Transcript Series and Parallel Circuits

Warm Up
1.
What color absorbs ALL colors of the visible
light spectrum?
2.
What color reflects ALL colors of the visible
light spectrum?
3.
Where does light travel fastest?
4.
Where does light travel slowest?
5.
We see different colors because objects
reflect different _______________ of light.
a)
b)
c)
Amplitudes
Wavelengths
Speeds
Series and
Parallel Circuits
resistance
is the measure of how
difficult it is for charges to flow through a
material
Ohm
unit: (Ω)
current
is the amount of charge that
passes
by a point
in a second
Ampere,
amp,
unit:A
voltage
-the difference in electrical
potential energy between 2 places in a circuit; it
is the energy
volt, Vthat pushes charges through a
circuit
unit:
Objectives
•
Name the three essential parts of a
circuit.
•
Compare series circuits with
parallel circuits.
•
Explain how fuses and circuit
breakers protect your home against
short circuits and circuit overloads.

Compare motors and generators
Electric Circuits
•
An electric circuit is a
complete, closed path through
which electric charges flow.
•
All circuits have three basic
parts:
•
•
•
Energy source
Wires
Load
•
Energy source examples:
•
•
•
•
•
Loads change electrical energy to other
forms of energy
•
•
Battery
Generator
power plant (coal, nuclear, gas)
hydroelectric plant
Examples: lightbulb, television, toaster
Wires are made from conductive materials
(i.e., copper)

A switch is used to open and
close a circuit.

When the switch is open, electrical
current CANNOT flow
Brain Pop: Electric Circuits
Circuits
 Can
either be series or
parallel or a combination of
the two.
Series
Current
only takes
one path for
electrons
Current flows
through every part of
the circuit
Lights in a Series
Series
If
you add a resistor (like
another light):
Total
resistance goes UP
since all the current has
must go through each
resistor.
Adding Resistors to
Series:
Current in the circuit
will go DOWN (lights
will dim)
If you remove a light
bulb or one burns
out—all go out!
Resistance in Series
Add
up all resistors to
get total resistance
Total
resistance will go
up because all of the
current must go through
each resistor.
Calculating
Resistance Example:

If the resistances
of loads R1, R2,
and R3 are 10Ω,
20Ω & 30Ω
respectively, what
is the total
resistance in the
circuit?
Current in Series
Current
is the same at
all points
Use Ohm’s Law to find
current using
resistance and voltage
Calculating Current
Example:
If the resistances of
loads R1, R2, and R3
are 10Ω, 20Ω & 30Ω
respectively, and the
voltage source is 6 V,
what is the current
through the circuit?
Voltage in Series
Voltage
is
reduced by each
resistance –
voltage drop
Calculating Voltage
Example

Using the current
that you calculated
in the previous
problem, what is the
voltage difference
(drop) across each
resistor?
Sample Problem #1

1.
2.
3.
Draw a series circuit with two 1.5 V
batteries, 3 resistors, and a current
of 0.5 A.
What is the total voltage of the
circuit?
What is the resistance of each
resistor?
What is the voltage drop across each
resistor? Label it on your circuit.
Parallel Circuits
Have
at least one point
where current divides
More than one path for
current to flow
Paths are also known as
branches
Lights in Parallel
Parallel:
If
you add a resistor:
Total resistance goes
down
Total current goes up
when you add
another path
Removing a Light
Bulb
If
you remove a light
bulb or one burns out,
the others stay on
because the circuit is
still closed.
Current in Parallel
Current
flows into a
branching point, the
same total current must
flow out again
Current depends on
resistance in each
branch
Calculating Total Resistance in a
Parallel Circuit


Kirchoff’s Law of Currents states
that the sum of the currents in must
equal the sum of the currents out.
The formula for calculating total
Resistance, RT:
Current in Parallel
Calculate
current in
each branch based on
resistance in each
branch by using
Ohm’s Law
Calculating Current
Example:

If the resistances of
loads R1, R2, and R3
are 10Ω, 20Ω & 30Ω
respectively, what is
the total resistance in
the circuit?
Voltage in Parallel
Voltage
is the
same across each
branch – because
each branch is on
the same wire
Calculating Voltage
Example:

If the voltage
source is 6 V, what
is the voltage
difference (drop)
across each
resistor?
Practice problem #2

1.
2.
Draw a parallel circuit with a 6
ohm & a 18 ohm resistor (one
on each branch) and a 12 V
battery.
What is the voltage through
each resistor?
What is the current flowing
through each branch?
Toll Road—Circuit
Analogy
Toll Booth
Explanation
 Adding
toll booths in series
increases resistance and
slows the current flow.
 Adding toll booths in
parallel lowers resistance
and increases the current
flow.
Batteries in Series
and Parallel:
In
series—The voltage
is increased.
In parallel—No
change in voltage;
these batteries will
last longer!
One More FINAL
Thing:
Two
Types of Current:
DC—Direct Current—
produced by solar cells
and chemical cells
(batteries)
Current only flows in
one direction.
nd
2 type of current:
AC—Alternating
Current
Current flows back and
forth (alternates)
Found in homes
Generators produce AC
current

Too many loads or too much
voltage can be dangerous


fuse -thin strip of metal that melts
and opens circuit
circuit breaker – sometimes a piece
of metal that bends, thus opening the
circuit


Generator – converts mechanical to
electrical energy
Motor – converts electrical to
mechanical energy
When Andre plugs his stereo into the same
outlet as the television and lamp, all three
won’t work. What is the most likely
hypothesis for what happened?
A The circuit was overloaded, and the circuit
breaker opened.
B The circuit was complete, and the circuit
breaker closed.
C Only the stereo operates on alternating
current.
DThe stereo’s electrical cord was faulty.
Suki can have all five appliances in her
kitchen on at the same time, or she
can have each appliance on one at a
time. How are the appliances in Suki’s
kitchen wired?
Ain a single loop
Bin a direct current circuit
C in a parallel circuit
D
in a series circuit