Parallel and Series Circuits 1 1

Definitions Voltage (V) –electric potential, measured in volts (V) Electric Current (I) –a measure of the rate at which electric charges flow, measured in Amperes (A) Resistance (R) –the ability to impede the flow of electrons in conductors, measured in Ohms (  ) 2

Electrical Resistance & Ohm’s Law Potential difference: the loss of electric potential caused by resistance as electric current flows through a conductor (also called voltage drop) Ohm’s Law: the potential difference between two points on a conductor is directly related to the electric current flowing through the conductor –Formula : V = I x R Ohm’s Law applies only to electrical loads that do not change resistance with temperature

The Series Circuit Series Circuit –an electric circuit in which the electrical loads are wired to one another in a single path A string of Christmas lights is an example of a series circuit; when one burns out the circuit is broken and none of the lights will work. 3

Series Circuit with Multiple Loads If the resistance in a series circuit is increased, then by Ohm’s law, the current will decrease. Example: 1.0 A 9 V 9  0.5 A 9 V 9 

Characteristics of a Series Circuit Total resistance in a series circuit increases as each load is added Electric current is the same throughout all parts of a series circuit Current in a series circuit will stop flowing if the path of the current is interrupted at any point

The Parallel Circuit Parallel Circuit –an electric circuit in which each electrical load is connected to the energy source by its own separate path or branch circuit Branch Circuit –a separate circuit through which current passes to each load in a parallel circuit 4

Parallel Circuit with Multiple Loads Adding a branch circuit to a parallel series allows the same amount of current to flow through each path The voltage drop is the same for each branch circuit so the current will increase with each load Example: 9 V 1.0 A 9  3.0 A 1 A 9  9 V 1 A 9  2.0 A

Characteristics of a Parallel Circuit The total current flowing from the source of electrical energy is equal to the sum of the branch circuits Adding another load will cause the total current to increase Separate branch circuits can be used without affecting any of the others (example: using the toaster but not the coffee-maker)

Combination of Series and Parallel Circuits Electric circuits often have parallel and series circuits put together Example: –When you turn on a set of three light bulbs, you use two switches: one is a safety switch on the main electrical control panel, and the second is the switch on the wall. Those are the parallel circuits. The series circuit is the set of three light bulbs.

Sources Pictures: Retrieved Feb. 3, 2003 from... –1: whyfiles. larc.nasa.gov/…/electricity/circuits2.html –2: –3 & 4: Text: –Plumb, Donald, et. al. Science 9. Scarborough, ON: Nelson, (Chapter 10).