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CURRENT ELECTRICITY
The problem with understanding electricity, is that it’s effects happen too quickly and you can’t see it. For
this reason we use models to understand it. Two models that have been found useful are the Styrofoam
Ball Model, and the Water Model.
Lesson 1:
A Simple Electric Circuit
1
1
LOW
VOLTAGE
POWER SUPPLY
AC
ON
VOLTAGE
ADJUST
O FF
-
DC
VOLTMETER
+
0-6V 5A MAX.
AMMETER
1) In the table below describe what the following parts in the circuit above, do.
Electric Circuit Part
What the parts do.
Battery (or Source)
The battery gives the Coulombs their energy by lifting them to
higher voltage( potential).
Conductor (wires)
The conductor passes the Coulombs along without changing
their energy.
Switch
The switch allows the Coulombs to pass or not.
Insulator
An insulator does not allow all Coulombs to pass.
Ammeter
An ammeter counts the number of Coulombs passing a particular
point every second.
Volt”meter”
The voltmeter measures how much energy the Coulombs lost
while falling through the light bulb or gained while raised through
the battery.
Light Bulb
The light bulb changes the Coulombs electrical energy into heat
and light energy.
2) In order to connect a ammeter to a circuit you must break the circuit and insert the meter.
3) In order to connect a voltmeter to a circuit you measure around the circuit component.
4) What is a circuit?
A circuit is the path that the Coulombs of electrons take.
5) Fill in the table below
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Type Of Meter
Physical Quantity Measured
Unit Of
Measurement
Relationship To Other
More Fundamental
Units
Ammeter
current
Ampere (Amp)
Coulombs
second
Voltmeter
energy level
Volt
Joules
Coulombs
6) A Light Bulb, Motor, Electrical Heater, Radio can all be referred to as a load.
7) What does our model predict about where can a switch be placed in our circuit?
Our model predicts that a switch can be placed anywhere in the circuit.
8) What is current?
Current is the number of Coulombs flowing pass some point in the circuit.
9) What does our model predict about the amount of current flowing through different points in our circuit?
Our model predicts that the amount of current flowing anywhere in the circuit will be the same.
10) What is voltage?
Voltage is the amount of energy each Coulomb gains as it “is raised in the source”
or releases as it “falls through a load” in the circuit.
11) What does our model predict about the voltage gain at the source compared to the voltage drop across the
light bulb?
Our model predicts that the voltage gain at the source will be the same as the voltage drop across
the light bulb.
12) What is a short circuit?
A short circuit is a very easy path for the electrons to flow around the light bulb. This might
actually be a longer path in distance but easier path for the Coulombs to fall.
13) What does our model predict will happen in a short circuit?
Our model predicts that the Coulombs electrons will flow very rapidly in a short circuit . This will
cause the wires conducting the Coulombs to heat up.
14) What actually happens to the current in a short circuit?
The conducting wires really do heat up.
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Schematic Diagrams
A Schematic Diagram is a short hand system for drawing an electric circuit. In order to simplify the
diagrams, symbols are used instead of pictures and conductors are represented with horizontal or vertical
lines.
1) Complete the table below with the names for the schematic symbols shown.
Schematic Symbol
-
Part Name
+
cell or source of electrical energy.
switch
light bulb
fuse
A
ammeter
V
voltmeter
2) Draw the Schematic Circuit Diagram for the circuit below. Remember conductors are represented with
horizontal or vertical
lines.
Circuit Picture
LOW
VOLTAGE
POWER SUPPLY
AC
ON
OFF
VOL T AGE
ADJUS T
-
DC
VOLTMETER
+
0-6V 5A M AX.
AMMETER
Schematic Circuit Diagram
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REALITY CHECK - Wiring Real Circuits
Models and theories are useful in explaining and predicting what happens in real circuits. But they must be
checked to ensure they are always useful. Unfortunately wiring real electric circuits from schematics can
be difficult. There are a few tricks that will help.
Trick #1
Place all the circuit parts in the same relative position that they are in the schematic
diagram. This will help you locate where to connect the different meters later.
Practice comparing locations on the schematic and real circuits with the pictures below
B)
A)
B)
LOW
VOLTAGE
POWER SUPPLY
AC
ON
OFF
VOL T AGE
ADJUS T
-
DC
VOLTMETER
+
0-6V 5A MAX.
D)
A)
C)
C)
D)
AMMETER
1) Label all the points indicated on the schematic diagram on the circuit picture.
C)
B)
LOW
VOLTAGE
POWER SUPPLY
B)
D)
C)
D)
AC
ON
DC
-
VOLTAGE
ADJUST
OFF
VOLTMETER
+
0-6V5AMAX.
A)
A)
AMMETER
2) Label all the points indicated on the circuit picture on the schematic diagram.
Trick #2
!
Trick #3
!
!
Connect the ammeter when connecting the rest of the circuit because it is ”in line” with
other circuit parts
Connect the voltmeter last. Since the voltmeter is connect “around” other circuit parts
leave it until the last
If the light bulb does not light when the switch is closed, there are a number of things you
should do.
Check the bulb to make sure it is screwed in tightly and not burned out
Check all connections to see if they are loose by gently shaking them. Sometimes loose
connections act like little open switches that you can not see.
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Wire the circuits shown and complete the table.
Circuit Picture
Schematic Diagram
These values should all be
the same
Ammeter
Voltmeter
These values
should all be the
same
L OW
VOL T AGE
P OW E R S UP P L Y
AC
ON
VOLTAGE
ADJ UST
OFF
-
DC
V
VOLTMETER
+
0-6V 5A MAX.
A
AMMETER
L OW
VOL T AGE
P OW E R S UP P L Y
AC
ON
VOLTAGE
ADJ UST
OFF
-
DC
V
VOLTMETER
+
0-6V 5A MAX.
A
AMMETER
A
AMMETER
LOW
VOL TAGE
P OW E R S UP P LY
V
AC
ON
VOLTAGE
ADJ UST
OFF
-
DC
VOLTMETER
+
0 -6 V 5 A M AX.
A
AMMETER
LOW
VOLTAGE
P OWER S UP P LY
V
AC
ON
OFF
VOLTAGE
ADJ UST
-
DC
VOLTMETER
+
0 -6 V 5 A M AX.
L OW
VOL T AGE
P OW E R S UP P L Y
AC
ON
OFF
VOLTAGE
ADJ US T
-
DC
V
+
0-6V 5A MAX.
VOLTMETER
AMMETER
A
Complete these statements.
1) In these circuits, the amount of current measured anywhere in the circuit is about the same .
2) In a circuit containing ONE bulb, the voltage drop across the bulb is about
across the source.
the same as the voltage gain
3) In these circuits, a switch placed anywhere will control the light bulb.
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