AQA AS Physics unit two

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AQA AS Physics unit two
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  1. Absolute refractive index
    Property of the optical material equal the ratio : speed of light in a vacuum/speed of light in the material
  2. Acceleration
    The rate of change of velocity : change in velocity/time taken ; unit m s-2
  3. Acceleration due to gravity
    The rate at which all objects Accelerate under gravity if air resistance is neglected ; also known as the acceleration of free fall ; on earth its usually taken as 9.81 m s-2 , but it varies slightly from place to place
  4. Amplitude
    The maximum height of a wave , or the largest displacement from equilibrium
  5. Anti node
    A point on a standing wave where the amplitude is at a maximum
  6. Anti phase
    Two points on a wave , or points on two waves , are in anti phase if their vibrations are 180° out of phase with each other
  7. Breaking stress or ultimate tensile stress
    The maximum stress (force per unit area) that a material can withstand before it breaks
  8. Brittle
    A brittle material fractures before it undergoes plastic deformation
  9. Centre of gravity
    The point at which the weight of an object can be taken to act ; an object will balance if its supported at its centre of gravity
  10. Centre of mass
    The point at which the mass of an object can be taken to be concentrated ; in a uniform gravitational field this is the same as the centre of gravity
  11. Cladding
    A layer of glass (or plastic) that surrounds the central core of an optical fibre
  12. Coherent
    Two or more waves that have a fixed phase difference are said to be coherent
  13. Component
    A vector can be split up into perpendicular components ; the vertical component is the part of the vector that acts in a vertical direction
  14. Compression
    An object in compression is under the influence of forces that tend to squash it
  15. Coplanar forces
    A two dimensional system of forces that all act in the same plane ; they can be drawn on a piece of paper
  16. Couple
    Two equal forces that act in opposite directions on an object so as to cause rotation
  17. Critical angle
    The minimum angle of incidence at an optical boundary at which total internal reflection occurs
  18. Density
    The amount of mass per unit volume
  19. Diffraction
    The spreading of waves through an aperture or round an obstacle
  20. Diffraction grating
    A series of closely spaced parallel slits through which light can diffract ; used to create spectra
  21. displacement
    a vector describing the difference in position of two points
  22. Drag
    Resistive force , such as air resistance , which acts to oppose motion in a fluid
  23. Ductility
    The ability of materials to show extended plastic deformation and become elongated under tension ; a ductile metal can be drawn out into wires
  24. Efficiency
    The ratio : useful energy transferred (or work done) / total energy input ; this is always less tHan 10
  25. elastic behavIour (elasticity)
    When a material returns to its original dimensions after deforming force is removed
  26. Elastic strain energy
    The potential energY stored in an elastic material that has been extended
  27. Endoscope
    A medical device that used optical fibres to see inside the body
  28. energy
    The ability to do work I.e. Move a force through a distance ; a scalar quantity , measured in joules
  29. Equilibrium
    An object is said to be in equilibrium if its not accelearting
  30. First order maximum
    A point  at which the waves passing through a diffraction grating interfere constructively ; waves from adjacent slits have a path difference one wavelength , and so all to wave arrive in phase
  31. Free body diagram
    A simplIfied picture of a physical situation which shows all of the relevant forces acting on a body
  32. Frequency
    The number of waves passing a point in one second , measured in hertz , Hz
  33. Friction
    A force that acts between surfaces , acting so as to oppose their relative motion
  34. Fundamental frequency
    The lowest resonant frequency of a vibrating system or a standing wave
  35. Gravitational potential energy
    The energy stored by a mass due to its position in a gravitational field ; in a uniform field ,the gravitational potential energy of a mass , m , that is raised by a distance , delta h , is given by Ep = mg delta h
  36. hookes law
    Law stating that , for an object under tension , such as a wire or a spring , the extension is proportionAl to the applied force
  37. Inertia
    An objects resistance to acceleration ; for linear motion , this is the mass
  38. instantaneous velocity
    The rate of change of displacement , as measured over a very small time interval
  39. Interference partern
    A Series of maxima (points of constructive interference) and minima (Points of destructive interference) in a region where two or more waves overlap
  40. Kinetic energy
    The energy of a mass , m , moving at a velocity  Ek = 1/2mv2
  41. Laser
    A device that produces a highly monochromatic , coherent , non diverging light beam
  42. Longitudinal wave
    A wave that has oscillations parallel to the direction of travel of the wave
  43. Newton
    the S.I. unit of force ; 1 newton is the force that will Accelerate the mass of 1 kg at 1ms-2
  44. Node
    A poInt on a standing wave at which the amplitide is zero
  45. optical fibre
    A think strand of glass or plastic which carries light signals
