Introduction to Electricity

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Introduction to Electricity
Chapter 17
Preview
Section 1 Electric Charge and Static
Electricity Section 2 Electric Current and
Electrical Energy Section 3 Electrical
Calculations Section 4 Electric Circuits
Concept Mapping
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Section 1 Electric Charge and Static Electricity
Chapter 17
Bellringer
Write a definition for electric charge in your
own words in your science journal. When do you
experience electric charges most, in winter or in
summer? Explain your reasoning.
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Section 1 Electric Charge and Static Electricity
Chapter 17
Objectives

• Describe how charged objects interact by using
  the law of electric charges.
• Describe three ways in which an object can
  become charged.
• Compare conductors with insulators.
• Give two examples of static electricity and
  electric discharge.

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Section 1 Electric Charge and Static Electricity
Chapter 17
Electric Charge

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

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Section 1 Electric Charge and Static Electricity
Chapter 17
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Section 1 Electric Charge and Static Electricity
Chapter 17
Electric Charge, continued

• The Force Between Protons and Electrons Because
  protons and electrons have opposite charges, they
  are attracted to each other.
• The Electric Force and the Electric Field The
  force between charged objects is an electric
  force. An electric field is the region around a
  charged object in which an electric force is
  exerted on another charged object.

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Section 1 Electric Charge and Static Electricity
Chapter 17
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Section 1 Electric Charge and Static Electricity
Chapter 17
Charge It!

• Friction Charging by friction happens when
  electrons are wiped from one object onto
  another.
• Conduction Charging by conduction happens when
  electrons move from one object to another by
  direct contact.
• Induction Charging by induction happens when
  charges in an uncharged metal object are
  rearranged without direct contact with a charged
  object.

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Section 1 Electric Charge and Static Electricity
Chapter 17
Charge It!, continued
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Section 1 Electric Charge and Static Electricity
Chapter 17
Charge It!, continued

• 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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Section 1 Electric Charge and Static Electricity
Chapter 17
Charging by Contact
Click below to watch the Visual Concept.
Visual Concept
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Section 1 Electric Charge and Static Electricity
Chapter 17
Moving Charges

• Conductors An electrical conductor is a
  material in which charges can move easily.
• Insulators An electrical insulator is a
  material in which charges cannot move easily.

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Section 1 Electric Charge and Static Electricity
Chapter 17
Static Electricity

• Static electricity is the electric charge at
  rest on an object.
• Electric Discharge The loss of static
  electricity as charges move off an object is
  called electric discharge. One of the most
  dramatic examples of electric discharge is
  lightning. The next slide shows how lightning is
  formed.

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Section 1 Electric Charge and Static Electricity
Chapter 17
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Section 1 Electric Charge and Static Electricity
Chapter 17
Static Electricity, continued

• Lightning Dangers It is particularly dangerous
  to be at the beach or on a golf course during a
  lightning storm. Even standing under a tree
  during a storm is dangerous.
• Lightning Rods A lightning rod is a pointed rod
  connected to the ground by a wire. Objects that
  are joined to Earth by a conductor, such as a
  wire, are grounded.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Bellringer
What is the difference between something that is
direct and something that is alternating? How
does the difference relate to electric current?
Record your responses in your science journal.
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Section 2 Electric Current and Electrical Energy
Chapter 17
Objectives

• Describe electric current.
• Describe voltage and its relationship to
  electric current.
• Describe resistance and its relationship to
  electric current.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Objectives, continued

• Explain how a cell generates electrical energy.
• Describe how thermocouples and photocells
  generate electrical energy.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Electric Current

• Electric current is the rate at which charges
  pass through a given point. Electric current is
  expressed in units called amperes, or amps.
• Making Charges Move When you flip a switch, an
  electric field is set up in the wire at the speed
  of light. The electric field causes the free
  electrons in the wire to move.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Electric Current, continued

• Commanding Electrons to Move This electric
  field is created so quickly that all electrons
  start moving through the wire at the same
  instant. Think of the electric field as a command
  to the electrons to charge ahead.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Electric Current, continued

• AC and DC There are two kinds of electric
  currentdirect current (DC) and alternating
  current (AC).

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Section 2 Electric Current and Electrical Energy
Chapter 17
Voltage

• Voltage is the potential difference between two
  points in a circuit. Voltage is expressed in
  volts (V).
• Voltage and Energy Voltage is a measure of how
  much work is needed to move a charge between two
  points.You can think of voltage as the amount of
  energy released as a charge moves between two
  points in the path of a current.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Voltage, continued

• Voltage and Electric Current As long as there
  is a voltage between two points on a wire,
  charges will flow in the wire. The size of the
  current depends on the voltage.
• Varying Nature of Voltage Different devices
  need different levels of voltage.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Resistance

• Resistance is the opposition to the flow of
  electric charge.
• Resistance and Material Good conductors, such
  as copper, have low resistance. Poor conductors,
  such as iron, have higher resistance.
• Resistance, Thickness, and Length Thick, short
  wires have less resistance than thin, long wires.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Resistance, continued

• Resistance and Temperature In general, the
  resistance of metals increases as temperature
  rises.

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Section 2 Electric Current and Electrical Energy
Chapter 17
Factors That Affect Resistance
Click below to watch the Visual Concept.
Visual Concept
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Section 2 Electric Current and Electrical Energy
Chapter 17
Generating Electrical Energy

• 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.
• Kinds of Cells Two kinds of cells are wet cells
  and dry cells. The electrolytes in dry cells are
  solid or pastelike.

