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Electricity Chapter 14. Section 2 Electric Charge and Static Electricity Objectives Explain the role of charged particles in atoms and in charged objects.

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Presentation on theme: "Electricity Chapter 14. Section 2 Electric Charge and Static Electricity Objectives Explain the role of charged particles in atoms and in charged objects."— Presentation transcript:

1 Electricity Chapter 14

2 Section 2 Electric Charge and Static Electricity Objectives Explain the role of charged particles in atoms and in charged objects. Describe how electric force depends on charge and distance. Describe three ways in which an object can become charged. Compare conductors with insulators. Give two examples of static electricity and electric discharge. Chapter 14

3 Section 2 Electric Charge and Static Electricity Electric Charge Charges And Forces Atoms are composed of particles with electric charge. The law of electric charges states that like charges repel and opposite charges attract. When you rub you hair on a balloon, why will it stick to the wall? Imbalance of charges Hair becomes negative (more electrons) Balloon becomes positive (fewer electrons) Chapter 14

4 Section 2 Electric Charge and Static Electricity Chapter 14 The Structure of an Atom

5 Size of the Charges The unit of measure for electrical charge is the Coulomb Electrons and Protons have the same charge, but opposite –Electrons have a charge of -1.6x C –Protons have a charge of +1.6x C

6 Section 2 Electric Charge and Static Electricity 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. Chapter 14

7 Section 2 Electric Charge and Static Electricity The Law of Electric Charges Chapter 14

8 Section 2 Electric Charge and Static Electricity Charge It! Friction Charging by friction happens when electrons are “wiped” from one object onto another. Like a balloon through your hair Conduction Charging by conduction happens when electrons move from one object to another by direct contact. Like touching the handle of a door after shuffling your feed Induction Charging by induction happens when charges in an uncharged metal object are rearranged without direct contact with a charged object. Chapter 14

9 Section 2 Electric Charge and Static Electricity Chapter 14

10 Section 2 Electric Charge and Static Electricity Charge It!, continued Chapter 14 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.

11 Charging by Contact Section 2 Electric Charge and Static Electricity Chapter 14

12 Section 2 Electric Charge and Static Electricity Moving Charges Chapter 14 Conductors An electrical conductor is a material in which charges can move easily. Silver, gold, copper are best Most other metals Insulators An electrical insulator is a material in which charges cannot move easily Air, cloth, paper, plastic, wood.

13 Section 2 Electric Charge and Static Electricity Static Electricity Chapter 14 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.

14 Section 2 Electric Charge and Static Electricity How Lightning Forms Chapter 14

15 Section 2 Electric Charge and Static Electricity Static Electricity, continued Chapter 14 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.

16 Electric Force The attraction of a positively charged particle to a negatively charged particle Electric force is proportional to charge and distance –Force is equal to the product of the charges (F e =C a C b ) –Force is inversely proportional to the SQUARE of the distance F e =1/(d a -d b ) 2 If you double the distance, the force is one-fourth If you half the distance, the force is 4 times

17 Electric Force Electric Force acts in a ‘Field’ –Electric Field is the area in which the oppositely charged items attract each other

18 Section 3 Electric Current and Electrical Energy 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 response in your science journal. Chapter 14

19 Section 3 Electric Current and Electrical Energy Objectives Describe electric current. Describe voltage and its relationship to electric current. Describe resistance and its relationship to electric current. Explain how a cell generates electrical energy. Describe how thermocouples and photocells generate electrical energy. Chapter 14

20 Section 3 Electric Current and Electrical Energy 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. Chapter 14

21 Section 3 Electric Current and Electrical Energy 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. Chapter 14

22 Section 3 Electric Current and Electrical Energy Electric Current, continued Alternating Current and Direct Current There are two kinds of electric current—direct current (DC) and alternating current (AC). Chapter 14

23 Section 3 Electric Current and Electrical Energy 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. Chapter 14

24 Section 3 Electric Current and Electrical Energy 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. Chapter 14

25 Section 3 Electric Current and Electrical Energy 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. Chapter 14

26 Section 3 Electric Current and Electrical Energy Resistance and Temperature In general, the resistance of metals increases as temperature rises. Chapter 14 Resistance, continued

27 Chapter 14 Factors That Affect Resistance Section 3 Electric Current and Electrical Energy

28 Generating Electrical Energy Cells change chemical or radiant energy into 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. Chapter 14

29 Section 3 Electric Current and Electrical Energy How a Cell Produces an Electric Current Chapter 14

30 Section 3 Electric Current and Electrical Energy 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. Chapter 14

31 Magnetism and Electricity Use the terms below to complete the concept map on the next slide. Concept Mapping electric current battery charges thermocouple photocell cell Chapter 14

