A-Level物理definition.doc

qq:309043482email:teacher: CJConcepts1. scalar quantityA quantity which gives its magnitude2.vector quantity A vector quantity has magnitude and direction3.systematic uncertaintyresult in all readings being either above or below the accepted value.4. random uncertaintyresult in readings being scattered around the accepted value5. accuracythe degree to which a measurement approaches the true value.6. precisionpart of accuracy which is within the control of the experimenter6.displacementthe distance move in a specific direction7.velocitythe rate of change in displacement8.accelerationthe rate at which the velocity of the particle is changing.9.Newtons first law of motionAn object at rest will stay at rest and an object in motion will stay in motion with the same speed and in the same direction if there is no resultant force act on it10. inertia惯性the resistance an object has to a change in its state of motion.11. Newtons second law of motionFor a body of constant mass, its acceleration is directly proportional to the net force applie to it.12. One Newtonthe force which will give a mass of one kilogram an acceleration of one meter per second square in the direction of the force13.Newtons third Law of Motion(1)Whenever one body exerts a force on another, the second exerts an equal and opposite force on the first.(2) To every action, there is an equal and opposite reaction.14. Massa measure of a bodys resistance to changes in motion15. There are something different between mass and weight(i) Mass is a scalar; a measure of a bodys resistance to changes in motion; it is constant and the property of the body.(ii) Weight is a vector; it is equal to the product of mass and gravitational acceleration; it will change with the altitude changed.16.The linear momentum of an objectthe product of mass and its velocity.17. impulsethe product of the force acting on a body and the time interval over which the force acts18. The principle of conservation of linear momentumthe total momentum of a closed system of colliding objects remain constant if no external forces act on that system. Force=rate of charge of momentum19. pressureForce per unit area20. upthrustequal to the weight of the liquid displaced by that object.21. frictional forceThey are produced when two surface move or try to move in opposition to each other.22. centre of massa single point at which the whole mass of the body of system is assumed to be concentrated23. centre of gravitya single point at which the whole weight of the body acts.24. moment/ torque of a forcethe product of that force and the perpendicular distance from the line of the action of the force to the point.25. coupleA couple consists of two forces, equal in magnitude but opposite in direction whose lines of action do not coincide26. moment of a couplethe product of one of the forces and the perpendicular distance between the two forces.27. There are two conditions for the equilibrium of forces acting on a rigid body(1)The vector sum of all the forces acting on a rigid body must be zero.(2) The vector sum of all external torques acting on a rigid body must be zero.28. the principle of momentwhen a body is in equilibrium, the sum of the clockwise moment about a point must be equal to the sum of the anticlockwise moments about that point 29. energyEnergy is the ability to do work.30. The principle of conservation of energyThe total energy in a given system is always constant. It can be transformed from one form to another but cannot be created or destroyed31.work donethe product of the magnitude of the force and the displacement of the particle in the direction of the force.32. kinetic energythe ability to do work due to the motion33.potential energythe ability of to do work as a result of its position or shapeGravitational potential energy - the ability to do work due to the position changed in the gravitational field.Electric potential energy - the ability to do work due to the position changed in the electric field.Elastic potential energy - the energy due to the shape changed.34. internal energyThe total kinetic and potential energy associated with the motions and relative positions of the molecules of an object.Kinetic energy is depended on the absolute temperature T.Potential energy is depended on the separation of the molecules.35.powerthe rate of doing work36.densitymass per unit volume37. the spacing of solid, liquid and gasthe average spacing of atoms in liquid is up to about twice that in solid, or still of the order of 10-10 m. for gas, the average spacing if of the order of 10-9m38. Brownian MotionRandom movement of particles39. The conditions to increase the speed of Brownian motion(1)the temperature of the fluid was raised, (2)the viscosity of the fluid was lowered,(3)the size of the particles was reduced.40. Crystalline solidsParticles in a regular arrangement, (lattice) repeats itself41. polymerLong chain molecules, some cross-liking between chains42. amorphous disordered arrangement of particles, any ordering is short-range.43. Pressureforce per unit area, where the force F acts perpendicular to the area A. 44. Heata form of energy that is transferred from one region to another as a result of a temperature difference.45. Meltinga substance changes its state from solid to liquid at a definite temperature.46. Boilinga liquid changes into vapor at a definite temperature.47. EvaporationMolecules are lost from the surface of a liquid at any temperature48. The distinguish between evaporation and boilingSame:The both represent a change of state from liquid to vapor.Difference:(1)Evaporation takes place at any temperature, but boiling only happens at a fixed temperature for a given pressure of the surroundings.