Electricity, Circuits, Voltage and Batteries 17.1

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Electricity,Circuits, Voltage and Batteries17.1
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Objectives

• Define electric current.
• Identify the electric symbols for basic circuit
  elements.
• Use a multimeter to test continuity.
• Identify and construct open, closed, and short
  circuits.
• Define voltage source.
• Distinguish between parallel and series
  arrangements of batteries.
• Construct electric circuits with batteries
  connected in series and in parallel.
• Calculate the combined voltage of batteries
  connected in series and in parallel.

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Physics terms

• electric current
• ampere (A)
• electric circuit
• open circuit
• closed circuit
• short circuit
• voltage
• volt (V)
• battery
• voltmeter

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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.
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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.
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What is a short circuit?
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Assessment

• Which statement below is a correct definition of
  electric current? Electric current is . . .
• the energy of moving electrical charges.
• the flow of electric charges through a wire or
  circuit.
• the number of electrons in a circuit element.
• the attraction between charged particles in a
  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.

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Assessment

• Identify the following circuits

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A reliable source of current

• Prior to 1800, no one knew how to create a steady
  supply of electric current.
• Alessandro Volta was the first to succeed.
• He discovered that placing two different metals
  in an acid or salt solution produced an electric
  current between the terminals.
• He connected multiple voltaic piles together to
  create a battery of them.

Adolphe Ganot, Elementary Treatise on Physics,
1893
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What is a battery?

• A battery is a device that converts stored
  chemical energy into electrical energy.
• Batteries come in many different kinds even
  lemons!

electrical energy
chemical energy
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Reading a battery
Batteries come in many sizes and voltages 1.5,
6, 9, 12 V, for example. Voltage is the electric
potential difference between the two terminals of
a battery. Voltage is measured in volts (V),
named after Volta, the inventor of the battery.
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How is voltage measured?
Voltage is measured using a voltmeter or a
digital multimeter.
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Volts and amps
Current and voltage are the two most important
physical quantities for understanding electric
circuits.

• Current measures the flow of charge through a
  wire.
• Voltage measures the change in electrical
  potential energy per unit of charge.

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A useful analogy

• Charges in a wire are analogous to water in a
  pipe
• Electric current is analogous to the flow of the
  water.
• The battery is analogous to the water pump.
• Voltage is analogous to the change in
  gravitational Ep.

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What is a series connection?
In a series connection, the batteries are
connected one after the other. The positive
terminal of one battery is connected to the
negative terminal of the next battery.
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What is a parallel connection?
In a parallel connection, the same ends of both
batteries are connected together.
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Batteries in Series or Parallel

• To calculate the voltage across batteries
  connected in series or in parallel
• When batteries are connected in series, the
  voltages add together.
• When identical batteries are connected in
  parallel, the total voltage remains the same.

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Why does it work this way?
When these batteries are connected in
series, the voltages add together.
Electric charge (1 coulomb) passing through a 1.5
volt battery gains 1.5 joules of Ep. Passing
through a second 1.5 volt battery gains another
1.5 joules of Ep.
Its like climbing a stairway to the second
floor, then another stairway to the third floor.
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Why does it work that way?
When these batteries are connected in parallel,
the total voltage remains the same.
Electric charge passes through one battery OR the
other. It ONLY gains 1.5 joules of Ep because
each charge ONLY passes through one battery.
Its like climbing either of two stairways from
the first to second floor.
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Assessment

• Which statement below provides a correct
  practical definition of a voltage source? A
  voltage source . . .

• creates an electric potential difference between
  two points in a circuit, such as the two ends of
  a battery.
• provides the electrical potential energy needed
  for a circuit to operate.
• is analogous to the pump in a system of
  circulating water.
• all of the above.

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Assessment

• Identify which circuit has batteries connected in
  series and which has batteries in parallel.

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Assessment

1. Calculate the voltage across the batteries for
   each circuit.

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Assessment

• What does the 1.5 V label on the battery mean?
• The voltage of the positive terminal is 1.5 V.
• The voltage of the negative terminal is 0 V.
• The voltage between the positive and negative
  terminals is 1.5 V.
• All of the above