electric potential

• 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, EPL are also drawn around the charge to represent the electric potential around it
  • It also describe the characteristic of the respective charges and the surfaces bearing electrostatic potential
• Applications


  • 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  • Outdated by technology but still used in laboratories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


  • Voltage is equal to the current multiplied by the resistance
  • V=IR
• Ohm's Law Examples


  • If you want to find Voltage in Volts: V = IR
  • If you want to find Resistance in Ohm's: R = V / I
  • If you want to find Current in Amps: I = V / R
• Voltage and Current


  • If the voltage in a circuit increases, the current will increase
  • If the voltage in a circuit decreases, the current will decrease
  • This is a direct/proportional relationship
• Resistance and Current


  • If the resistance in a circuit increases, the current will decrease
  • If the resistance in a circuit decreases, the current will increase
  • This is an inversely proportional relationship
• 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