electric circuits

• Electric Circuits


  • Any path along which electrons can flow
  • Electrons will only flow if the circuit is complete with no gaps
• Open Circuits


  Broken and do not allow the flow of electrons
• Closed Circuits


  Complete and allow the flow of electrons
• Types of Circuits


  • Series
  • Parallel
• Series Circuits


  • All current passing through each device is the same
  • Ohm's Law (I = V/R) applies to the entire circuit, AND each individual device within the circuit
  • If one device in the circuit fails, the entire circuit will fail
• Parallel Circuits


  • Each device connects the same 2 points in the circuit
  • Voltage is the same across each branch
  • The total current in the circuit is the sum of the currents in each branch
  • More parallel branches = less circuit resistance = MORE CURRENT
  • If one device in the circuit fails, the rest of the circuit still functions
• Schematic Diagrams


  Simple diagrams which describe electric circuits and make it easy to draw circuits
• Schematic Diagrams


  • A single cell, light bulb and switch are placed together in a circuit such that the switch can be opened and closed to turn the light bulb on
  • A three-pack of D-cells is placed in a circuit to power a flashlight bulb
• Equivalent Resistance


  The value of the single resistor that would represent the resistance of all of the devices in a circuit
• Combining resistors in a compound circuit

  1. For series circuits: R_eq = R_1 + R_2 + R_3 + ...

  2. For parallel circuits: 1/R_eq = 1/R_1 + 1/R_2 + 1/R_3 + ...
• Parallel Circuits and Overloading

  • Low resistance wires connecting wall outlets to generators at the power utility
  • Usually carry 110 V to 120 V
  • When more devices connected in parallel: Resistance is lowered, Current is increased
  • If this current exceeds the safe amount for the line, the circuit is said to be overloaded
• Fuses


  • Devices connected in series to prevent the overloading of circuits
  • A fuse is constructed of a thin wire that will melt if the current becomes to great, therefore breaking the circuit
• Short Circuit


  • Insulation wears away, causing wires to touch, shortening the circuit
  • This bypasses the normal resistance of the circuit
  • Draws very large currents