
  244. Draw a Feynman diagram showing pion exchange
  245. At a deeper level the strong interaction is mediated by gauge bosons called
    Gluons that pass between quarks
  246. The pion is simply a vehicle carrying
    Gluons between hadrons . There are eight different gluons , none of which has ever been detected as an individual particle , though scattering experiments have given a strong indication that the theory is correct
  247. The weak interaction has a very short range . This suggests that
    Its gauge bosons are relatively massive , since a large mass I.e. A high energy , would mean. Short lifetime and therefor exchange particles could only travel a small distance
  248. The weak interaction has three gauge bosons
    • Known as the intermediate vector bosons 
    • W+
    • -
  249. The weak interaction acts on
    • Leptons and in hadrons
    • it is the only force other than gravity which acts on neutrinos . This explains the fact that neutrinos are so reluctant to interact with anything
  250. radioactive beta decay is due to
    The weak interaction
  251. Beta minus decay
    A neutron decays into a proton emitting an electron and an antineutrino . The decay occurs via the weak interaction and is mediated by a W- boson
  252. Draw a Feynman diagram to show beta minus decay
  253. Beta plus decay (positron)
    A proton decays into a neutron , emitting an electron neutrino and a positron . The decay occurs via the weak interaction and is mediated by a Wboson
  254. Draw a Feynman diAgram to show beta plus decay
  255. Electron capture
    An atomic electron can be absorbed by a proTon in the nucleus in a process called electron capture . The decay occurs via the weak interaction and is meditated by a Wboson
  256. Draw a Feynman Diagram to show electron capture
  257. Electron proton collisions
    An electron can collide with a proton emitting a neutron and an electron neutrino . The reaction occurs via the weak interaction as Is mediated by a wboson  
  258. Draw a Feynman diagram to show electron proton collisions
  259. The gauge boson which carries the gravitational force is named the
    Gravitation . Its predicted to have Zero rest mass and zero charge . It has never been detected
  260. leptons are
    fundamental particles ; theu have no internal structure and aren't affected by the strong interaction
  261. how many different particles are there in the lepton family
  262. the most familiar lepton is the
  263. what two other particles are similar to the electron but massive
    tau and muon each of which have an associated neutrino . all these particles have an antiparticle of opposite charge
  264. how was the muon discovered
    in cosmic ray studies . it carries the same charge as the electron but is about 207 times more massive
  265. the neutrinos that carry accompany muons aren't the same as
    electron neutrinos
  266. the muon neutrino and its antiparticle are also
    fundamental particles which carry no charge
  267. how was the tau minus particle discovered
    by a team working on electron positron collisions
  268. the taut particle has
    the same charge as the electron but is 3500 times more massive . this lepton has its own type of neutrino and antineutrino
  269. draw a table to show properties of leptons
  270. leptons a summary :
    • the leptons and their antiparticles , anti leptons , are believed to be fundamental particles 
    • there are three negatively charged leptons : the electron , the taut and the muon particle 
    • each of these leptons has an associated neutrino 
    • leptons are not affected by the strong interaction
  271. in addition to the leptons the particles now known as pi mesons , kaons and delta mesons have much larger masses than the electrons and are known as
  272. all hadrons are said to be
    unstable except the proton
  273. all hadrons eventually decay into a
  274. the neutron decays with a half life of about 11 by
    • emitting a beta particle
  275. the hadrons themselves are divided into two groups
    • mesons 
    • baryons
  276. the baryons which were originally thought to be the heavier group include
    protons and neutrons and their antiparticles
  277. the mesons include a large number of particles originally found in
    cosmic rays , which are now commonly created in collisions inside particle accelerators
  278. which meson was first discovered
  279. the pion exists in three different forms
    • positively charged
    • negatively charged 
    • and uncharged
  280. many other mesons have since been discovered , all of them
    unstable , usually with very short lifetimes
  281. a large number of hadron have been studied . it became apparent that some
    reactions that appeared to be possible never took place . it seemed that some reactions were forbidden . we now know that there are some physical quantities which can't change in a reaction . these conserved quantities govern which reactions can occur
  282. one of the rules that governs the interactions between particles is the
    conservation of charge . no reactions that contravene this rule have ever been observed
  283. the conservation of charge means
    the total charge before a reaction must be the same as the total charge after a reaction
  284. there are some reactions allowed by conservation of charge that have never been observed this is because
    there are other conservation laws that place restrictions on which reactions that take place . one of these is the conservation of baryon number
  285. hadrons can be classified by baryon number into
    • baryons 
    • antibaryons 
    • mesons
  286. whats the baryon number of anti baryons
