Chapters 7 to 9

• Wave


  A disturbance that transfers energy from place to place
• Medium


  The material through which a wave travels
• States of matter that can be a medium

  • Gas
  • Liquid
  • Solid
  • Any other states of matter
• A wave does NOT carry matter with it! It just moves the matter as it goes through it
• Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points
• Vibration


  A repeated back and forth or up and down motion
• Not all waves require a medium to travel. Light from the sun travels through empty space
• Types of waves


  • Mechanical wave
  • Non-mechanical wave
• Mechanical wave


  A periodic disturbance in a medium that carries energy from one point to another
• Non-mechanical wave


  Defined in a vacuum of space, unified existing laws of electricity and magnetism, oscillating electric field produces a magnetic field (and vice versa) - propagates an electromagnetic wave
• Electromagnetic wave


  Electric field (E) perpendicular to magnetic field (M), travels at velocity c (3.0 x 10^8 ms^-1 in a vacuum)
• Types of waves based on motion

  • Transverse wave
  • Compressional wave
• Transverse wave


  Waves that move the medium at right angles to the direction in which the waves are traveling
• Compressional wave


  Matter vibrates in the same direction as the wave travels
• Positive and Negative Charge


  Electrons are stripped from one component and transferred to the other to cause both to be oppositely charged
• Atoms


  Composed of protons (+), electrons (-) and neutrons
• Nucleus


  Contains the protons and neutrons
• Electrons


  Surround the nucleus
• Protons


  Much larger than electrons in mass but have an equal and opposite charge
• Coulomb (C)


  Unit of electric charge
• Basic quantity of electric charge (e)

  1.6 x 10^-19 C
• Coulomb's Law


  The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them
• Static Electricity


  The build up of an electric charge on the surface of an object, the charge builds up but does not flow, it is potential energy and does not move, it is stored
• Coulomb's law


  Resembles the law of gravity, but gravitational forces are always attractive, whereas electric forces may be attractive or repulsive
• Gravitational forces


  Dominate on a cosmic scale
• Electric forces


  Dominate on an atomic scale
• Ampere


  Measure of how much electrical current is flowing, measured in amps
• Current


  Varies depending on the force behind the current and the resistance to flow
• Electrical Potential Energy


  Energy resulting from the force between two objects having different voltages
• Electrical Energy


  The force behind moving electrons
• Potential Difference


  The electrical potential energy per coulomb of charge, also known as voltage
• Conductors


  Materials through which electric current flows easily
• Insulators


  Materials through which electric current cannot move
• Conductors and Insulators


  • No examples provided
• Resistance


  The opposition to the flow of an electric current, producing heat, the greater the resistance, the less current gets through, good conductors have low resistance
• Ohm's Law


  Resistance is a measure of opposition to the flow of charge and is measured in ohms (Ω)
• What Influences Resistance


  • Material of wire - aluminium and copper have low resistance compared to nickel
  • Thickness - the thicker the wire the lower the resistance
  • Length - shorter wire has lower resistance
  • Temperature - lower temperature has lower resistance (No resistance @ 0 K)
• Series Circuit


  The components are lined up along one path, if the circuit is broken, all components turn off
• Parallel Circuit


  There are several branching paths to the components, if the circuit is broken at any one branch, only the components on that branch will turn off
• Electric Power


  The rate at which an electric current does work, equal to the product of the current and the voltage of a circuit, measured in watts (W), the commercial unit is the kilowatt-hour (kWh)