ohm's law

• Potential Energy


  Energy at rest
• Gravitational Potential Energy


  Potential energy due to a body's elevation from the ground
• Electric Potential


  A quantity of energy possessed by a point charge at a given location in space
• Electric Potential


  • Represented by "VE"
  • Amount of electric potential energy per unit charge
  • Mathematically described as: VE = kQ/r or VE = U/q
  • Unit: J/C or Volt
• Equipotential Lines


  • Like electric field lines, they are also drawn around the charge to represent the electric potential around it
  • They also describe the characteristic of the respective charges and the surfaces bearing electrostatic potential
• EG in CRT TV Picture Tubes

  • Electric charges with computed potentials are rushed into the CRTs to form distinct images on the TV screens
• Van de Graff Generators

  • Developed as particle accelerators
  • Outdated by technology but still used in laboratories
• Voltage


  • The charge (electron) "pusher." Voltage causes current to flow/move.
  • Voltage sources: Battery, Generator, Outlets
  • Symbol for voltage = V
  • Unit for voltage = Volts (V)
• Current


  • Flow of charge (electrons) within a conductor or how fast charge is moving
  • Symbol for Current = I
  • Mathematically: I = q/t
  • Unit for Current = Amperes (A) or C/s
• Resistance


  • Opposes the push from the voltage source. Resistance affects the speed of the current.
  • Limitation to current flow
  • Symbol for Resistance = R
  • Mathematically: R = ρL / A

  ρ is the material's resistivity

  L is the length of the material

  A is the cross-sectional area

  • Unit for Resistance = Ohms (Ώ)
• Resistivity


  A material property

  Dependent on the number of free or mobile charges (usually electrons) in the material

  In a metal, this is the number of electrons from the outer shell that are ionized and become part of the 'sea of electrons'

  Dependent on the mobility of the charges

  Mobility is related to the velocity of the charges. It is a function of the material, the frequency and magnitude of the voltage applied to make the charges move, and temperature.
• Resistivity of Common Materials at Room Temperature

  • Silver: 1.64x10-8 Ω-m (Conductor)

  Copper: 1.77x10-8 Ω-m (Conductor)

  Aluminum: 2.8x10-8 Ω-m (Conductor)

  Gold: 2.45x10-8 Ω-m (Conductor)

  Carbon (Graphite): 4x10-5 Ω-m (Conductor)

  Germanium: 0.47 Ω-m (Semiconductor)

  Silicon: 640 Ω-m (Semiconductor)

  Paper: 1x1010 Ω-m (Insulator)

  Mica: 5x1011 Ω-m (Insulator)

  Glass: 1x1012 Ω-m (Insulator)

  Teflon: 3x1012 Ω-m (Insulator)
• Ohm's Law


  V=IR

  Voltage is equal to the current multiplied by the resistance.

  Voltage, measured in Volts, V

  Current, measured in Amps, A

  Resistance, measured in Ohms, Ω
• If the voltage in a circuit increases


  The current will increase
• If the voltage in a circuit decreases


  The current will decrease
• If the resistance in a circuit increases

  The current will decrease
• If the resistance in a circuit decreases


  The current will increase
• Resistors


  All electronic devices which represent a load in an electronic circuit can be modeled as a resistor

  A resistor is a device which contains a defined amount of resistance and is used to control current in an electronic circuit
• Electric Circuits


  The pathway for the current to move to and from the source and the appliance

  Closed Circuit: Allow the current to flow from the source to the load where current is needed

  Open Circuit: Have gaps where current can't flow
• Series Circuit


  All components are connected using a single pathway

  Formulas: Vtotal = V1 + V2 +V3 +… + Vn

  Rtotal = R1 + R2 + R3 + … Rn

  Itotal = I1 = I2 = I3 = … = In
• Parallel Circuit


  Use branches to allow current to pass through more than one path

  Formulas: Vtotal = V1 = V2 = V3 = … = Vn

  1/Rtotal = 1/R1 + 1/R2 + 1/R3 + … 1/Rn

  Itotal = I1 + I2 + I3 + … + In
• Ohmic Components


  Show the relationship between V and I

  Examples: Resistors and Conducting Wires
• Non-ohmic Components


  Ohm's law does not apply in the way these components operate

  Examples: Transistors and diodes
• ALESSANDRO VOLTA

  
• ANDRE AMPERE

  
• GEORGE OHM