  287. whats the baryon number of baryons
  288. whats the baryon number of mesons
  289. reactions between any of these hadrons can only occur if
    the baryon number is conserved , just like charge , total baryon number before and after the reaction must be the same
  290. all other particles i.e. the leptons and gauges bosons have a baryon number of
  291. draw a table to show the baryon number for some hadrons
  292. the rules of conservation of charge and baryon number don't
    fully explain why some reactions are never observed
  293. kaons caused problems for physicists studying particles
    kaons appeared as the decay products of some neutral particles but always seemed to turn up in pairs . Kaons didn't appear individually , although charge and baryon number didn't prevent this . they also had a long lifetime about 10-10 s compared with other hadrons which had a typical lifetimes of 10-23 s
  294. there is another property that has to be conserved in hadrons reactions
    this property is called strangeness
  295. all hadrons are given a strangeness number of
    • +-1 
    • +- 2
    • +-3 
    • 0
  296. strangeness has to be conserved in any reaction that takes place via
    the strong interaction
  297. unlike charge and conservation of baryon number , there are some reactions where strangeness is not conserved these are decays that take place
    via the weak interaction
  298. draw a table to show the strangeness s for some hadrons
  299. draw a table to show particle interactions and conservation of strangeness
  300. all hadrons have fixed values for
    • charge Q
    • baryon number B
    • strangeness S
    • a reaction between hadrons can only take place if the reaction conserves these numbers
  301. when strange particles , i.e. those with non zero values of strangeness , are produced they have to
    appear in pairs to conserve strangeness .
  302. when they decay however
    they do do by the weak interaction and strangeness isn't conserved . in these reactions strangeness changes by +- 1
  303. the Stanford linear acceleration centre in California could accelerate electrons to an energy of around 6 GeV , high enough to probe the structure of nucleons , i.e. to look inside protons and neutrons . the experiments found that a
    significant proportion of high energy electrons were scattered through a large angle . this indicated that the neutrons and protons are not particles of uniform density but have point like charges within them
  304. draw a diagram to shoe electron scattering by quarks within a baryon
  305. Gell Mann had grouped the hadrons together in families . the patterns could be explained by
    supposing that all hadrons were composed of smaller constituents named quarks . the SLAC experiments confirmed that hadrons aren't fundamental particles but are composed of combinations of different types of quark
  306. draw a diagram to show the eightfold way
  307. mann suggested that there were 3 different quarks labelled
    • up - u 
    • down - d
    • strange - s
  308. each of these quakes has a particular mass and values for charge , baryon number and strangeness , each quark has a corresponding antiquark of exactly equal mass but opposite values for charge baryon number and strangeness , draw a table to show these properties
  309. using the quake model it is possible to describe all hadrons in terms of quarks and antiquarks . baryons are
    combinations of three quarks
  310. anti baryons are a combination of
    three antiquarks
  311. mesons are a
    composed of an antiquark and quark
  312. draw a diagram to show the quark composition of the proton , k + meson , neutron and pi - meson
  313. the properties of each hadron can be explained in terms of
    the quarks that it is made from
  314. the total charge on the hadron is equal to
    the sum of the quake charges
  315. draw a table to show the quark structure of the proton
  316. draw a table to show the quark structure of an antiproton
  317. draw a table to show the quark structure of a neutron
  318. draw a table to show the quark structure of an antineutron
  319. draw a table to show the quake structure of a pi - meson
  320. draw a table to show the quark structure of a K + meson
  321. draw a diagram to show pions and kaons in the simple quark model
  322. the quake model has been very useful in describing and predicting the properties of hadrons . in beta minus emission for example
    a nuetron decays into a proton emitting an electron and antineutrino in the process . the quark process theory tells us that inside the neutron a down quark has changed into an up quark , emitting an electron and antineutrino
  323. proton emission occurs when
    a proton inside a nucleus changes into a neutron . one of the up quarks has changed into a down quark . a positron and electron neutrino are emitted
  324. draw a diagram to show beta minus emission
  325. a transverse wave has oscillations at 
    right angles to its direction of travel 
  326. a longitudinal wave has oscillations that are
    parallel to its direction of travel 
  327. electromagnetic waves are emitted by the 
    oscillation of charged particles such as an electron . the oscillations sets up varying electric and magnetic fields that travel through space . the magnetic and electric fields are at right angles to each other and the direction of travel of the waves . the wave propagates through pace as a transverse wave without the need for any supporting medium  
  328. draw a diagram to show an electromagnetic wave 
  329. all waves electromagnetic waves travel at the same speed in a vacuum that is 
