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Section Summary

PhysicsSection Summary

19.1 Ohm's law

  • Direct current is constant over time; alternating current alternates smoothly back and forth over time.
  • Electrical resistance causes materials to extract work from the current that flows through them.
  • In ohmic materials, voltage drop along a path is proportional to the current that runs through the path.

19.2 Series Circuits

  • Circuit diagrams are schematic representations of electric circuits.
  • Resistors in series are resistors that are connected head to tail.
  • The same current runs through all resistors in series; however, the voltage drop across each resistor can be different.
  • The voltage is the same at every point in a given wire.

19.3 Parallel Circuits

  • The equivalent resistance of a group of N identical resistors R connected in parallel is R/N.
  • Connecting resistors in parallel provides more paths for the current to go through, so the equivalent resistance is always less than the smallest resistance of the parallel resistors.
  • The same voltage drop occurs across all resistors in parallel; however, the current through each resistor can differ.

19.4 Electric Power

  • Electric power is dissipated in the resistances of a circuit. Capacitors do not dissipate electric power.
  • Electric power is proportional to the voltage and the current in a circuit.
  • Ohm’s law provides two extra expressions for electric power: one that does not involve current and one that does not involve voltage.
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