electricity part 2. learning objectives tlw know the impact of energy transfer and energy conversion...
TRANSCRIPT
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Electricity
Part 2
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Learning Objectives
• TLW know the impact of energy transfer and energy conversion in everyday life (TEKS 5)
• TLW evaluate, investigate and compare series and parallel circuits (TEKS 5.F)
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Flow of Electricity• An electric charge has potential
energy• This potential energy is called
electrical potential energy• Electrical potential energy depends
on the position of the electric field• Remember – all charged objects
have an electric field
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• Electrical potential energy = potential energy of a charged object due to its position in an electric field
• The electrical potential energy between two objects increases the closer they get
• The electrical potential energy decreases as the distance between two objects increase
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Potential Difference• Potential difference is the change in
electrical potential energy of a charged particle
• The change occurs when a charge moves from one place to another in an electric field
• The SI unit for potential difference is volt symbol is (v)
• 1 volt (V) = 1 joule per coulomb
• Usually referred to as voltage
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Batteries• A battery can convert chemical energy
into electrical energy• Batteries are sources of electrical
current because of the potential difference between the terminals
• One terminal is positive and one is negative
• This allows for an electrical current or the movement of charged particles
• Batteries range from 1.5V to 12V (car battery)
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Positive Terminal
Negative Terminal
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Flow of electrons• A voltage sets charges in motion• This creates a current = the rate at which
electric charges move• The SI unit for currents is ampere or amps –
symbol of i• Batteries are a direct current source
–Because the charges always move in the same direction (negative to positive)
• When the current is the movement of positive charges it is called conventional current
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Resistance• Most electrical appliances in the US are designed for
the same voltage = 110 V– You have to use a converter if you travel to Europe
as they commonly use 220 V for appliances• But light bulbs come in different varieties
– So some are very bright and some are dim• Because they have different amounts of currents in
them (remember a current is the rate at which charges move)
• They have different currents because of their resistance
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How Resistance works
• Resistance is caused by internal friction
• Friction slows the movement of charges down
• The filament in a light bulb is the resistance
–A 40 W light bulb has a higher resistance than a 100 W light bulb
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More on Resistance
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Review Vocab• Voltage – amount of potential energy that each
unit of electrical charge has (measured in volts - V)
• Current – rate of flow of electric charges (measured in amps - I)
• Resistance – measure of an objects ability to conduct electricity (measured in ohms – Ω - R)
• Power – measure of work done by electrical current (measured in watts – W)
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Calculations• Resistance = voltage/current
R=V/I– The SI unit for resistance is ohm (Ω)
• Current = voltage/resistance
I=V/R– The SI Unit for current is amps (A)
• Voltage = current x resistance
V = I x R– The SI Unit for voltage is volts (v)
• Power = voltage x current
P = I x V– The SI Unit for power is watts (w)
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Ohm’s Law• Ohm’s Law is a relationship between
voltage, current, and resistance
R
VI
Current (amps)
Voltage (volts, V)
Resistance (ohms, )More on Ohm’s Law
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R
VI
V
I R
Magic Triangle for Electricity
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Example 1A 1.5 volt battery is used in a flashlight that has a
light bulb with a 10 ohm resistor. How much current will flow through the light?
I = V .
R
I = 1.5 v
10 Ω
I = 0.15 A
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Example 2A light bulb has 1 amp of current flowing through it
when a direct current of 10 volts is applied. What is the filament’s resistance?
R = V .
I
R = 10 v
1 A
R = 10 Ω
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Example 3How much voltage does a battery have that
produces a current of 3 amps through a 3 ohm resistor?
V = I x R
V = 3 A x 3 Ω
V = 9 v
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The Danger of Electric Shock
A CD player uses 2.5A
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Electric Circuits
• Electric Circuits – a device that provides a complete pathway for the movement of charges
• A closed circuit = a complete path, creating current to flow
• An open circuit = no charge can flow, no current created
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Parts to a circuit• Switch = allows the circuit to be open or closed;
“on or off”• Direct current source = creates the potential
difference; Ex. battery• Resistors = controls the current; how much is
flowing• Wire or conductors = connects the circuit
together• Electrical “object” = the reason for having the
circuit (the stuff you want to use/operate)
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Schematic diagram• To draw a circuit a schematic
diagram is used
• Specific symbols represent each part of the circuit
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Schematic Symbols• Direct Current source
• Switch
• Resistor
• Wire or conductor
• Bulb or lamp
Open
Closed
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Series Circuit• A circuit that has only one path
for the electrons to take is called a series circuit
• If one object along the path is removed – the circuit will not work
• In a series circuit – the circuit either works or doesn’t
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Parallel Circuits
• A circuit that allows electrons to flow through different pathways is called a parallel circuit
• If an object along the path is removed, the electrons can still flow through the circuit
• Most homes are wired on a parallel circuit
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Fuses and Breakers• When too many things are “plugged
in” at one time, the circuit is overloaded
• This can lead to fires
• When worn out electrical cords are used – two wires may touch
–This creates another pathway for electrons to flow
–This is called short circuit
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• Fuses are used to prevent circuit overload
• A fuse is a metal strip that melts when a current becomes too great
• ALWAYS find out why a fuse “blows out” before you replace it
• A circuit breaker acts as a switch
–A breaker is designed to open the circuit to prevent any more current from flowing
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Independent Practice
• Calculations to determine voltage, current, and resistance
• Calculations to determine cost of electrical usage
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Lab
• In Periodic Groups, read entire procedure for understanding– Lab to be assigned by teacher
• Set up experiment using scientific method
• Identify potential hazards, precautions to take, and any PPE needed