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11.4 Electric Circuits
*Identify parts of a circuit
*Trace the path of electrons through
two types of circuits
*Compare series and parallel circuits
*Predict how circuits are wired in a
home
Electrical Circuits
What is a circuit?
Suppose you took off for a walk on a path in
the park and after making several twists and turns you
ended your trip at the same place you started but never
once did you back track or retrace your path.
If you made this trip you would have completed a circuit. A pathway that ends where it
started.
Let’s imagine that along your trip you came
upon a bridge over a very deep gorge that had been
washed away by a recent storm. Could you continue
on your walk?
Why?
Electrons trying to move along their path through
an electrical circuit act just like people on a path
through the park. As long as they have a pathway
to travel they will do so but this pathway must lead
them back to where they started.
ELECTRICAL CIRCUITS
Electrons flow through a closed, continuous path
called a CIRCUIT.
-ENERGY
SOURCE
++
TAKS
SWITCH
(breaker)
Parts of an Electrical Circuit
+
-
Switch to close the
circuit
Battery
-e source
Wires
-e pathway
clock
light bulb
Resistance
things which the -e
make work.
Parts of the circuit defined
Dry cell
The dry cell or battery provides a source of electrons
( in other places these may come from a power generating plant.)
Wires provide the pathway for electrons to follow
and find their way back to the battery.
The switch, when opened, prevents electrons from
flowing, when closed provides a closed circuit for
the electrons to find their way to the resistance and
back to the battery.
Parts of a circuit defined
Resistance is any type of object which
requires electrical energy to operate.
You guys getting
the picture?
Types of Circuits
Series Circuit
What do you notice
about the series
circuit and how
electrons
would flow?
What would happen if
one of the light bulbs
burned out? Would the
others continue
to work?
No this would
open the path that
the electrons need
to get back to the
- +
battery.
Some Christmas tree lights are wired in a series circuit.
Types of Circuits (continued)
Parallel Circuits
In a parallel circuit
each part of the
circuit provides
the electrons with
a pathway to get
back to the source
even if one of the
others goes out.
The wiring in our
homes is in parallel
circuits. If one light
bulb goes out in your
house, everything
else still works.
Dry
cell
Electric Power and Safety
Electric Power
I remember hearing
about
that.rate at
You should remember that power
is the
which work is done. So, what is electrical power?
If you said that it is the rate that
electricity does work you are correct.
Calculating Electric Power
Power (P)
Voltage (V)
current (I)
P=VxI
An automobile headlight draws 30 amps from a
12 V battery. How much power does it use?
The watt (W) is the unit
P=VxI
for electrical power.
P = 12V x 30 A
P = 360 W
1W = 1 joule / second
Practice Problems
What is the power of a fan operating at 120 V
and 3 amps?
P=VxI
P = 120 V x 3 A
P = 360 W
Calculating Electrical Energy
Energy (E)
Power (P)
time (t)
E=Pxt
How much energy is required to operate the head
light in the first practice problem for 3 hours?
E=Pxt
E = 360 W x 3 hrs
E = 1080 Wh or 1.08 kWh (kilowatt
hours)
Practice Problem
How much energy would the fan from power
problem #2 require if it were operated for 5h?
E=Pxt
E = 360 W x 5 h
E = 1800 Wh or 1.8 kWh
Electrical Safety
1.
You cannot see it - it will kill you
dead ! ! !
2. Ground wires should be on appliances to prevent
shock from outside the appliance. That is what the
third prong on the plug is.
3. Broken wires should be replaced and appliances
with broken wires should not be used.
4. Electrical appliances should not be used near
water. Water can conduct electricity.
Safety (continued)
5. Do not overload circuits by adding too many
appliances to one plug or cord.
6. Fuses and circuit breakers should be used
to prevent overloads. Do not use fuses above the
recommended amps in circuits.
A few Quiz Questions
11 points
each
1. T or F In order for electricity to flow through
a circuit, the circuit must be open.
2. A _______________is used to open or close a circuit.
3. In a ___________ circuit the electrons have only one path
to get back to their source.
4. Name a common part of a circuit that is resistance.
5. The rate at which electricity does work is called
_____________ ___________.
6. T or F Overloading a circuit may cause a fire.
7. ___________ or ____________ are used to prevent
overloads.
8. ___________ wires are used to prevent electric shock.
9. T or F A battery is a source of electricity.
A few Quiz Questions
11 points
each
1. T or F In order for electricity to flow through
a circuit, the circuit must be open.
switch
2. A _______________is
used to open or close a circuit.
series
3. In a ___________
circuit the electrons have only one path
to get back to their source.
4. Name a common part of a circuit that is resistance.
5. The rate at which electricity does work is called
electric
power
_____________
___________.
6. T or F Overloading a circuit may cause a fire.
breakers
Fuses
7. ___________
or ____________
are used to prevent
overloads.
Ground
8. ___________
wires are used to prevent electric shock.
9. T or F A battery is a source of electricity.
Now that
you have
the The
pieces
of End
the
electricity
puzzle