Electricity and circuits

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Electricity andcircuits
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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.
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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
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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.
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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.
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Charge is conserved
I
Electric current I must be the same at all points
in a simple, single-loop circuit. 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
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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.
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Common circuit elements
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Knife blade switches
A knife blade switch uses a mechanical lever to
open/close a circuit connection. The handle is
an insulator, so you wont get a shock when you
touch it! When attaching a knife blade switch to
a circuit, do so with it in the open position.
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What is a short circuit?
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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.
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Exploring the ideas
In Investigation 17A you will build electric
circuits using a circuit breadboard.
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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.

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Investigation
Questions

1. Where should you connect the positive and
   negative terminals of a battery?
2. Where should you connect other circuit
   components, such as lamps and resistors?
3. How are the holes in a circuit board connected to
   each other?

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Investigation
Draw a diagram showing the connections between
the holes in the breadboard on your student
assignment sheet.
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Investigation
Part 2 Wiring a simple circuit

• Connect power and ground from a 3 V voltage
  source (or 2 D-cells) to the breadboard.
• Connect a simple circuit with one lamp.

One lead connects to the breadboard's power
strip the other to the ground strip.
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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.
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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?
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Short circuit
How can you use a wire to modify your circuit to
create a short circuit?
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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?
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Assessment

1. Label each of these electrical symbols with the
   name of the electrical component it represents
   battery resistor lamp switch or wire.

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Assessment

1. 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
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Assessment

• Identify the following circuits

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Assessment

• Identify the following circuits

Short circuit
Open circuit
Closed circuit
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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.
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