Physics A2 Level

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Physics A2 Level
2011-12-15 04:48:21
physics alevel key words

Key Words Unit 4
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  1. Force
    rate of change of momentum
  2. Momentum
    mass times velocity
  3. Newton's laws of motion
    • First law: an object continues at rest or in uniform motion unless it is acted on by a resultant force
    • Second law: the rate of change of momentum of an object is proportional to the resultant force on it
    • Third law: when two objects interact, they exert equal and opposite forces on one another
  4. Newton's law of gravitation
    the gravitational force F between two point masses m1 and m2 at distance r apart is given by F=Gm1m2/r2
  5. Impulse
    force times time for which the force acts on an object
  6. Principle of conservation of momentum
    when two or more bodies interact, the total momentum is unchanged, provided no external forces act on the bodies
  7. Conservation of momentum
    for a system of interacting objects is the total momentum of the objects remains constant provided no external resultant force acts on the system
  8. Kinetic energy
    the energy of a moving object due to its motion
  9. Explosion
    when two objects fly apart, the two objects carry away equal and opposite momentum
  10. Elastic collision
    a collision in which the total kinetic energy after the collision is equal to the kinetic energy before the collision
  11. Uniform circular motion
    motion of an object moving at a constant speed along a circular path
  12. Angular displacement
    the angle an object in circular motion turns through
  13. Angular speed
    the rate of change of angular displacement of an object in circular motion
  14. Centripetal acceleration
    for an object moving at speed v in uniform circular motion its centripetal acceleration a=v2/r towards the centre of the circle
  15. Centripetal force
    the resultant force of an object that moves along a circular path
  16. Equilibrium
    state of an object when at rest or in uniform motion
  17. Amplitude
    the maximum displacement from equilibrium of an oscillating object
  18. Displacement
    distance in a given direction
  19. Free oscillations
    oscillations where there is no damping and no periodic force acting on the system so the amplitude of the oscillation is constant
  20. Time period
    time taken for one complete cycle of oscillations
  21. Frequency
    the number of cycles of oscillation per second
  22. Angular frequency
    for an object oscillating at frequency f in simple harmonic motion its angular frequency = 2pif
  23. Phase difference
  24. Simple harmonic motion
    motion of an object if its acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position
  25. Dissipative forces
    forces that transfer energy which is wasted
  26. Damped oscillations
    • oscillations that reduce in amplitude due to the presence of resistive forces such as friction and drag
    • 1.Lightly damped system: amplitude of oscillations decreases gradually
    • 2.Heavily damped system: the system slowly returns to equilibrium without oscillating
    • 3.Critically damped system: system returns to equillibrium in the least possible time without oscillating
  27. Periodic force
    a force that varies regulary in magnitude with a definite time period
  28. Natural frequency
    the frequency of free oscillations of an oscillating system
  29. Forced oscillations
    oscillations of a system that is subjected to an external periodic force
  30. Resonance
    the amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the resonance frequency of the system
  31. Resonant frequency
    the frequency of an oscillating system in resonance
  32. Gravitational field
    the region surrounding an object in which it exerts a gravitational force on any other object
  33. Line of force/ Field line
    a line followed by a, small mass in a gravitational field/ a small positively charged object in an electric field/ a free north pole in a magnetic field, acted on by no other forces than the force due to the field
  34. Radial field
    a field in which th field lines are straight and converge or diverge as if from a single point
  35. Uniform field
    a region where the field strength is the same in magnitude and direction at every point in the field
  36. Gravitational potential
    the work done per unit mass to move a small object from infinity to that point in a gravitational field
  37. Gravitional potential energy
    the work done to move a small object from infinity to that point in the field
  38. Potential gradient
    • at a point in a field is the change of potential per unit charge of distance along the field line at that point
    • -the field strength at any point
  39. Gravitational field strength
    the force per unit mass on a small mass placed in the field
  40. Gravitational force
    an attractive force that acts equally on any two objects due to their mass
  41. Kepler's third law
    for any planet, the cube of its mean radius of orbit is directly proportional to the square of its time period
  42. Universal constant of gravitation/ Gravitational constant
    the constant of proportionality in Newton's law of gravitation
  43. Electrical conductors
    an object that can conduct electricity
  44. Free electrons
    electrons in a conductor that move about freely inside the metal because they are not attached to a particullar atom
  45. Gold leaf electroscope
    a device used to detect electric charge
  46. Insulating materials
    a material that cannot conduct electricity
  47. Electric field strength
    the force per unit charge on a small positively charged object at a point in an electric field
  48. Electric potential
    the work done per unit charge on a small positively charge object in an electric field to ove it from infinity to that point in the field
  49. Equipotentials
    a line or surface in a field along which the electric or gravitational potential is constant
  50. Coulomb's law
    • for two point charges Q1 and Q2 at distance apart r, the force between the two charges
  51. Capacitance
    • the charge stored per unit pd of a capacitor
    • unit- farad (F)= 1 coulomb per volt
  52. Time constant
    the time taken for a quantity that decreases exponentially to decrease to 0.37 (=1/e) of its initial value
  53. Capacitor energy
    energy stored by the capacitor
  54. Capacitor discharge
    through a fxed resistor of resistance R, time constant= FC
  55. Motor effect
    the force on a current-carrying conductor due to a magnetic field
  56. Fleming's left-hand rule
    rule that relates the directions of the force, magnetic field and current on a current-carrying conductor in a magnetic field
  57. Magnetic flux density
    the magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines
  58. Simple electric motor
    an electric motor with an armature consisting of a single coil of insulated wire
  59. Hall probes
    a device used to measure magnetic flux density
  60. Magnetic force
  61. Electromagnetic induction/ Induced emf
    the generation of an emf when magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines
  62. Fleming's right-hand rule/ Dynamo rule
    rule that relates the directions of the induced current, magnetic field and velocity of the conductor when the conductor cuts across magnetic field lines and an emf is induced in it
  63. Lenz's law
    when a current is induced by electromagnetic induction, the direction of the induced current is always such as to oppose the change that causes the current
  64. Magnetic flux
    equals BA for a uniform magnetic field of flux density B that is perpendicular to an area A
  65. Magnetic flux linkage
    through a coil of N turns, = NBA
  66. Faraday's law of electromagnetic induction
    the induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit
  67. Transformer
    • converts the amplitude of an alternating pd to a different value
    • it consists of two insulated coils, the primary and secondary coil, wound round a soft iron laminated core
  68. Step-up transformer
    a transformer in which the rms pd across the secondary coil is less than the rms pd applied to the primary coil
  69. Step-down transformer
    a transformer in which the rms pd across the secondary coil is greater than the rms pd applied to the primary coil
  70. Transformer rule
    the ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of secondary turns to the number of primary turns
  71. Transformer Efficiency
    for an ideal transformer the output power equals the input power
  72. Eddy currents
    unwanted induced currents in the metal parts of ac machines
  73. National Grid System
    the network of transformers and cables that is used to distribute electrical power from power stations to users
  74. Back emf
    • emf induced in the spinning coil of an electric motor or in any coil which the current is changing
    • acts against applied p.d.