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Static Electricity Slide 2 Water and Static Electricity Video on http://cjschroeder.wikispaces.com Video on http://cjschroeder.wikispaces.comhttp://cjschroeder.wikispaces.com Slide 3 What is Electricity? Historical Ideas The ancient Greeks knew about static electricity and the existence of 2 types of charge. The ancient Greeks knew about static electricity and the existence of 2 types of charge. In the 1700s there was an emerging idea that some items were electrics (they attracted objects when rubbed) and others were non- electrics (did not attract objects when rubbed) In the 1700s there was an emerging idea that some items were electrics (they attracted objects when rubbed) and others were non- electrics (did not attract objects when rubbed) No one could explain why! No one could explain why! Slide 4 Charge is the name we apply to the property, and objects can be charged by friction Charge is the name we apply to the property, and objects can be charged by friction Charge gives rise to forces of attraction and repulsion Charge gives rise to forces of attraction and repulsion Observing attraction and repulsion, we can say that two charge states exist Observing attraction and repulsion, we can say that two charge states exist Slide 5 Opposites Attract Charges that are like (that is, created in similar circumstances) repel Charges that are like (that is, created in similar circumstances) repel Charges which are unlike (that is, created in different circumstances) attract A neutral object is attracted to both positive and negative charges A neutral object is attracted to both positive and negative charges Slide 6 Charles du Fay (1698 1739) A French physicist A French physicist Began his experiments in the 1700s Began his experiments in the 1700s Discovered that a cork ball touched by an electrified glass rod would attract another cork ball touched by an electrified resin rod. Discovered that a cork ball touched by an electrified glass rod would attract another cork ball touched by an electrified resin rod. Slide 7 Two Fluid Theory His results led du Fay to conclude that there were two kinds of electric fluids His results led du Fay to conclude that there were two kinds of electric fluids 1. Vitreous Electricity 1. Vitreous Electricity 2. Resinous Electricity 2. Resinous Electricity Slide 8 The Two Fluid Theory Says 1. All objects contain both fluids 1. All objects contain both fluids 2. An electrically neutral object has equal amounts of vitreous and resinous fluids. 2. An electrically neutral object has equal amounts of vitreous and resinous fluids. 3. An object is vitreous if it has more vitreous fluid and resinous if it has more resinous fluid 3. An object is vitreous if it has more vitreous fluid and resinous if it has more resinous fluid 4. When two objects come into contact with each other the fluids transfer from one object to another to balance out and become electrically neutral. 4. When two objects come into contact with each other the fluids transfer from one object to another to balance out and become electrically neutral. Slide 9 The Problem What happens when two vitreous objects touch? What happens when two vitreous objects touch? What happens when two resinous objects touch? What happens when two resinous objects touch? Why do objects attract and repel each other? Shouldnt everything attract everything else if everything contains both fluids? Why do objects attract and repel each other? Shouldnt everything attract everything else if everything contains both fluids? Slide 10 Benjamin Franklin Began studying electricity in 1752. Began studying electricity in 1752. Rejected du Fays two fluid theory. Rejected du Fays two fluid theory. Franklin was the first to use the terms positive and negative to describe electricity. Franklin was the first to use the terms positive and negative to describe electricity. Slide 11 One Fluid Theory Franklin proposed that there is only one electrical fluid and an object is positively or negatively charged depending on how much fluid it has. Franklin proposed that there is only one electrical fluid and an object is positively or negatively charged depending on how much fluid it has. A neutral object has just enough fluid A neutral object has just enough fluid A positive object has too much fluid A positive object has too much fluid A negative object has too little fluid A negative object has too little fluid Slide 12 How the one fluid theory solves the problems of the two fluid theory Positive and negative objects attract each other because the extra fluid from the positive object flows into the negative object Positive and negative objects attract each other because the extra fluid from the positive object flows into the negative object Like charges repel because: Like charges repel because: 1. A positive charged object wont take the extra electrical fluid from another positive object 1. A positive charged object wont take the extra electrical fluid from another positive object 2. A negative charged object doesnt have extra fluid to give to another negative charged object 2. A negative charged object doesnt have extra fluid to give to another negative charged object Slide 13 A Modern Look at Electricity Slide 14 The Modern Atomic Theory ( A review of Atoms and Elements) 1. Atoms are made up of positive particles called protons, negative particles called electrons and neutral particles called neutrons. 