  330. the properties of the of the electromagnetic wave and the way that it interacts with matter depends on its 
  331. the distance between any two identical points on a wave is the
    • wavelength λ 
    • this is measured in metres 
    • for a pure sine wave it is the distance between any two adjacent crests or troughs 
  332. the time taken for a wave to go through a complete oscillation is the
    period , T 
  333. the number of oscillations per second is the 
    • frequency 
    • the frequency is measured in hertz 
  334. frequency = 
    • 1/period 
    • f = 1/T
  335. since speed = distance divided by time , the speed that a wave travels at , c , is given by 
    • c = λ/T or c = λ * 1/T
    • so c = fλ
  336. light is an 
    electromagnetic wave . visible light has a wavelength range from about 400nm (violet) to around 700nm (red)
  337. 1nm = 
  338. different wavelengths or frequencies of light gives us the impression of 
    different colours 
  339. larger amplitude waves increase the 
    intensity (brightness) of the light 
  340. like the rest of the electromagnetic spectrum , light can be 
    reflected , diffracted and refracted 
  341. the photoelectric effect was discovered towards the end of the 19th century . Experiments showed that 
    electrons could be emitted from the surface of a metal by illuminating the metal with light .
  342. however some of the experimental results seemed completely at odds with the wave theory of light 
    • the electrons are only emitted from the surface of the metal if the light is above a certain frequency 
    • the electrons are emitted with a range of kinetic energies from zero up to a maximum value
    • if the light is above the threshold frequency , then the number of electrons emitted per second is proportional to to the intensity of the light 
    • if light is above the threshold frequency , photoemission starts immediately the light falls on the surface no matter how low it intensity 
  343. if zinc is illuminated with visible light , no electrons are emitted . it is only when 
    uv light is used that there is any effect . every metal has its own particular light frequency known as the threshold frequency , below which there is no photoemission 
  344. the maximum kinetic energy is dependent on 
    the frequency of the light , not intensity . a faint uv glow would cause the emission of more energetic electrons than an intense red laser beam 
  345. electrons are held by 
    electrostatic forces onto the surface of the metal . the light has to provide enough energy to rip an electron free from the metal surface 
  346. the energy needed to remove an electron from the surface of a metal is called the 
    work function , denoted by Φ . this is usually given on electron volts and depends on the type of metal 
  347. the wave theory of light says that of a light wave hasn't got enough energy to release an electron then 
    you need a high amplitude wave i.e. a brighter light 
  348. but this doesn't work 
    • if the light wave is below the threshold frequency , it doesn't matter how intense it is there will be no photoemission 
  349. Einstein explained the photoelectric effect by using the idea of 
    photons . he realised that lift is absorbed in discrete packets or quanta of electromagnetic energy called photons . when a photon strikes a metal surface it is either totally absorbed or not at all . so when a photon strikes a metal surface and collides with an electron it will only dislodge an electron if its energy is greater than the work function 
  350. photoemission only occurs when 
    • E > φ 
    • or since E = hf where h is the planck constant , only when hf > φ 
  351. when photoemission just occurs the threshold frequency f0 is given by 
    f0 = φ/h 
  352. above the threshold frequency the photon 
    carries more than enough energy to release an electron . the excess energy goes into the kinetic energy of the emitted electron 
  353. Einstein's photoelectric equation expresses this in terms of the conservation of energy
    • energy of incident photon = energy needed to remove the electron (work function) + kinetic energy of the emitted electron 
    • hf = φ + EK 
    • Ek is the maximum kinetic energy of the electron ; if the electron has been emitted from deeper within the metal surface it may have a lower value of kinetic energy 
  354. in atomic and nuclear physics physicists use the electron volt as a convenient unit of energy . an electron volt (eV) is
    the amount of energy gained by an electron as it accelerates through a potential difference of 1 volt . 1 eV = 1.6 * 10-19

  355. a diffraction grating is a device which 
    splits light into different wavelengths , creating a spectrum 
  356. when an electric current is passed through a vapour of an element 
    the electrons collide with atoms of the vapour and light is given off . if the light is observed through a diffraction grating then each element is found to have its own set of bright emission lines . this is called line spectrum 
  357. for any specific element the spectral lines are always at the same
    frequency . to explain this we need to look again at our model of the atom 
  358. rutherfords model of the hydrogen atom has one electron orbiting a very , small , dense , positively charged nucleus . there is a problem with this model 
    • all charged particles emit radiation when they accelerate . the orbiting electron is accelerating to towards the centre of its orbit as it constantly changes direction . According to the laws of classical physics the electron should be radiating energy all the time . as it radiates it should lose energy , eventually spiralling down towards the nucleus .