(2)Evaporation takes place at the surface of the liquid, whereas boiling occurs in the body of the liquid.49. deformationThe change of shape50. Hookes lawprovided the elastic limit is not exceeded, the extension of a body is proportional to the applied load. 51. strainthe ratio of extension and the original length.52.stressthe ratio of the force and the area53. elastic deformation and plastic deformationElastic deformation: the material returns to its original shape when the external forces are removed.Plastic deformation: the material does not return to its original shape when the external force are removed. 54. Strain energy/ elastic potential energyThe energy stored in a body due to change of shape. It is the ability to do work55. ultimate tensile stressIt equals to the maximum force divided by the original cross-section area of the wire56. progressive waves.Transfer of energy as a result of vibrations57. the displacement of the particlea waves distance from its rest position58. amplitudethe maximum displacement of a particle in the wave.59.wavelengththe distance moved by the wave during one oscillation of the source of the waves.60. periodThe period of the wave is the time for a particle in the wave to complete one vibration, or one cycle61. frequencyThe number of complete vibrations (cycles) per unit time of a point on the wave62. intensityThe amount of energy passing through unit area per unit time63. transverse wavethe vibrations of the particles in the wave are perpendicular to the direction in which the energy of the wave is travelling.64. longitudinal wavethe direction of the vibrations of the particles in the wave is along the direction in which the energy of the wave is travelling.65. polarisationVibration in one direction66. electromagnetic waves(1)All electromagnetic waves are transverse waves.(2)Electromagnetic waves show all the properties common to wave motions(3)In a vacuum all electromagnetic waves travel at the same speed67. The principle of superpositionwhen two or more waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves at that point.68. stationary waveIt is formed by interference of two waves of same frequency travelling in opposite direction69.node and antinodeNode: at the ends of the string there is no vibration.Antinode: at the centre of the string; a point of maximum amplitude 70. diffractionWhen a wave passes through a slit, the wave spreads out71. interferencethe superposition of two or more wave trains from coherent source.72. the conditions for coherent(1) waves are in phase or move with a constant phase difference(2) waves have the same frequency and wavelength.73. the conditions for interference(1) the sources must have the same or roughly equivalent amplitude.(2) the sources must be coherent.(3) transverse waves must not be polarized.74. the conditions can increase the brightness of the pattern(1) decrease the wavelength of the incident wave.(2) decrease the distance between the slits and the screen.(3) increase the width of the slits(4) increase the amplitude of the incident wave.75. the conditions of increasing the width of the fringe(1) increase the wavelength of the incident wave(2) increase the distance between the slits and the screen(3) decrease the distance between the two slits76. electric fieldRegion where a charge experience a force77. electric field strength at a pointForce per unit positive charge78. For any electric field:1. the lines of force start on a positive charge, and end on a negative charge2. the lines of force are smooth curves which never touch or cross3. the strength of the electric field is indicated by the closeness of the lines. The closer they are, the stronger the field.79. potential difference between two pointsequal to the work done by an external force in moving a unit positive charge from a point at lower potential to a point at higher potential 80. currentthe rate of flow of electric charges Q through a given cross-section of a wire.81. one coulombThe coulomb is that charge passing a point in a circuit when there is a current of one ampere for one second82. one voltOne joule per coulomb83. resistancethe ratio of the potential difference across the wire to the current84. Ohms lawthe current flowing in a metallic conductor is proportional to the potential difference across it , provided physical conditions are constant.85. e.m.f The e.m.f of a source is the potential difference across its terminals when no current is drawn from the source.86. distinguish between e.m.f. and p.d87. Kirchhoffs first lawThe sum of currents entering a junction equal to the sum of currents leaving that junction.(the conservation of charge)88. Kirchhoffs second lawThe sum of the e.m.f. is equal to the sum of the potential drops round any closed circuit loop.(conservation of energy)89. In -particle scattering experimentwe know the two facts(1) most -particle