Download Parallel and Series Circuits

Parallel and Series Circuits
1
1
Definitions
2
• 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 (W)
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:
0.5 A
1.0 A
9W
9V
9W
9V
9W
1.0 A
0.5 A
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
3.0 A
• Example:
2.0 A
1A
1.0 A
9W
9V
9W
1A
1A
9V
9W
9W
9V
1A
9W
1.0 A
2.0 A
1A
3.0 A
9W
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: http://www.edugateway.com/sites/tkids/
– 3 & 4: www.nscdiscovery.org/…/ParallelCircuits.htm
• Text:
– Plumb, Donald, et. al. Science 9. Scarborough, ON:
Nelson, 1999. (Chapter 10).