Electricity

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Electricity

• Chapter 17

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Electric Charge

• Charges Exert Force
• Atoms are composed of particles with charges.
  The law of electric charges states that like
  charges repel and opposite charges attract.

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The Force Between Protons and Electrons

• Protons and electrons have opposite charges, they
  are attracted to each other

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The Electric Force and the Electric Field

• Electric force- the force of attraction or
  repulsion on a charged particle that is due to an
  electric field
•  
• Electric field the space around a charged
  object in which another charged object
  experiences an electric force

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Charge it!

• Friction

• Conduction

• Friction- occurs when electrons are wiped
• from one object to another
•  
•  

• Conduction electrons move from one object to
  another by direct contact.
•  

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Charge it!

• Induction charges in an uncharged metal object
  are rearranged without direct contact with a
  charged object

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Conservation of Charge

• When you charge something by any method, no
  charges are created or destroyed. The numbers of
  electrons and protons stay the same.
• Detecting Charge
• You can use a device called an electroscope to
  see if something is charged

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Moving Charges

• Conductors- a material in which charges can move
  easily
• Examples copper, aluminum
• Insulators- a material in which charges
• cannot move freely
• Examples plastic, rubber, wood

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Static Electricity

• Static electricity- electric charge at rest
  produced from friction or induction
• Electric Discharge the release of electricity
  stored in a source

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17.2 Electric Current Energy

• Electric Current (I) rate at which charges pass
  a given point
• When you flip a switch, an electric field is set
  up in the wire at the speed of light. The
  electric field causes the electrons in the wire
  to move.
• This electric field is created so quickly that
  all electrons start moving through the wire
  instantly.
• Think of the electric field as a command to the
  electrons to charge ahead.

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Types Electric current

• Direct Current (DC)

• Alternating Current (Ac)

• Direct Current (DC) charges always flow in one
  direction.
• Ex batteries used in appliances

• Alternating Current (AC) charges shift
• from flowing in one direction to
  flowing in
• the reverse direction
• EX Wiring in house

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Voltage and Energy

• Voltage the potential difference between points
• SI unit Volts (V)
•  
• You can think of voltage as the amount of energy
  released as a charge moves between two points in
  the path of a current.
• As long as there is a voltage between 2 points,
  charges will flow in the wire. The size of the
  current depends on the voltage.

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Varying Nature of Voltage

• Different devices need different levels of
  voltage.
• 1.5 V 9 V
  12 V

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Resistance

• Resistance (R) opposition to the flow of
  electric charge
• SI unit ohms (?)
• Good conductors, such as copper, have low
  resistance
• Poor conductors, such as iron, have high
  resistance
• Resistance depends on thickness, length,
  temperature
• Thick, short wires have less resistance than
  long, thin wires.
• The resistance of metals increases as temperature
  increases

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Resistance

• Resistance (R) opposition to the flow of
  electric charge
• SI unit ohms (?)
• Good conductors, such as copper, have low
  resistance
• Poor conductors, such as iron, have high
  resistance
• Resistance depends on thickness, length,
  temperature
• Thick, short wires have less resistance than
  long, thin wires.
• The resistance of metals increases as temperature
  increases

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Resistance
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Generating Electrical Energy

• Remember energy is not created or destroyed it
  only changes forms
• Parts of a Cell
• A cell contains a mixture of chemicals called an
  electrolyte. Every cell also has a pair of
  electrodes made from conducting materials

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Types of Cells

• There are 2 types of cells
• Wet have an electrolyte
• Example batteries sulfuric acid is the
  electrolyte
• Dry have a dry electrolyte
• Example small radios or flashlights

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Generating Electrical Energy

• Cells change chemical or radiant energy into
  electrical energy. Batteries are made of one or
  more cells.
• Thermocouple can take thermal energy and transfer
  it to electrical energy.
• Photocell convert light energy into electrical
  energy.

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17.3 Electrical Calculations

• How fast is a nanosecond? A nanosecond (ns) is
  one-billionth of a second. Electrical signals
  travel at 30 cm/ns. Calculate how far electrical
  signals travel in 1 second.
•  

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Connecting Current, Voltage, and Resistance

• Georg Ohm Ohm (1789 1854) studied the resistance
  of materials. He measured the current that
  resulted from different voltages applied to a
  piece of metal wire.
• Ohms Law the ratio or voltage (V) to current
  (I) is the resistance (R) of a material
• V I x R

Electric Power
Unit SI Unit
Voltage (V) V - volt
Current (I) A- Amps
Resistance (R) Ohm - ?
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Ohms Law Calculations

• Ex 1 What is the voltage if the current is 2 A
  and the resistance is 12 ? ?
• Ex 2 Find the voltage if the current is 0.2 A
  and the resistance is 2 ?

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Ohms Law Calculations

• Ex 3 The resistance of an object is 4 ?. If the
  current in the object is 9 A, what is the voltage
  used?
• Ex 4 An object has a resistance of 20 ?.
  Calculate the voltage needed to produce a current
  of 0.5 A.

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Electric Power

• Electrical Power (P) the rate at which
  electrical energy is converted into other forms
  of energy
• Si Unit Watts (W)
• Power voltage x current
• P V x I

Unit SI Unit
Voltage (V) V - volt
Current (I) A- Amps
Power (P) W - Watts
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Electrical Power Calculations

• Ex 1 A toaster draws approximately 10 A of
  current. A home receives 120 V at each electrical
  outlet. What is the power of the toaster?
• Ex 2 A car uses a 12 V battery. One headlight
  draws 3.0 A. What is the power of the headlight?

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Electrical Power Calculations

• EX 3 A light bulb draws a 0.5 A current at a
  voltage of 120 V. What is the power rating of the
  light bulb?

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Electrical Energy

• Measuring Household Energy Use
• Different amounts of electrical energy are used
  each day in a home. Electric companies usually
  calculate electrical energy by multiplying the
  power in kilowatts by the time in hours.

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17.4 Electric Circuit

• Just like a roller coaster, an electric circuit
  always forms a loop it starts and ends at the
  same place
• Parts of an Electric Circuit
• Energy source (Battery)
• Wires
• Load (light bulb, appliance)

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Switches

• Sometimes, a circuit also contains a switch
• Switch opens or closes a circuit
• Closed electrons can flow
• Open electrons cannot flow

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Types of Circuits

• Series Circuit a circuit in which the parts are
  joined one after another such that the current in
  each part is the same.
• One path for charges to follow charges must
  flow through each part of the circuit
• The voltage across each load is different

Series circuits are useful in wiring burglar
alarms. If any part of the circuit fails, there
will be no current in the system and the alarm
will sound.
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Types of circuits

• Parallel Circuits - a circuit in which the parts
  are joined in branches so that the voltage
  (potential difference) across each part is the
  same
• Loads do not have the same current
• Charges have more than one path to follow

Parallel Circuits are used in almost all
appliances and decorative string lights
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Household circuit safety

• Circuits can fail if they are overloaded or a
  wire breaks or has water damage.
• To prevent fire
• Fuses
• A thin strip of metal in circuit that the charges
  flow through.
• If the current is too high, the metal will
  melt and the circuit
• is broken
• Circuit Breakers
• A switch that automatically opens if the current
  is too high. A metal strip heats up, bends, and
  opens the switch stopping the flow of current