    • this is rather like an artificial satellite that has dropped into a low orbit around earth . as the satellite passes through the upper atmosphere it loses energy and so it will inevitably drop further and spiral towards earth 
  359. Bohr suggested that the electron could
    travel in certain allowed orbits without losing energy . he called these allowed orbits stationary states . when the electron is an allowed orbit it doesn't radiate but stays at a constant energy 
  360. the energy levels are negative because 
    the electron is in a bound state - it is tied to the atom . The energy value of each allowed orbit tells you how much energy is needed to free the electron from the atom . By this convention higher energy levels are less negative ; an electron with zero energy is juts free of the atom 
  361. bohr proposed that an electron in an atom can only emit or absorb energy as 
    it moves from one allowed orbit to another . 
  362. this idea helped to explain the existence of line spectra 
    light is emitted from atoms when electrons lose energy, but in bohr's atom electrons can only lose energy in specified amounts as they jump down the energy levels . an electron can only move from one allowed state to another by gaining or losing exactly the right amount of energy . this is called electron transition . this  is why only certain frequencies of light appear in the line spectrum 
  363. each time an electron falls to a lower energy level it 
    • loses energy . this energy is radiated as a photon of frequency of f . so the energy of the emitted photon is 
    • E- E3 = ΔE = hf 
  364. when the electrons are in their lowest energy orbits , an atom is said to be in its 
    ground state 
  365. the lowest allowed orbit for a hydrogen atom has an energy of 
    -13.6 eV 
  366. when the hydrogen atom is the ground state its electron cannot 
    loose any more energy 
  367. the ground state is the preferred state for an atom but 
    electrons can move to higher energy levels if the atoms absorbs the correct amount of energy   this process could be caused by absorption of a photon of radiation of the right wavelength to by a collision with another electron 
  368. excitation is when 
    an atomic electron moves to a higher energy level 
  369. ionisation is when an 
    electron gains so much energy that its total energy becomes positive . this means that it becomes free of the atom 
  370. when an electric current is passed through a fluorescent lamp 
    • electrons collide with atoms or mercury vapour 
    • if an electron has sufficient energy greater thaN 6.7 eV , the collision will excite an electron in the mercury atom to a higher energy level 
    • as the atomic electron returns to its original state it emits a photon of uv light 
    • the photons of uv light are absorbed by atoms in the phosphor coating on the inside of the glass lamp , and electrons in these atoms are excited to higher energy states 
    • as these electrons fall to lower enemy states they emit photons of visible light 
    • the phosphors are carefully chosen to have the right energy levels to produce the required colour of light from the lamp 
  371. the wave theory successfully explains the way that 
    light is reflected and refracted and is important in interpreting the phenomena of diffraction and interference 
  372. however the wave theory cannot explain 
    • the photoelectric effect , nor black body radiation curves . these have been explained by thinking of light as as a stream of massless particles called photons which carry energy . this is an example of what is referred to as wave particle duality . 
    • there is no real contradiction here . the wave and particle theories compliment each other . the wave theory gives us an excellent way of picturing what happens as light passes from one place to another whilst the particle theory is useful in describing how light interacts with electrons  
  373. it isn't only light that shows aspects of wave and particle behaviour . electrons , which we have so far treated as point particles can be made to diffract . Louis de Broglie suggested in 1924 that all material particles should have a 
    • wave nature . he predicted that a particle of momentum p should have a wavelength given by wavelength = h/p or wavelength = h/mv 
    • where h is the planck constant . this is called the de broglie wavelength 

  374. this idea can be tested by trying to 
    diffract electrons through a suitable aperture 
  375. diffraction effects become noticeable when 
    the size of the aperture is of the same magnitude as the wavelength of the waves .