1. Atoms are made up of positive particles called protons, negative particles called electrons and neutral particles called neutrons. 2. Protons and neutrons are found in the nucleus of the atom while electrons orbit around the nucleus 2. Protons and neutrons are found in the nucleus of the atom while electrons orbit around the nucleus 3. Atoms are electrically neutral so: 3. Atoms are electrically neutral so: The # of protons = The # of electrons The # of protons = The # of electrons Slide 15 The Particle Model of Electric Charge Developed from 20 th century experimentation. This is the model currently accepted as correct. Developed from 20 th century experimentation. This is the model currently accepted as correct. This theory states that charge is a result of the presence of protons and electrons. This theory states that charge is a result of the presence of protons and electrons. Slide 16 The 3 Electrical States According to the particle model of electric charge, an object can exist in 3 electrical states. According to the particle model of electric charge, an object can exist in 3 electrical states. 1. An object can be Neutral 1. An object can be Neutral # of protons = # of electrons # of protons = # of electrons 2. An object can be Positive 2. An object can be Positive more protons than electrons more protons than electrons 3. An object can be Negative 3. An object can be Negative More electrons than protons More electrons than protons Slide 17 Neutrons are found in the nucleus where they are fixed and cannot move Neutrons are found in the nucleus where they are fixed and cannot move Since protons (+) are found in the nucleus they are fixed and cannot move. Since protons (+) are found in the nucleus they are fixed and cannot move. Electrons (-) are moving around the nucleus and as a result are free to move. Electrons (-) are moving around the nucleus and as a result are free to move. Slide 18 Neutral Attraction Bring a positively charged rod near bits of paper, and the paper will be attracted to the rod Bring a positively charged rod near bits of paper, and the paper will be attracted to the rod However, the paper is not negatively charged! However, the paper is not negatively charged! How do we know? If the paper was negatively charged, then the bits of paper would be repelling each other How do we know? If the paper was negatively charged, then the bits of paper would be repelling each other Bring a negatively charged rod near the paper, and the paper will be attracted to the rod Bring a negatively charged rod near the paper, and the paper will be attracted to the rod Slide 19 Conductors Substances that allow electrical charge to pass through them easily. Substances that allow electrical charge to pass through them easily. Conductors have electrons that are not tightly held by their nuclei which allows electrons to move easily. Electrons are able to flow Conductors have electrons that are not tightly held by their nuclei which allows electrons to move easily. Electrons are able to flow Examples Examples Metals Metals Ions in water Ions in water The human body The human body Slide 20 Insulators Substances that do not allow electric charge to pass through them easily. Substances that do not allow electric charge to pass through them easily. Insulators have electrons that are more strongly attached to their nuclei. Insulators have electrons that are more strongly attached to their nuclei. Examples Examples Glass Glass Plastics Plastics Water Water Air Air Slide 21 Charging by Friction An object can be charged by rubbing it (friction) because this action can cause the electrons to be pulled off of or deposited onto the object An object can be charged by rubbing it (friction) because this action can cause the electrons to be pulled off of or deposited onto the object The electrons are unable to flow and therefore the transferred electrons will stay where they are placed. The electrons are unable to flow and therefore the transferred electrons will stay where they are placed. Slide 22 Electron Affinity The transfer of electrons is determined by the Electron Affinity of the object. The transfer of electrons is determined by the Electron Affinity of the object. When 2 objects are rubbed together, the object with the highest Electron Affinity will take electrons from the other object becoming negative. When 2 objects are rubbed together, the object with the highest Electron Affinity will take electrons from the other objec