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Section 2 Electric Current and Electrical Energy
Chapter 17
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Section 2 Electric Current and Electrical Energy
Chapter 17
Generating Electrical Energy, continued

• Thermocouples Thermal energy can be converted
  into electrical energy by a thermocouple.
• Photocells A photocell converts light energy
  into electrical energy.

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Section 3 Electrical Calculations
Chapter 17
Bellringer
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. Record your answers
in your science journal.
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Section 3 Electrical Calculations
Chapter 17
Objectives

• Use Ohms law to calculate voltage, current, and
  resistance.
• Calculate electric power.
• Determine the electrical energy used by a
  device.
• Compare the power ratings of different
  electrical appliances.

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Section 3 Electrical Calculations
Chapter 17
Connecting Current, Voltage, and Resistance

• Georg Ohm (1789 1854) studied the resistances
  of materials. He measured the current that
  resulted from different voltages applied to a
  piece of metal wire.
• Ohms Law Ohm found that the ratio of voltage
  to current is a constant for each material. This
  ratio is the resistance of the material.

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Section 3 Electrical Calculations
Chapter 17
Connecting Current, Voltage, and Resistance,
continued

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Section 3 Electrical Calculations
Chapter 17

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Section 3 Electrical Calculations
Chapter 17
Electric Power

• What Is Electric Power? The rate at which
  electrical energy is changed into other forms of
  energy is electric power. Electric power is
  calculated using the following equation

power ? voltage ? current, or P ? V ? I

• Watt The Unit of Power The unit for power is
  the watt (W). Another common unit of power is the
  kilowatt (kW). One kilowatt is equal to 1,000 W.

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Section 3 Electrical Calculations
Chapter 17
Electric Power, continued

• Power Ratings When you read the wattage label
  on a light bulb, you are reading the bulbs power
  rating. The power rating describes the rate at
  which an electric device uses electrical energy.

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Section 3 Electrical Calculations
Chapter 17
Measuring Electrical Energy

• The amount of electrical energy used in a home
  depends the power of the electrical devices in
  the house and the length of the time that those
  devices are on. The equation for electrical
  energy is as follows

electrical energy ? power ? time, or E ? P ? t
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Section 3 Electrical Calculations
Chapter 17

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Section 3 Electrical Calculations
Chapter 17
Measuring Electrical Energy, continued

• 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.
• How to Save Energy Every appliance uses energy.
  Replacing items that have high power ratings with
  items that have lower ratings is a way to save
  energy.

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Section 3 Electrical Calculations
Chapter 17
Measuring Electrical Energy, continued

• Its All About the Bulb All of the lighting in
  a home could make up as much as 25 of a homes
  energy consumption. So, buying and using
  energyefficient light bulbs can make a big
  difference in the amount of energy used by a
  household.
• EnergySaving Programs Many governments and
  organizations around the world have started
  programs to help save energy and natural
  resources.

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Section 4 Electric Circuits
Chapter 17
Bellringer
What happens when you turn the lights on? What
allows lights to be turned on and off? Write your
answer or draw an explanatory picture for later
reference in your science journal. What happens
beyond the confines of the room when you flip the
light switch?
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Section 4 Electric Circuits
Chapter 17
Objectives

• Name the three essential parts of a circuit.
• Compare series circuits with parallel circuits.
• Explain how fuses and circuit breakers protect
  your home against short circuits and circuit
  overloads.

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Section 4 Electric Circuits
Chapter 17
Parts of an Electric Circuit

• Forming a Loop An electric circuit is a
  complete, closed path through which electric
  charges flow.
• All circuits need three basic parts an energy
  source, wires, and a load.

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Section 4 Electric Circuits
Chapter 17
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Section 4 Electric Circuits
Chapter 17
Parts of an Electric Circuit, continued

• A Switch to Control a Circuit Sometimes, a
  circuit also contains a switch. A switch is used
  to open and close a circuit.

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Section 4 Electric Circuits
Chapter 17
Types of Circuits

• Series Circuits A series circuit is a circuit
  in which all parts are connected in a single
  loop.
• Uses for Series Circuits 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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Section 4 Electric Circuits
Chapter 17
Types of Circuits, continued

• Parallel Circuits A parallel circuit is a
  circuit in which loads are connected side by
  side.
• Uses for Parallel Circuits Almost all
  appliances are built with parallel circuits so
  that they will keep working if part of the system
  fails.

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Section 4 Electric Circuits
Chapter 17
Household Circuit Safety

• Circuit Failure Broken wires or water can cause
  a short circuit. In a short circuit, charges do
  not go through one or more loads in the circuit.
• Fuses A fuse has a thin strip of metal. Fuses
  keep charges from flowing if the current is too
  high.

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Section 4 Electric Circuits
Chapter 17
Household Circuit Safety, continued

• Circuit Breakers A circuit breaker is a switch
  that automatically opens if the current is too
  high. Charges stop flowing.
• Electrical Safety Tips Do not overload circuits
  by plugging in too many electrical devices. Do
  not use electrical devices near water.

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Introduction to Electricity
Chapter 17
Concept Mapping
Use the terms below to complete the Concept
Mapping on the next slide.
battery electrical energy thermocouple
light energy thermal energy light energy thermal energy
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Introduction to Electricity
Chapter 17
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Introduction to Electricity
Chapter 17