  376. an electron accelerated across a potential difference of 5kV will reach a velocity of around 4.2 * 107 ms-1 . this gives it a momentum of 3.3 * 10-23 kgms-1 . according to de Broglie's equation , the electron has wavelength of 
    • wavelength = h/p = 6.6 * 10-34/3.8 *10-23 = 1.7 * 10-11
    • this is about the size of gaps between layers of atoms 
  377. 4 years after de Broglie put forward his theory , George Thompson produced an electron diffraction pattern by 
    firing high speed electrons at gold foil . the emerging electron beam showed the same variation in intensity as light that has passed through a diffraction grating 
  378. today electron microscopes , which rely on the
    wave nature of electrons are in common use .there are also microscopes that use protons and even ions . since these particles are more massive and carry more momentum, their de Broglie wavelength is even smaller , which gives an improved resolution 
  379. the electron microscopes helps us to see much finer detail than is possible using a light microscope . this is because 
    it is diffraction that limits our ability to see fine detail . electrons diffract very little because they have a short wavelength 
  380. an electric current is defined as the 
    rate at which electrically charged particles pass through a point in the circuit 
  381. the size of the current is measured in 
    coulombs per second Cs-1 or amperes A 
  382. 1 Cs-1
    1 A 
  383. all current arrows on wires and component symbols point in 
    the conventional current direction i.e. the direction that a positive charge would move 
  384. in metallic conductors the charge carriers are 
  385. electrons move from 
    the negative supply of the dc terminal to the positive terminal . confusion can arise because current is usually shown as moving from the positive terminal to the negative terminal . this is referred to as conventional current 
  386. the size of the current is defined mathematically by
    • I = Q/T
    • where I = current in A 
    • Q = charge in C 
    • t = time in s 
  387. to make a current flow what must exist 
    a potential difference 
  388. potential difference is measured in 
    joules per coulomb or volts 
  389. the size of the potential difference is defined mathematically by 
    • V = W/Q 
    • where V = p.d. in volts 
    • W = work (energy) in joules
  390. a charge gains energy when it 
    passes through a cell 
  391. it releases the gained energy as it 
    passes through components in a circuit i.e. a pd exists across the component . thus both a cell and a component have a p.d. across them when charge flows in a circuit 
  392. charge fasses opposition when 
    they flow around a circuit , this is called resistance and its measured in ohms 
  393. the potential difference needed to make a current flow in a circuit depends on 
    the resistance in the circuit . the bigger the resistance , the more required to make a certain current flow 
  394. resistance is defined by the equation 
    R =V/I
  395. milli - 
    • 10-3
  396. micro 
    • 10-6
  397. kilo 
    • 103
  398. mega 
    • 106
  399. draw and explain a circuit used to produce current/voltage characteristics of components  

    • the component under test is placed between points x and y so that the circuit is complete when the switch is closed 
    • by varying the supply pd a range of current and pd values can be recorded for the component using the ammeter and voltmeter readings 
    • the battery is reversed and the supply pd varied over the same range to produce a second set of current and pd values 
    • a graph of the results can then be drawn , which is the characteristic curve for the component 
  400. draw a graph for current against pd for a resistor or wire (ohmic conductor) 
    the current and pd are directly proportional to each other . the conductor is said to follow ohms law 
  401. the diode is a 
    way device it acts like a valve 
  402. in the case of the semiconductor diode the shape of the curve obtained depends on the 
    direction in which the current is flowing 
  403. when the diode is forward biased (arrow facing the direction of conventional current) :
    • between 0 and about 0.7 volts , the diode offers a large resistance to current 
    • between about 0.7V and 1V the resistance of the diode falls rapidly and a large current flows - this is shown by the steep rise in the graph 
  404. draw a graph to show current against pd for a semiconductor diode 
  405. when the diode is reversed biased (arrow facing the opposite direction to conventional current) 
    • the diode offers high resistance , so very littler/no current flows 
    • at the breakdown voltage , typically between 50V and 500V , a large current flows 
    • most diodes cannot recover and are destroyed by the heating effect of the large current 
  406. filament lamp (non ohmic conductor) 
    • when the filament lamp is connected between X and Y and the voltage is steadily increased :
    • the graph becomes less steep 
    • the pd and current don't increase proportionally because the current heats the filament 
    • an increase of the temperature of the filament increases the resistance in the filament so decreases the rate of increase of current with pd 
    • the curve is symmetrical either side of the origin showing that the lamp behaves the same way for current flowing in either direction 
  407. draw a diagram to show how current varies with pd in a lamp 
  408. the same characteristics can be produced automatically using a 
    voltage sensor (V) and current sensor (A) . these together with a data logger (D) capture data which is then fed into the computer for analysis 
  409. draw a typical set up
  410. ohms law states that 
    the current in a conductor is directly proportional to the p.d. across it provided that the temperature and other physical conditions remain the same