Physics 2- Q3

• Static electricity


  Electricity at rest produced when there is an imbalance of electrical charges
• Electron


  Negatively charged particle discovered by JJ Thomson
• Proton


  Positively charged particle discovered by Ernest Rutherford
• Coulomb


  Unit of electric charge
• Charge separation


  Occurs when an external charged sphere is placed near the neutral sphere
• Subatomic particles that make up atoms

  • Electrons
  • Protons
  • Neutrons
• Net charge


  The sum of the number of electrons and protons in an object
• Charging by friction


  Electrons are transferred when objects are rubbed against one another
• Electron affinity


  The chemical property of an atom to attract electrons
• Triboelectric series


  Ranks materials based on their tendency to acquire charge
• Charging by conduction


  Also known as charging by contact, a charged object is touched to a conductor
• The law of conservation of charge states that the algebraic sum of all the electric charges in any closed system is constant
• Types of charges


  • Positive
  • Negative
• Methods of charging an object

  • Charging by friction
  • Charging by induction
• Coulomb's law


  The magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them
• Free-body diagram


  Diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation
• Superposition of forces


  When more than two charges are present, the resultant force on any one of them equals the vector sum of the forces exerted by the various individual charges
• Electric field


  The amount of electric force on a charged body exerted by external charged bodies
• Electric field lines


  • Emanate from positive charge and terminate to negative charges
  • Do not intersect at one point, only meet when there is an attractive force
  • The density of the lines represents the strength of the field
• Linear charge density


  For a line charge distribution, unit is C/m
• Surface charge density


  For a distribution over a surface, unit is C/m^2
• Volume charge density


  For a distribution through a volume, unit is C/m^3
• Electric flux


  The "rate of the flow of the electric field," as determined by the number of electric field or flux lines passing through a given region
• A positive charge within a region will have an outward electric flux passing through its surface, whereas a negative charge will have an inward electric flux traversing its surface. A zero charge contains no electric flux.
• The net electric flux going outward the surface of the region is directly proportional to the magnitude of the net charge enclosed by that region
• Gauss's law


  The mathematical relationship between charges, electric field, and electric flux
• Gauss's law states that in any closed surface, the electric flux is equivalent to the net charge inside the closed surface divided by ε0, which is the electric constant that establishes the direct proportionality between field intensity and electric displacement in a given region.
• Variations of Gauss's law


  • Gauss's law postulates that the total electric flux passing through a closed surface is considered zero unless the volume enclosed by this surface contains a net charge
  • The "enclosed surface" pertained to in Gauss's law is usually imaginary, hypothetical, or arbitrary, commonly called "Gaussian surface"
  • The equation of Gauss's law basically states that the total electric flux passing through a closed surface is proportional to the net electric charge inside this closed surface, divided by the electric permittivity of free space, ε0
• Gauss's law is most beneficial when there is a symmetrical charge distribution, such as a sphere, cylinder, or plane
• Field of a uniform line charge


  The electric charge is uniformly distributed along a long line, such as a wire, and the whole charge present on the line contributes to the field at any point
• For any given point charge, or any spherical charge distribution, use the formula for spherical symmetries. For a uniform line charge, use the formula for cylindrical symmetries.
• Gauss's Law


  The electric flux through a closed surface is proportional to the net electric charge inside this closed surface, divided by the electric permittivity of free space, ε0
• Gauss's Law


  • Most beneficial when there is a symmetrical charge distribution
  • Applicable for spherical, cylindrical, and plane charge distributions
• Calculating electric field using Gauss's Law


  1. Determine the symmetry of the charge distribution

  2. Choose the appropriate Gaussian surface

  3. Apply Gauss's Law to calculate the electric field
• Calculating charge distribution using Gauss's Law

  1. Determine the symmetry of the electric field

  2. Choose the appropriate Gaussian surface

  3. Apply Gauss's Law to calculate the charge distribution
• Spherical charge distribution


  Use the formula for spherical symmetries
• Uniform line charge


  Use the formula for cylindrical symmetries
• Gauss's Law states that in any closed surface, the electric flux is equivalent to the net charge inside the closed surface divided by ε0
• Gauss's Law can be used to: (1) calculate the electric field if the charge distribution is provided, and (2) calculate the charge distribution if the magnitude of the electric field is given
• For any given point charge, or any spherical charge distribution, i.e., the charge is distributed in a uniform manner on the surface, you may use a spherical enclosed surface, or spherical Gaussian surface, where the radius R is centered on the region