Introduction to Electricity

1. 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

2. Section1 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.

3. Section1 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.

4. Section1 Electric Charge and Static Electricity Chapter 17 Electric Charge • Charges Exert ForceAtoms are composed of particles with electric charge. The law of electric charges states that like charges repel and opposite charges attract.

5. Section1 Electric Charge and Static Electricity Chapter 17

6. Section1 Electric Charge and Static Electricity Chapter 17 Electric Charge, continued • The Force Between Protons and ElectronsBecause protons and electrons have opposite charges, they are attracted to each other. • The Electric Force and the Electric FieldThe 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.

7. Section1 Electric Charge and Static Electricity Chapter 17

8. Section1 Electric Charge and Static Electricity Chapter 17 Charge It! • FrictionCharging by friction happens when electrons are “wiped” from one object onto another. • ConductionCharging by conduction happens when electrons move from one object to another by direct contact. • InductionCharging by induction happens when charges in an uncharged metal object are rearranged without direct contact with a charged object.

9. Section1 Electric Charge and Static Electricity Chapter 17 Charge It!, continued

10. Section1 Electric Charge and Static Electricity Chapter 17 Charge It!, continued • Conservation of ChargeWhen you charge something by any method, no charges are created or destroyed. The numbers of electrons and protons stay the same. • Detecting ChargeYou can use a device called an electroscope to see if something is charged.

11. Section1 Electric Charge and Static Electricity Chapter 17 Charging by Contact Click below to watch the Visual Concept. Visual Concept

12. Section1 Electric Charge and Static Electricity Chapter 17 Moving Charges • ConductorsAn electrical conductor is a material in which charges can move easily. • InsulatorsAn electrical insulator is a material in which charges cannot move easily.

13. Section1 Electric Charge and Static Electricity Chapter 17 Static Electricity • Static electricityis the electric charge at rest on an object. • Electric DischargeThe 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.

14. Section1 Electric Charge and Static Electricity Chapter 17

15. Section1 Electric Charge and Static Electricity Chapter 17 Static Electricity, continued • Lightning DangersIt 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 RodsA 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.

16. Section2 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.

17. Section2 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.

18. Section2 Electric Current and Electrical Energy Chapter 17 Objectives, continued • Explain how a cell generates electrical energy. • Describe how thermocouples and photocells generate electrical energy.

19. Section2 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.

20. Section2 Electric Current and Electrical Energy Chapter 17 Electric Current, continued • Commanding Electrons to MoveThis 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.

21. Section2 Electric Current and Electrical Energy Chapter 17 Electric Current, continued • AC and DCThere are two kinds of electric current—direct current (DC) and alternating current (AC).

22. Section2 Electric Current and Electrical Energy Chapter 17 Voltage • Voltageis the potential difference between two points in a circuit. Voltage is expressed in volts (V). • Voltage and EnergyVoltage 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.

23. Section2 Electric Current and Electrical Energy Chapter 17 Voltage, continued • Voltage and Electric CurrentAs 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 VoltageDifferent devices need different levels of voltage.

24. Section2 Electric Current and Electrical Energy Chapter 17 Resistance • Resistance is the opposition to the flow of electric charge. • Resistance and MaterialGood conductors, such as copper, have low resistance. Poor conductors, such as iron, have higher resistance. • Resistance, Thickness, and LengthThick, short wires have less resistance than thin, long wires.

25. Section2 Electric Current and Electrical Energy Chapter 17 Resistance, continued • Resistance and TemperatureIn general, the resistance of metals increases as temperature rises.

26. Section2 Electric Current and Electrical Energy Chapter 17 Factors That Affect Resistance Click below to watch the Visual Concept. Visual Concept

27. Section2 Electric Current and Electrical Energy Chapter 17 Generating Electrical Energy • Parts of a CellA cell contains a mixture of chemicals called an electrolyte. Every cell also has a pair of electrodes made from conducting materials. • Kinds of CellsTwo kinds of cells are wet cells and dry cells. The electrolytes in dry cells are solid or pastelike.

28. Section2 Electric Current and Electrical Energy Chapter 17

29. Section2 Electric Current and Electrical Energy Chapter 17 Generating Electrical Energy, continued • ThermocouplesThermal energy can be converted into electrical energy by a thermocouple. • PhotocellsA photocell converts light energy into electrical energy.

30. Chapter 17 Section3 Electrical Calculations 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.

31. Chapter 17 Section3 Electrical Calculations Objectives • UseOhm’s law to calculate voltage, current, and resistance. • Calculateelectric power. • Determinethe electrical energy used by a device. • Compare the power ratings of different electrical appliances.

32. V R , or V I R = =  I Chapter 17 Section3 Electrical Calculations 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. • Ohm’s LawOhm found that the ratio of voltage to current is a constant for each material. This ratio is the resistance of the material. †

33. Chapter 17 Section3 Electrical Calculations Connecting Current, Voltage, and Resistance, continued †

34. Chapter 17 Section3 Electrical Calculations †

35. Chapter 17 Section3 Electrical Calculations 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 PowerThe unit for power is the watt (W). Another common unit of power is the kilowatt (kW). One kilowatt is equal to 1,000 W.

36. Chapter 17 Section3 Electrical Calculations Electric Power, continued • Power Ratings When you read the wattage label on a light bulb, you are reading the bulb’s power rating. The power rating describes the rate at which an electric device uses electrical energy.

37. Chapter 17 Section3 Electrical Calculations 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

38. Chapter 17 Section3 Electrical Calculations †

39. Chapter 17 Section3 Electrical Calculations 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 EnergyEvery appliance uses energy. Replacing items that have high power ratings with items that have lower ratings is a way to save energy.

40. Chapter 17 Section3 Electrical Calculations Measuring Electrical Energy, continued • It’s All About the Bulb All of the lighting in a home could make up as much as 25% of a home’s energy consumption. So, buying and using energy–efficient light bulbs can make a big difference in the amount of energy used by a household. • Energy–Saving Programs Many governments and organizations around the world have started programs to help save energy and natural resources.

41. Section4 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?

42. Chapter 17 Section4 Electric Circuits 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.

43. Section4 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.

44. Section4 Electric Circuits Chapter 17

45. Section4 Electric Circuits Chapter 17 Parts of an Electric Circuit, continued • A Switch to Control a CircuitSometimes, a circuit also contains a switch. A switch is used to open and close a circuit.

46. Section4 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 CircuitsSeries 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.

47. Section4 Electric Circuits Chapter 17 Types of Circuits, continued • Parallel CircuitsA parallel circuit is a circuit in which loads are connected side by side. • Uses for Parallel CircuitsAlmost all appliances are built with parallel circuits so that they will keep working if part of the system fails.

48. Section4 Electric Circuits Chapter 17 Household Circuit Safety • Circuit FailureBroken wires or water can cause a short circuit. In a short circuit, charges do not go through one or more loads in the circuit. • FusesA fuse has a thin strip of metal. Fuses keep charges from flowing if the current is too high.

49. Section4 Electric Circuits Chapter 17 Household Circuit Safety, continued • Circuit BreakersA circuit breaker is a switch that automatically opens if the current is too high. Charges stop flowing. • Electrical Safety TipsDo not overload circuits by plugging in too many electrical devices. Do not use electrical devices near water.

50. Chapter 17 Introduction to Electricity Concept Mapping Use the terms below to complete the Concept Mapping on the next slide.