Transcript Electricity Energy   Is the ability to do work Comes in 2 main types (but many forms) • Potential energy is stored energy like •  gravity, chemical,

Electricity
Energy
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
Is the ability to do work
Comes in 2 main types (but many
forms)
• Potential energy is stored energy like
•

gravity, chemical, nuclear and electrical
Kinetic energy is the energy of moving
objects like light, sound and mechanical
Energy can be converted from
one form to another
Electrical Energy
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A battery holds Electrical Potential Energy
(Potential, because it is stored energy)
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Voltage is a measure of the difference in
electrical energy between 2 places in a circuit
A 12 volt battery has 12 volts of potential
energy difference between the positive
terminal and the negative terminal
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A voltmeter measure the “potential
difference” between 2 points in a circuit
each volt equals 1 joule of energy per
charge
Voltage (symbol V) units are the volt (V)
Electric Current
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is the measure of how many charges are
passing a point in a circuit every second
Symbol is I
Unit is the Amp (A)
Is measured using an ammeter
Resistance
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Is a measure of how hard it is for charges to
pass through an object
Higher resistance means more energy is
needed to pass through
Resistance, voltage and current are all related
•
If the voltage is kept the same, but the resistance is
increased, the current decreases
Resistance (R) is measured in ohms (symbol
Ω)
Name
Voltage
Current
Resistance
Symbol
V
I
R
Unit
(Symbol)
Volts (V)
Amps (A)
Ohms (Ω)
Assignment
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
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Pg 275 reading check 1,2,3,4,5,6,9
Pg 279 Checking Concepts 1,2,3,5,6
Pg 279 Understanding Key Ideas 1,2
Ohm’s Law
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“the current through an object is equal to
the voltage across the object divided by
the resistance”
I = V/R
If V =6 V and R = 2 Ω then
The current (I) = 6/2 = 3 Amps
Ohms Law
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Use the triangle to
help solve ohms law
problems
V= I x R
I = V /R
R = V/I
V
I
R
Ohms Law Problems
1.
A 1.5 volt battery is connected to a light
bulb and produces 0.5 amps of current.
What is the RESISTANCE of the bulb
V = 1.5 V, I = 0.5 A
R = V/I = 1.5/0.5 = 3.0 ohms (Ω)
2.
A different battery is put in the circuit
above and the current changes to 1.5A.
What is the voltage of the new battery?
I=1.5 A, R = 3.0 Ω
V = I x R = 1.5 x 3.0 = 4.5 V
Now you try a couple:
1.
A 6 Volt battery creates a current of 0.6 amps
when connected to a motor. What is the
resistance of the motor?
V = 6.0 V, I = 0.6 A
R = V/I, R = 6.0/0.6 = 10 Ω
2.
A 4.5 Volt IPod has a resistance of 900 ohms.
What is the current when the ipod is turned
on?
V = 4.5 V, R = 900 Ω
I = V/R = 4.5/900 = 0.005 A (5 mA)
Ohms Law Problems
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Handout
Text book “Practice Problems” page 293
and page 294
Pg 301 #1-5, 8-10,12,13
Circuit types

Series circuits
• Have one pathway for electricity to flow
• Current decreases as more loads (resistors)
are added (if voltage is kept the same)

Parallel circuits
• Have more than one path for electricity to flow
• Current increases as more loads are added
Series Circuit
Parallel Circuit
Circuit Analysis
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The voltage drop over each load sums to the
voltage across the battery
The current through each path sums to the
current supplied by the battery
In a series circuit, the voltage drop across each
device can differ, but the current through each
device is the same
In a parallel circuit, the voltage drop across
each device is the same, but the current
through each device can differ.
A Parallel Circuit
Still needed:
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Static Electricity
Insulators and conductors
Total resistance in a series circuit
How the current and voltage change as
more loads are added to
• A series circuit
• A parallel circuit