10.2 Electric Circuits

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10.2 Electric Circuits
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10.2 Electric Circuits
Some definitions Electric Current the
movement of electric charges from one place to
another. Electric Circuit a controlled path
for the electric current to pass through.
Electric circuits convert electrical energy
into other forms of energy. Examples of
converted electrical energy -
light - heat - mechanical -
sound
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Parts of an Electric Circuit
1.Source of Electrical Energy makes the
electrical energy. 2. Electrical Load
converts electrical energy into the form of
energy needed.
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• Electric Circuit Control Device
• a switch that turns electricity on and off
• Connectors
• the conducting wires that make the controlled
  path for electric current to flow to each part of
  the circuit.

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Types of Circuits
Closed Circuit a circuit that is closed or
on, allowing electricity to flow
through. Open Circuit a circuit that is
open or off, not allowing electricity to
flow through.
An electric current flows in a continuous
loop from negative terminal of the cell through
the wires electric load (light) the switch
Back to the cells positive terminal.
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Electric Circuit Diagrams and Symbols Symbols
are used to simplify the drawing of electric
circuits.
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10.7 Cells in Series and Parallel (page 310)
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10.7 Cells in Series and Parallel

• A dry cell is another term for a battery.
• Dry cells can be put together in two ways to
  change the energy they give each electron as it
  travels through the battery and out the negative
  terminal
• In a series circuit (so they have more power)
• In a parallel circuit (so their power lasts
  longer)

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Cells in a Series
Connecting cells in series increases the electric
potential (voltage) produced at the negative
terminals of the batteries. As the electron
travels through each battery, it gets an
additional boost of energy increasing its
voltage. When an electron leaves the negative
terminal of a battery and enters the positive
terminal of the next battery it picks up more
voltage. The electron exits the negative
terminal of the battery and now has double the
voltage .
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Cells in Parallel
The cells are connected side by side (in
parallel) to increase the electric charge. The
electrons flow through only one cell before
passing through the load. The electric potential
(voltage) of the electron doesnt increase like
it does in a series circuit. But With two
cells there is twice as much electric energy
available and the load can operate twice as long
before running out of energy.
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Series Circuits and Parallel Circuits
Series Circuit This circuit is wired in one
single path. Ex Christmas lights If one bulb
burns out, all the lights have to be checked to
find the burned out bulb.
Parallel Circuit The electrons pass through
separate circuits called branch circuits.
Because each bulb is connected to its own
branch circuit, it does not affect the other
bulbs.
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Series Circuits
Parallel Circuits
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Voltage, Current, Resistance, Ohms Law
10.9, 10.10
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Measuring Electrical Current
Shocks from electric circuits are very serious
compared to shocks from static electricity. Surpr
isingly small amounts of electric current are
lethal.
An electric current is - the rate at which
electric charges move past a given point in a
circuit. The strength of the current is measured
in Amperes (A) The symbol for
current in Ohms formula is I
Current (I) is measured with an ammeter.
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ELECTRIC POTENTIAL VOLTAGE (V)
A volt is a measure of electrical pressure and
is named after the Italian scientist Alessandro
Volta. The energy of each electron is called
the electric potential. Electric potential is
called voltage. A Voltmeter is used to measure
voltage. The symbol for this unit is V.
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RESISTANCE (R)
The molecules of all types of conductors impede,
or resist, the flow of electrons to some
extent. This ability to impede the flow of
electrons in conductors is called electrical
resistance (R).
The resistance to the passage of electric current
is measured with the ohmmeter. The unit is the
ohm O, named after the German scientist George
Ohm. INSULATORS have a high
resistance. CONDUCTORS have a low
resistance.
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OHMS LAW
George Ohm figured out a basic law for
electricity V Volts (electrical
potential) also called voltage drop I
Amperes (current) R Ohms (resistance)
O V I x R I V / R R
V / I
Ohms Triangle
Increasing (?) the voltage increases (?) the
current. As resistance increases (?) the
current decreases (?).
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Measuring Electrical Energy
11.2
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Measuring Electrical Energy
Energy -the ability to do work Electrical
Energy - energy transferred to an
electrical load by moving electric charges.
(symbol is E) Joule (J) - unit for
measuring energy. Because a joule is so small,
energy is also measured in much larger units such
as the watt hour and the kilowatt hour.
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Calculating Electrical Energy
Electrical Energy Voltage x Electrical
Current x Time Interval E V
x I (amps) x change
in t (sec) E V x I x t
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Converting Hours to Seconds
1 hour has 60 minutes 1 minute has 60
seconds 60 x 60 3600 seconds in one hour So 1
hour has 3600 seconds (1 x 3600). 2 hours would
have 7200 sec (2 x 3600).
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Try This
Calculate the energy released from a battery in a
flashlight bulb that was switched on for 4.5
hours, in which the voltage drop was 6V and the
current flowing through the bulb was
0.35A. Whats the important information? Energy
(E) ? joules (J) Voltage 6V Current
0.35A Time 4.5 hours - Change to seconds
4.5 hours x 3600 seconds/hour 16 200
seconds
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Calculate the energy released from a battery in a
flashlight bulb that was switched on for 4.5
hours, in which the voltage drop was 6V and the
current flowing through the bulb was 0.35A.
E V x I x t E 6V x 0.35A x 16
200sec E 34 020 joules The energy released
from the battery was 34 020 joules.
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The Same Question Finding the Answer in Watt
Hours
Calculate the energy released from a battery in a
flashlight bulb that was switched on for 4.5
hours, in which the voltage drop was 6V and the
current flowing through the bulb was 0.35A. 34
200 Joules is a large number. To make it more
practical we can find the answer in Watt Hours
(Wh) E 6V x 0.35A x 4.5h E 9.45 Wh
E V x I x t