Download Electricity and Circuits

Electricity
and
circuits
What is electricity?
Electricity is the flow of electric
charges, typically through wires,
conductors, and electrical devices.
Sometimes we can see the effects
of electricity in nature.
What is electric current?
Electric current is the flow of
charged particles, usually
through wires and circuits.
Current is measured in
amperes (A), also called
amps.
Animated illustration, page 472
How do we measure
electric current?
Electric current is measured using an ammeter
or, more commonly, a digital multimeter.
In order to properly measure current, all the
current must flow into the meter and back out
again, into the circuit being tested.
What is an electric circuit?
An electric circuit is a conducting path
through which electric current can flow.
The symbol for electric current is I.
In this circuit, I = 0.3 amps.
Charge is conserved
Electric current I must be the same
at all points in a simple, single-loop
circuit.
I
Charge can never be created or
destroyed. All the charge that flows
through one point in the circuit must
flow through the next point also.
I
Open and closed circuits
An open circuit does not have a
complete path so no current flows.
A closed circuit has a complete
path, allowing current to flow.
Common circuit elements
Knife blade switches
A knife blade switch uses a
mechanical lever to open/close
a circuit connection.
The handle is an insulator, so
you won’t get a shock when you
touch it!
When attaching a knife blade
switch to a circuit, do so with it
in the open position.
What is a short circuit?
What is a breadboard?
A circuit breadboard is a device used for
mounting and prototyping electric circuits.
Power and ground are connected
from an external source to strips on
the edge of the breadboard.
Exploring the ideas
In Investigation 17A
you will build electric
circuits using a circuit
breadboard.
Investigation
Part 1: Exploring the connections on a breadboard
1. Use the continuity setting on a
multimeter to test whether the
probes are connected to each
other.
2. Identify 3 kinds of connections:
power (red); ground (blue); and
terminal (black).
3. Draw a diagram showing the
connections between the holes
in the breadboard.
Investigation
Questions
a. Where should you connect the
positive and negative terminals
of a battery?
b. Where should you connect
other circuit components, such
as lamps and resistors?
c. How are the holes in a circuit
board connected to each
other?
Investigation
Draw a diagram showing the connections between the holes in the
breadboard on your student assignment sheet.
Investigation
Part 2: Wiring a simple circuit
1. Connect power and ground from a
+3 V voltage source (or 2 D-cells) to
the breadboard.
One lead connects to the
breadboard's power strip; the
other to the ground strip.
1. Connect a simple circuit with one
lamp.
Investigation
Does your lamp illuminate?
If not, check all your connections.
The two ends of the lamp must be
in different rows.
You can use ANY rows.
This example uses rows 9 and 10.
Create a
simple switch
How can you use wires to create a
switch?
Does your lamp go on and off as you
connect/disconnect the switch?
Short circuit
How can you use a wire to
modify your circuit to create
a short circuit?
Short circuit
How can you use a wire to
modify your circuit to create
a short circuit?
Hint: use a wire to bypass the lamp!
What should happen to the
lamp if you create the short
circuit correctly?
Assessment
2. Label each of these electrical symbols with the name of the
electrical component it represents: battery; resistor; lamp; switch;
or wire.
Assessment
2. Label each of these electrical symbols with the name of the
electrical component it represents: battery; resistor; lamp; switch;
or wire.
wire
switch
battery
lamp
resistor
Assessment
4. Identify the following circuits:
Assessment
4. Identify the following circuits:
Short circuit
Open circuit
Closed circuit
Going further
How to strip the plastic insulation off the ends of a wire
A small amount of plastic insulation must
be removed from the ends of wires to use
them in circuits.
If your wires are not “pre-stripped,” then
you will need to use a wire stripper to
remove a small amount of the insulation.