  46. Overtone
    A vibration with a frequency that is a multiple of the fundamental frequency
  47. Parallelogram law
    A method for finding the resultant force of two vectors
  48. path difference
    The difference in the distance travelled by two waves ; commonly expressed as the number of wavelengths
  49. phase difference
    The difference in phase (the position in the cycle) of two waves , expressed in degrees or radians
  50. In phase
    Two waves are in phase if they are at the sAme point in their cycle at the same time
  51. plastic behaviour
    When a material if permanently deformed , even after the applied force is removed
  52. Polarised
    A transverse wave that is constrained to vibrate in one direction only is said to be polarised
  53. Power
    The rate at which energy is transferred or the rate at which work is done , measured in joules per second , or watts , W ,
  54. principle of conservation of energy
    law stating that the total energy of a closed system is constant
  55. principle of moments
    law stating that if an object is in equilibrium , the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about that point
  56. principle of superposition
    law stating that when two similar waves overlap , the total disturbance caused is the vector sum of the individual disturbances
  57. progressive wave
    a wave that transfer energy in the direction of the wave travel
  58. rarefaction
    a region of lower pressure or density in a longitudinal wave
  59. refraction
    the change in direction of a wave as it crosses a boundary between two mediums in which its speed differs
  60. refractive index (absolute refractive index) (n)
    property of an optical material equal to the ratio : speed opt light in a vacuum / speed of light in the material
  61. relative refractive index n2
    the relative refractive index of material 2 relative to material 1 (n2) is the ratio of : speed of light in medium 1 / speed of light in medium 2
  62. resolution or resolving
    the splitting up of a vector into components , usually perpendicular
  63. resultant
    the sum of two or more vectors such as forces
  64. scalar
    a physical quantity that is fully specified by its magnitude (size) ; it has no direction associated with it
  65. snells law
    law of refraction connecting the angle of incidence and angle of refraction with the absolute refractive indices of the materials either side of the boundary : n1sinθ1 : n2sinθ2
  66. spectrometer
    a device that uses a diffraction grating to produce spectra or to measure the wavelength of monochromatic light
  67. spectrum
    the distribution of wavelengths in a light source
  68. spring constant k
    the force needed to stretch a spring by unit extension k = force/extension unit Nm-1 its usually a measure of the stiffness of a spring
  69. stationary or standing wave
    a wave that doesn't transfer energy in the direction of wave travel ; it has stationary points called nodes
  70. stiffens
    the resistance to extension of a material under tension
  71. strain or tensile strain ε
    • the fractional increase in length of a wire , l , under tension 
    • ε = Δl/l
    • it has no unit
  72. strength
    a measure of the force (stress) needed to cause fracture of a material
  73. stress or tensile stress σ
    • the force per unit cross sectional area 
    • σ = F/A
  74. tensile force
    a force acting to cause extension
  75. tension
    an object in tension is under the influence of of forces which tend to extend it
  76. terminal velocity
    the steady velocity reached by a falling object when the drag is equal to the weight
  77. torque
    • the rotational equivalent of a force
    • torque produces rotational acceleration 
    • unit Nm
  78. [total internal reflection
    the complete reflection of a light ray at the boundary of two media , when the ray is in the medium with a lower speed of light
  79. transverse wave
    a wave that has oscillations perpendicular to the direction of wave travel
  80. ultimate tensile stress or breaking stress
    the maximum stress (force per unit area) that a material can withstand before it breaks
  81. upthrust
    the upward force on an object that is submerged in a fluid ; it is equal to the weight of the fluid displaced
  82. vector
    a physical quantity that is specified by its magnitude and direction
  83. velocity
    the rate of change of displacement ; velocity = change in displacement/time ; unit ms-1
  84. watt
    unit of power equal to the rat elf energy transfer of 1 joule per second
  85. wavelength
    the distance between consecutive points on a wave that have identical motion
  86. work
    work done = force x distance moved in the direction of the force
  87. yield point
    the minimum stress at which plastic deformation occurs
  88. young modulus
    the stiffness constant of a material , defined by the ratio : tensile stress/tensile strain
  89. zero orde maximum
    the central point at which the wave passing through a diffraction grating interfere constructively ; waves from adjacent slits have zero path difference and so all waves arrive in phase
  90. physical quantities can be classified into two groups
    scalars or vectors
  91. give an example of a scalar quantity
    • temperature
    • mass
  92. scalar quantities must have
    a magnitude but no direction associated with them
  93. give an example of a vector quantity
    • velocity 
    • force
  94. a vector quantity is only fully specified when