32 Magnetism and Electricity Chapter 14

33 Magnetism and Electricity Chapter 14

34 End of Chapter 14 Show Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

35 FCAT For the following questions, write your answers on a separate sheet of paper. Chapter 14 Standardized Test Preparation

36 1. Charged particles in solar wind bombard Earth constantly. The image below shows how the paths of these charged particles are bent as they approach Earth. What causes the charged particles in the solar wind to change course as they approach Earth? A.Earth’s gravity B.Earth’s radiation C.Earth’s electric field D.Earth’s magnetic field Chapter 14 Standardized Test Preparation

37 1. Charged particles in solar wind bombard Earth constantly. The image below shows how the paths of these charged particles are bent as they approach Earth. What causes the charged particles in the solar wind to change course as they approach Earth? A.Earth’s gravity B.Earth’s radiation C.Earth’s electric field D.Earth’s magnetic field Chapter 14 Standardized Test Preparation

38 2. Several forces act on the objects in the image below. One force pushes the objects apart. Another force pulls the object together. What force pulls the two objects toward each other? F.gravity G.convection H.electric force I.magnetic force Chapter 14 Standardized Test Preparation

39 2. Several forces act on the objects in the image below. One force pushes the objects apart. Another force pulls the object together. What force pulls the two objects toward each other? F.gravity G.convection H.electric force I.magnetic force Chapter 14 Standardized Test Preparation

40 3. After sliding down a plastic slide, Juan notices the hairs on his arm are standing on end. Which of the following forces pushes the hairs up? A.atomic force B.electric force C.magnetic force D.gravitational force Chapter 14 Standardized Test Preparation

41 3. After sliding down a plastic slide, Juan notices the hairs on his arm are standing on end. Which of the following forces pushes the hairs up? A.atomic force B.electric force C.magnetic force D.gravitational force Chapter 14 Standardized Test Preparation

42 4. George wants to generate electrical energy in his house from a renewable resource. What device from the following choices could he use as a model? F.a nuclear power plant G.a coal fired power plant H.a diesel electric generator I.a solar roadside emergency phone Chapter 14 Standardized Test Preparation

43 4. George wants to generate electrical energy in his house from a renewable resource. What device from the following choices could he use as a model? F.a nuclear power plant G.a coal fired power plant H.a diesel electric generator I.a solar roadside emergency phone Chapter 14 Standardized Test Preparation

44 5. The sketch below shows a diagram of Angelica’s experiment. Angelica placed the “black box” in a hot attic during the day and observed the light bulb shining brightly. During the night, the light bulb went out. Part A Identify the type of energy going into the light bulb that was generated by this system. Part B Explain why the light bulb went out at night. Chapter 14 Standardized Test Preparation

45 5. Part A Identify the type of energy going into the light bulb that was generated by this system. Part A: Full-credit answers should include the following points: light bulbs are powered by electrical energy; the black box in the attic must generate electrical energy; the black box generates electrical energy from the thermal energy in the hot attic. Part B Explain why the light bulb went out at night. Part B: Full-credit answers should include the following points: at night, the sun does not warm up the attic; there is not enough thermal energy in the attic at night for the black box to generate the electrical energy required to illuminate the light bulb. Chapter 14 Standardized Test Preparation

46 Section 1 Magnets and Magnetism Chapter 14

47 Section 1 Magnets and Magnetism Chapter 14

48 Section 1 Magnets and Magnetism Chapter 14

49 Section 1 Magnets and Magnetism Chapter 14

50 Section 1 Magnets and Magnetism Chapter 14

51 Section 2 Electric Charge and Static Electricity Chapter 14 The Structure of an Atom

52 Section 2 Electric Charge and Static Electricity The Law of Electric Charges Chapter 14

53 Section 2 Electric Charge and Static Electricity Chapter 14

54 Section 2 Electric Charge and Static Electricity Chapter 14

55 Section 2 Electric Charge and Static Electricity How Lightning Forms Chapter 14

56 Section 3 Electric Current and Electrical Energy Chapter 14

57 Section 3 Electric Current and Electrical Energy Chapter 14

58 Section 3 Electric Current and Electrical Energy Chapter 14

59 Section 3 Electric Current and Electrical Energy Chapter 14

60 Section 3 Electric Current and Electrical Energy How a Cell Produces an Electric Current Chapter 14

61 Section 3 Electric Current and Electrical Energy Chapter 14

62 Standardized Test Preparation

63 Chapter 14 Standardized Test Preparation

64 Chapter 14 Standardized Test Preparation


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