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More Lessons for High School Physics

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A series of free Online High School Physics Video Lessons.

In this lesson, we will learn

  • electric circuits
  • resistors in series
  • resistors in parallel
  • resistors in series and in parallel

Electric Circuits

Electric circuits are one or more loops of wire which allow current to flow all the way around, usually driven by a battery which maintains a potential difference to keep current flowing. Light bulbs, televisions, anything that uses energy, is called a resistor and slows the flow of energy through the circuit. Ohm's Law is often useful in solving electric circuits. Kirkov's loop law states that if you go all the way around a circuit there is no net potential difference.
Understanding electric currents
Identify the path and direction of current flow in a circuit.
Draw and interpret schematic diagrams of circuits.

Resistors in Series

Resistors in series are successive resistors in which the same current cannot simply go through one resistor. We can add resistors, but it increases the resistance of the whole network. If one resistor goes out, all of the resistors go out. To add currents and determine the resistor series, we add resistor1 + resistor2 + resistor3, etc.
How resistors in series affect current flow.

Resistors in Parallel

Resistors in parallel consist of two separate independent circuits so that when the current reaches a resistor, the current can choose which to go through. Most homes are wired in parallel so that unlike resistors in series not all appliances in our homes have to be turned on for a single one to work. Adding resistors in parallel reduces the overall resistance. The smallest current will go through the largest resistor.
To write all the resistors as a single resistor use the equation
1/(effective resistance) = 1/(resistor 1) + 1/(resistor 2).
The effective resistance is smaller than either of the two individual resistors.
How resistors in parallel affect current flow
Derivation and explanation of Resistors in Parallel

Resistor Circuits

Resistor circuits are resistor networks which combine resistors in series and resistors in parallel. Removing a resistor in parallel increases the current flow through the other resistor in parallel but  decreases the overall current flow. Dimming a resistor in series within a parallel circuit kills an entire branch in parallel, reducing the overall current but increasing the current that goes through the other parallel branch.
How resistor circuits incorporate resistors in parallel and in series.
Electric Circuits: resistors in series and parallel


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