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PH5 definitions

nicola.bowen Englisch 49 Karten

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  1. 1CapacitorA pair of conducting plates separated by an insulator. If a p.d. is placed across the plates they acquire equal and opposite charges.
  2. 2Capacitance, C, of a capacitor(Charge on either plate)/(p.d. between plates) units F(farad)
  3. 3DielectricInsulator between plates of a capacitor, also serving to make the capacitance larger than if there were just empty space
  4. 4Magnetic field strength BA vector quantity.. Direction is that in which the North pole of a freely pivoted magnet points. Magnitude defined by F=BIL where F is the force on a length L of wire carrying a current I placed perpendicular to the direction of the field. Units T(tesla)
  5. 5Hall voltageWhen a magnetic field B is applied to a conductor carrying a current I at right angles to the field direction a so called hall voltage appears across the specimen at right angles to the B and I directions
  6. 6AmpereThe ampere is that current which, when flowing through two infinite parallel wires, one metre apart in vacuum, produces a force between the wires of exactly 2x10^(-7) N per methre of length. Units A
  7. 7Magnetic fluxIf a single turn coil of wire encloses an area A and a magnetic field B makes an angle o with the normal to the plane of the coil, the magnetic flux through the coil is given by ABcos(o). Unit Wb(weber)
  8. 8Flux linkageIf the above coil consists of N turns the flux linkage is given by N*magnetic flux. Unit Wb or Wbturn
  9. 9Faraday's LawWhen the flux linking an electrical circuit is changing an emf is induced in the circuit of magnitude equal to the rate of change of flux linkage.
  10. 10Lenz's LawThe direction of any current resulting from an induced emf is such as to oppose the change in flux linkage that is causing the current.
  11. 11Root mean square (RMS) valueIf an alternating voltage is read at regular intervals throughout a cycle, giving the values V1,V2..VN the rms p.d. is defined as Vrms =root(1/n V1^2 + V2^2....+Vn^2)
  12. 12Alpha radiationFast moving particles, helium nuclei, ejected from certain radioactive nuclei
  13. 13Beta radiationElectrons with speeds just less than the speed of light, ejected from certain radioactive nuclei
  14. 14Gamma radiationPhotons of high energy (high frequency, short wavelength) ejected from radioactive nuclei
  15. 15A/Z X notationX is the chemical symbol of the element, A is the mass number and Z the atomic number
  16. 16Half life of a nuclideThe time taken for the number of radioactive nuclei N to reduce to one half of the initial value. Unit s
  17. 17Activity AThe rate of decay (number of disintegrations per second) of a sample of radioactive nuclei. Unit Becquerel (Bq)
  18. 18Decay constantThe constant which appears in the exponential decay law N=Noe^(-lamdat) and determines the rate of decay (the greater lamda the more rapid the rate of decay) lamda is related to half-life by (ln2)/half life =lamda. Units /s
  19. 19Radio-isotopesIsotopes of an element have the same atomic number Z but a different mass number A; radio isotopes are simply isotopes which are radioactive.
  20. 20Unified atomic mass unit uThe unified atomic mass unit is defined as exactly 1/12 of the mass of one atom of carbon -12. Thus one atom of carbon 12 has a mass of exactly 12u
  21. 21Electron-voltThis is the energy transferred when an electron moves between two points with a potential difference of 1 volt between them. 1eV = 1.6*10^(-19)J. So for an electron being accelerated it is the KE acquired when accelerated though a p.d of 1V
  22. 22Binding energy of a nucleusThe energy that has to be supplied in order to dissociate a nucleus into its constituent nucleons. (Not energy the nucleus possesses) unit J
  23. 23Conservation of mass-energyEnergy cannot be created or destroyed, only transferred from one form to another. We can measure the energy in a body by multiplying its mass by c^2
  24. 24Nuclear FissionCertain nuclei of large mass number can absorb a neutron and will then split into two smaller, beta radioactive, nuclei. Two or more neutrons are also released. The fragments have larger kinetic energies. This is called nuclear fission.
  25. 25Chain reactionA chain reaction is repeated events of nuclear fission in a sample of fissile material, initiated by neutrons released in previous fissions
  26. 26X-raysHigh energy e-m radiation with photon energies between 100eV and 100keV
  27. 27A-scanScan in which the strength of reflections of an ultrasound pulse from interfaces in the body is shown by the amplitude of a trace.
  28. 28B-scanScan in which the strength of reflection of an ultrasound pulse from interfaces in the body is shown by the brightness of a trace. An array of transducers can produce a 2D image.
  29. 29Acoustic impedanceThe property of materials which determines the fraction reflected.
  30. 30Coupling mediumGel or oil used to exclude air between the skin and the ultrasound transducer. It reduces the mismatch in Z and enables more ultrasound to enter the body instead of being reflected off the skin.
  31. 31PrecessionThe spin direction of protons rotate around the magnetic field direction, like a child's top.
  32. 32Relaxation timeThe time taken for the protons to flip back to their lower energy state.
  33. 33ECGProduced due to the nervous impulses associated with the heart beat being detected outside the body, a voltage time chart.
  34. 34Atrium/atriaThe top chambers of the heart
  35. 35VentricleThe lower chambers of the heart
  36. 36Sino-atrial nodeSends a signal which triggers the muscles of the heart to contract. Located at the top right of the heart.
  37. 37Surface potentialVoltage measured on the skin due to nerve signal within the body.
  38. 38ContractionShortening of muscles in response to nerve stimulus.
  39. 39Absorbed doseThe radiation energy absorbed per kilogram of tissue.
  40. 40Dose equivalentQ * absorbed dose in which Q is a factor which depends on the type of radiation and takes account of the biological effect of the radiation.
  41. 41Quality factor (Q)20 for alpha radiation and 1 for beta and gamma in equation: dose equivalent = Q *absorbed dose
  42. 42Radioactive tracerChemical compounds with an atom replaced by a radioactive isotope - used to track the uptake of the compound by the body.
  43. 43TracerUsed to investigate function of particular organs
  44. 44Electron captureA method of decay where an element reacts with an electron to produce an isotope in an excited state which gives off gamma radiation.
  45. 45CollimatorDevice for producing a parallel beam
  46. 46Scintillation crystalFlashes of light are given out by certain crystals when high energy particles strike them.
  47. 47PhotomultiplierAn arrangement of electrodes with different voltages applied to them, so that electrons emitted from one electrode by the photoelectric effect are effectively multiplied in number to make a much larger current.
  48. 48PositronThe antiparticle of an electron, the particle emitted in B+ decay.
  49. 49AnnihilationWhen a particle and its antiparticle meet at low speed their mass energies are converted into photons

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Karteikarten am PH5 definitions, erstellt von nicola.bowen am 23/03/2014.
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