    the magnitude and direction is given
  95. draw a table to show examples of scalar and vector quantities met in this unit
    x
  96. a vector quantity has
    magnitude and direction whereas a scalar quantity only has magnitude
  97. vector quantities are often identified by the use of
    bold type
  98. when two vectors are added
    we need to take account their direction as well as their magnitude
  99. two vectors can be added by
    drawing a scale diagram showing the effect of one vector followed by the other
  100. the sum of a number of vectors is known as the
    resultant
  101. the resultant is
    the single vector that has the same effect as the combination of the other vectors
  102. it is vital to take into account the relative direction of vectors when
    adding them together , for example the resultant of two 5N forces could be anything from 0 to 10N  depending on their directions
  103. the resultant of two vectors can be also be found by the
    parallelogram law . a parallelogram is constructed using the two vectors as adjacent sides . the resultant is the diagonal of the parallelogram
  104. if the vector diagram is drawn to scale , the resultant vector can be found by
    direct measurement from the diagram
  105. for two vectors at right angles , the magnitude of the resultant can be found from
    calculation by using pythag
  106. subtracting a vector quantity can be though of as
    adding a negative vector . the vector which is to  be subtracted is reversed in direction . this reversed , or negative , vector is then to be added in the usual way
  107. a single vector can be replaced by a combination of two of more vectors that would have the same effect this is known as
    resolving a vector into its components and can be found as the reverse of finding the resultant . the components of a vector could be at any angle but it is often useful to use two components that are at right angles to each other . this might be to find the horizontal and vertical components of a force or a velocity
  108. remember that the vector you are resolving is always the
    hypotenuse of a triangle . the components will always be smaller than the original vector
  109. it is often important to be able to identify and add together all the forces that are acting on an object . the size and direction of the resultant will
    determine what happens to the object
  110. everyday objects are subjected to a variety of forces such as
    • weight 
    • contact forces 
    • friction
    • tension 
    • air resistance 
    • buoyancy
  111. all of those forces are
    electromagnetic in origin except for weight . they arise because of the attraction or repulsion of the charges in atoms
  112. the weight is the
    force that acts on mass due to the gravitational attraction the earth
  113. the gravitational field strength on the earth is
    • 9.81 Nkg-1 
    • this means that every kilogram of mass is attracted towards the earth with an attraction of 9.81 N
  114. the weight of an object in newtons is given by
    • weight (N) = mass (kg) 8 gravitational field strength (Nkg-1)
    • w=mg
  115. the goal weight of a real object is
    the sum of the gravitational attractions acting on every particle in the object . the resultant of these forces is the weight of the object which can be treated as a single force acting at one point in the object , this is known as the centre of gravity
  116. whenever two solid surfaces touch they
    exert a contact force on each other . this force is known as the reaction . it is the contact force between the floor and your feet that stops gravity pulling your feet through the ground . the resultant contact force between two surfaces could be at any angle
  117. we usually split the contact force into two components
    • the normal contact force acting perpendicularly to the two surfaces
    • the frictional force acting parallel to the surfaces
  118. a frictional force acts
    between two surfaces whenever there is a relative motion between them , or when an external force is trying to slide past each other
  119. an object is said to be in tension when
    a force is acting to stretch the object . elastic materials , like ropes or metal cables resist this stretching and exert a force on the bodies trying to stretch them
  120. ay object that is moving through a fluid is subject to
    a resistive force or drag . any object moving through the atmosphere has to push the air out of the way , this gives rise to the drag force that acts to oppose relative motion between the object and the fluid
  121. the size of the air resistance acting on an object depends on
    the area of the object and the density of the air . the air resistance also increases as the relative speed between the object and the air increases . so as you go faster the force trying to stop you increases
  122. buoyancy - any objects that are partly or fully submerged in a fluid like a boat floating on water or a hot air balloon floating in the atmosphere are subject to
    an upthrust from the surrounding fluid
  123. free body diagrams - the forces acting on a real object may be ver complex . a free body diagram is an attempt to
    model the situation so that we can analyse the effect of the forces . the free body diagram is used to show all external forces that are acting on an object . since forces are vector quantities they are represented by arrows , drawn to scale and acting in the correct direction 

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