p6 pre-finals

• Potential


  Something is about to happen
• Types of Potential Energy

  • 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
  • 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
• Computing electric potential from a source charge

  • Compute the electric potential from a source charge of 5.02 x 10-13 if a test charge will be placed 2.08 x 10-3 away from it
• Determining source charge of an electric potential

  • Determine the source charge of an electric potential of 2.78 x 103 Volts which is 3.02 x 10-2 m
• 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 of Electric Potential

  • CRT TV Picture Tubes
  • Van de Graff Generators
• Voltage


  The charge (electron) "pusher". Voltage causes current to flow/move
• Voltage sources


  • Battery
  • Generator
  • Outlets
• Current


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


  • Opposes the push from the voltage source
  • Affects the speed of the current
  • Limitation to current flow
  • Mathematically: R = pL/ A
  • Unit for Resistance = Ohms (Ώ)
• Resistivity


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

  • Silver: 1.64x10-8 W-m (Conductor)
  • Copper: 1.77x10-8 W-m (Conductor)
  • Aluminum: 2.8x10-8 W-m (Conductor)
  • Gold: 2.45x10-8 W-m (Conductor)
  • Carbon (Graphite): 4x10-5 W-m (Conductor)
  • Germanium: 0.47 W-m (Semiconductor)
  • Silicon: 640 W-m (Semiconductor)
  • Paper: 1x1010 W-m (Insulator)
  • Mica: 5x1011 W-m (Insulator)
  • Glass: 1x1012 W-m (Insulator)
  • Teflon: 3x1012 W-m (Insulator)
• Ohm's Law


  • Relationship between current, voltage, and resistance
  • Voltage is equal to the current multiplied by the resistance
• Ohm's Law Examples

  • If I= 2 A and R = 5 Ohms, then V= (2A)(52) = 10 V
  • If V = 9 Volts and I = 4 A, then R = 9 V/ 4A = 2.25 Ω
  • If V= 140 V and R = 22 Ω, then I = 140V/ 20 = 70 A
• 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
• 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
• 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
• Classification of Circuit Components

  • 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