ELECTRICITY

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ELECTRICITY
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Goals
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Explain the flow of electrons in terms of
alternating and direct current. the
relationship among voltage, resistance and
current. simple series and parallel circuits.
Explain static electricity in terms of
friction induction conduction
Construct simple circuits
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Properties of Electric Charge
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• Atomic Structure Composed of three main
  particles
• Proton
• Neutron
• Electron

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Things to Remember
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• Everything is made of atoms.
• Electrons can move from one atom to another atom.

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Static Electricity
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• The temporary building up of charge on an object.
• Some atoms hold e- more tightly than others.
• Ex. Your shoes
• and Carpet

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If you walk across a carpet, electrons move from
the rug to you (because of friction). Now you
have extra electrons. Touch a door knob and ZAP!
The electrons move from you to the knob. You get
a shock.
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• Static electricity is actually an imbalance in
  the amounts of positive and negative charges in
  the surface of an object.

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Three ways to induce a charge in an object
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• Friction
• Induction
• Conduction (Contact)

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Charging by Induction
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• Involves the charging of one object by another
  without direct contact.

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Charging by Conduction
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• involves the direct contact of a charged object
  to a neutral object.

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Detecting an Electric Charge
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Electroscope helps detect electric charge
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• Electrostatics Lab

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Electric Current
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• The constant flow of electrons.

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Transfer of Electric Charge
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Clip

• Some materials do not allow electric charge to
  move freely Insulators
• Ex glass, rubber

Has to do with the molecular structure of the
material

• Some materials allow electric charge to move
  freely Conductors
• Ex copper, aluminum

• Semiconductors
• In their natural state they are insulators
  Material can be added to the material to increase
  its conductivity
• Ex Silicon and Germanium

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Voltage
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• For electrons to flow there must be a potential
  difference between to places.

• This is called voltage, which is the Push that
  causes electrons to flow.
• Its electrical Pressure.
• Charges flow from high voltage to low voltage.
• Measured in Volts (V).

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Current
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• The measure of how many electrons per second are
  flowing through the wire is the amperage (A).

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Electrical current
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• The of e- is called current (unit Ampere or
  Amp. )
• Electrical current is like the amount or volume
  of water flowing through the hose.

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Resistance
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• The tendency for a material to oppose the flow of
  electrons.
• Different material have different amounts of
  resistance to the flow of electrons.
• The unit of resistance is ohm.

 
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Resistance
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• Ex gold, silver, and copper have low resistance,
  which means that current can flow easily through
  these materials.
• Glass, plastics, and wood have very high
  resistance, which means that current cannot pass
  through these materials easily.

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Resistance in Wires

• Thick wire Vs. Thin Wire

Thin wires provide more resistance than do thick
wires
Resistance also depends on temperature, usually
increasing as the temperature increases
resistance
Resistance in wires produces a loss of energy
(usually in the form of heat), so materials with
no resistance produce no energy loss when
currents pass through them.
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Electric Circuits
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• A pathway for electrons to flow.
• Electrons follow the path of least resistance.

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Open Circuits
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Electrons follow the path of least resistance
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Closed Circuits
Electrons follow the path of least resistance
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Series Circuit
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• The current has only one path to follow.

Electrons follow the path of least resistance
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Parallel Circuits
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Two or more branches for the
current to flow.
Electrons follow the path of least resistance
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Lab Goals
Investigate the properties of electricity and
magnetism. b) Understand the relationship among
voltage, resistance current. c) Understand
how to build simple series and parallel circuits.
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From Lab
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• In a series circuit
• the current through each of the components is the
  same, and the total voltage in the circuit is the
  sum of the voltages across each component.
• In a parallel circuit..
• the voltage across each of the components is the
  same, and the total current is the sum of the
  currents through each component.

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OHM'S LAW
In a material, the current (I) is directly
proportional to the voltage (V) and inversely
proportional to the resistance (R).
V
VIR
I
OR
R
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• a. What is the total voltage across the bulbs?
• b. What is the total resistance of the circuit?
• c. What is the current in the circuit?
• d. What is the voltage drop across each light
  bulb?

6V
3?
2V
2A
e. What happens to the brightness of each bulb in
a series circuit as additional bulbs are added?
Why?
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• a. What is the voltage across each resistor?
• b. What is the current in each branch?
• c. What is the total current provided by the
  battery?

• The voltage is equal across all components in a
  parallel circuit. (Therefore, the voltage across
  R1 is equal to the voltage across R2 which is
  equal to the voltage across the battery.)
• The total current in the circuit is equal the sum
  of all individual branch currents.

12V
6 A and 4 A
10 A
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• Four identical light bulbs are connected in a
  circuit as shown below. The current is greatest
  through which of the light bulbs?
• A 1
• B 2
• C 3
• D 4

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How do batteries work? Batteries have three
parts, an anode (-), a cathode (), and the
electrolyte. The cathode and anode (the positive
and negative sides at either end of a traditional
battery) are hooked up to an electrical circuit.
                                 
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Dry Cell
The chemical reactions in the battery causes a
build up of electrons at the anode. This results
in an electrical difference between the anode and
the cathode. You can think of this difference as
an unstable build-up of the electrons. The
electrons wants to rearrange themselves to get
rid of this difference. But they do this in a
certain way. Electrons repel each other and try
to go to a place with fewer electrons.
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Wet Cell  -uses liquids for the electrolytes, as
opposed to the dry cell               
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Electric Power
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• The rate at which electrical energy is
  transferred by an electric circuit.
• The SI unit of power is the watt
• Joule's Law

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What is a kilowatt hour?
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• How long you run an appliance.
• How much energy is used?
• Energy used Power (kW) x Time (hrs)
• E P x t
• To find cost
• Ex 10 per kilowatt hour
• E x

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• 105 V are used to power an appliance that needs
  15.0 amps. What is the power used?
• 1575 W 1.575kW
• How much energy is used when this appliance is
  used for 30.0 days- 24hrs a day?
• 1134 kW -hr
• If the power company charges 8/Kw-h, what is the
  cost of the energy above.
• 90.72
• An electric refrigerator rated 400 W operates 8
  hour/day. What is the cost of energy to operate
  it for 30 days at 8/Kw-h?

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How a Lightbulb Works
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Review Series and Parallel Circuits clip