Two circuit handouts

Period: I Circuits and Symbols [
Ch. 6:2
Electricity works a lot like
water. Often knagining how
water would work in an
ckcuit wilt tell you how
electricity will work as well.
Electricity flows through circuits: paths of conductors (usually wires),
Any break in the circuit will cause the circuit to fail, just like a break in
a pipe lets water leak out of a water system.
A closed
circuit has
no breaks:
the light
lights up.
An open
circuit has a
break in it:
the light
will not
light up.
A break in a circuit
is any spot where
an insulator is in
the way of the
electricity’ s flow.
Paper, plastic, or
even an air gap
can keep electricity
from flowing~
I
Circuit diagrams are a short-cut method of drawing
circuits. They don’t need to be perfectly draw,
but they can be drawn wrong.
Circuit diagrams
Electrical Symbols
bakery
[ capacitor
These components look similar, but are
very different and have different functions.
wire
battery
-T-
~aths for electricity
to flow.
pushes electricity
through circuit.
pipes
pump
light bulb
light bulb
lights up; resists
electricity.
equivalent
switch
switch
turns electricity
on and off
valve
The diagram on the right is a faster way of
drawing the circuit on the lefk (Notice the
direction of the battery, which is important)
resistor
resists flow of
electricityl
restriction
in a pipe
Voltage Pushes Electrons
The ends of a battery
are oppositely
charged. This
creates a force,
pushing electrons
thrOagh the circuit.
3 Quantities of a Circuit
The flow of electrons we call current
which travels through closed circuits,
Resistance Resists Current Flow [
Devices in the circuit do work, which
slows down (restricts) current.
Circuit
continues
Voltage is measured in Volts. Current is measured in Amps. Resistance is measured in Ohms.
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These three quantities are lk~ed in any circuit.
Change one of them and one or both of the others will change.
Copyright © 2004, C. Stephen Murray

Period:
Types of Circuits and Ohm’s Law
Ch.7:1
Series circuits have all only one
path for the electricity to flow.
Two lightbulbs in series,
Each light is dependent
on the other.
If any part of a series
circuit is broken, the
circuit fails. If either
light is unscrewed both
lights will turn off.
The branches (paths)
of a parallel circuit are
independent. If either
light is unscrewed, the
other will remain on.
Your house is wired in parallel, so that each light and
appliance can be turned on and off independently.
Parallel circuits have multiple
paths for the electricity to flow.
Two lightbulbs in parallel.
Each light is independent
of each other.
Ohm’s Law I
Voltage
V ~ (in volts)
Current ~ | __~
(in amps)-- ~" --
R ..~._._ Resistance
(in ohms)
Current equals the voltage
divided by the resistance.
Also, V = IR and R = V/I
Abbreviations:
A - Amps - current
v - volts - voltage
~ - ohms - resistance
Increasing voltage
increases current
Increasing resistance
decreases current,
Decreasing voltage
decreases current
Decreasing resistance
increases current.
Ex. How much current does a 12 v
battery push through a 3 ~ resistor
V = 12v
~_=3~
I=
I=V = 12v @
R 3~
Ex. How strong a batteryproduces
2 A through a 3 D resistor
V=v i=~
V So, V= IR
R=3D R = (2A)(3a)
I=2A
Current
Voltage
J
I Resistance I
Current is moving electrons,
moving charge.
Increasing current causes
more electricity to move
through a device.
Increasing electricity through
a device causes it to work
faster (in a motor) or be
brighter (in a lighthulb).
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Using Otma’s
Law: I = V/R
Using Ohm’s
Law:I = V/R
More current =
brighter light.
Voltage is electrical potential:
how much work a battery can do.
Voltage is linked to energy:
I volt of voltage = 1joule of energy
per coulomb of charge
To increase voltage you could use a
stronger battery OR add batteries.
~
1.Sv~
9volts 1.5 v U 3 volts
total
More voltage is like a
stronger pump, giving more
force and more current.
0 volts total
The lightbulb doesn’t
light here, because
the two batteries are
pushing opposite
directions. To add
together, batteries
must be facing the
same direction.
Resistance slows down current.
Third( of resistance like
a dam holding back water.
Adding devices in a circuit
increases resistance.
I = V/R
= 6v/3~ = 2 A
The light is bright
because the 6
volts only have
one light to ran.
I = V/R
~
_~_x~ = 6v/6~ = 1 A
Both lights are
dimmer because
the 6 volts have
two lights to run.
More resistance = less current
Less current = less fight
Copyright © 2004, C. Stephen Murray