Ch18_RabinR

toc = Chapter 18: Static Electricity = http://www.physicsclassroom.com/Class/estatics/

Guiding Questions (#1-9)
9/7/2011 1. What is the structure and properties of an atom? An atom has three subatomic particles: protons, electrons and neutrons. Protons and neutrons are located in the nucleus while the electrons are located in the electron shells. Protons are positively charged, electrons are negatively charged, and neutrons are neutral. Atom has 0 charge while ions have a charge (cation is positive, anion is negative). To make an atom negative you add an atom and to make an atom positive you take away an atom. 2. What is the symbol and unit of electric charge? Coulombs (Symbol = Q, q); Qe = -1.6 x 10-19 C, Qp = +1.6 x 10 -19 C 3. Distinguish between positive and negative charges in as many ways as possible. Positive: Ions are much bigger than electrons, larger mass, possesses more protons than electrons, tightly bound within the nucleus and immobile. Negative: Electrons, smaller mass, possesses more electrons than protons, electrons can constantly move from atomic environments 4. Describe the properties of electric forces. Particles with the same charge will repel each other while those with opposite charges will attract each other. 5. Distinguish between insulators and conductors. Insulators are materials that prevent EASY flow of electrons from atom to atom (does not permit electrons entirely). Conductors are materials that allow electrons to flow easily from atom to atom. 6. What is polarization? Polarization is the process of separating opposite charges by inducing movement of electrons within an object. 7. How does a neutral object acquire charge? Induced polarization 8.Distinguish between the 3 charging processes. Friction - involves the transfer of electrons between two objects resulting in a positive negative charge, induction - acquires the opposite charge from charging object, conduction - acquires same charge as the charging object. 9. What is the law of electric charge? All magnetic objects have the tendency to repel or attract on another, the attraction/repulsion occurs in a straight line, there is a force between the charges and the bigger the charges the gretaer the force.

Practice Problems (#1-4)
9/8/2011 1. What is the charge on a rod that has 15 excess electrons? 2. What is the charge on a pith ball that has 3.15 x 1016 electrons? 3. How many electrons are missing from a balloon that has a charge of 4.19 x 10-5 C? 4. If a metal object receives a positive charge, does its mass increase, decrease, or stay the same? What happens to its mass if the object receives a negative charge?

Lesson 1 Summary
METHOD 2A: DIRECTED READING - 9/8/2011 After reading the material, answer the following questions: 1. What (specifically) did you read that you already understood well from the class discussion? Describe at least 2 items fully. Previous to reading this lesson, I had a good grasp on the structure of the atom in part due to our class discussion. It was very clear to me that the two subatomic particles, the protons and the neutrons, made up the nucleus while a third subatomic particle, the electron, lived in the atoms electron shells. In addition, after our class discussion I had a good understanding of the differences between protons and electrons. Aside from the proton's positive charge and the electron's negative charge, they also have a drastic difference in size. The electron is extremely small compared to the size of the proton and also has the ability to move from one atomic environment to another. 2. What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding? Before reading lesson 1 the concept of electrons mobility was not very clear to me. I did not understand how electrons could move from atom to atom with absolutely no affect to its shape, size, or function. The examples of the common activities such clothes trembling in a washing machine helped in my understanding. As the laundry twists and twirls, rubbing against one another, electrons too move from the atoms on one article of clothing to the atoms of another. I have now realized the true insignificance electrons have on atoms and the objects they make up. 3. What (specifically) did you read that you still don't understand? Please word these in the form of a question. What is the concept of induced electrons in conducting objects? 4. What (specifically) did you read that was not gone over during class today? We have yet to discuss polarization in class however, I briefly read about this process in the lesson. I currently know that it is the process of separating opposite charges within an object and involves inducing the movement of electrons.

Lesson 2 Summary
METHOD 2A: DIRECTED READING - 9/9/2011 After reading the material, answer the following questions: 1. What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully. Charging by induction and conduction are two processes that I understood well from our class discussion. Charging by induction involves an object acquiring the opposite charge of the charging object while charging by conduction involves an object acquiring the same charge as the charging object. 2. What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding. During our class discussion, charging by friction was only briefly mentioned and aside from rubbing to form the friction, I did not understand the process within the atoms entirely. I now understand that as the two objects rub together, the object with the greater electron affinity takes the electrons from the other object and acquires the negative charge. At the same time, the object that the electrons are coming from becomes charged positively. 3. What (specifically) did you read that you still don’t understand? Please word these in the form of a question. I understood everything I read in Lesson 2 of the physics classroom. 4. What (specifically) did you read that was not gone over during class today? The law of conservation of charge was not gone over today during class. This law states that the charge is always conserved. Although electrons may move from object to object, the total amount of charge amidst the objects before the process starts is the same after the process ends.

Lab: Sticky Tape
9/12/2011 OBSERVATIONS DISCUSSION QUESTIONS 1. Explain how materials become charged through their interaction with one another. Materials become charged through three charging processes: friction, induction, and conduction. Friction occurs by rubbing two objects together (Ex. Step #14 Rubbing the PVC rod with the animal skin) creating a positive charge in one object and a negative charge in the other. Induction involves a grounding wire attached to a neutral object. A charged object is then held towards the neutral object and the like charges repel to the opposite side. This charging results in the objects having the same charge. Conduction however involves the objects acquiring opposite charges. A charged object is moved towards a neutral object forcing the like charges to move to one side of the object. The object with the opposite charge is then attracted to the moving object. 2. Why, when you stroke a cat's fur, or comb your hair on a cold, dry day can you hear a crackling sound? Doing these things in a darkened room, you can actually see sparks. Explain. As the friction begins, static electricity builds up creating a positive charge on one object and a negative charge on the other. The crackling sound and/or the sparks in a darkened room are actually the electrons moving from the negative object to the positive one. 3. Photocopying machines use the principles of electric charges. Do research to find out how photocopying machines work. Be sure to list your sources Copy machines work by using a process called xerography which is very similar to principles behind electrical charges. A copy machine has a special type of film called a photoreceptor and when it gets charged up it can "Erase" the charge by shining light on it. WHen you go to make your copy, electricity causes the air to form lots of positive charges that are sprayed onto the photoreceptor. Then, a beam of light is used to write on the photoreceptor. Where this sheet writes depends on the original piece of paper you placed into the copier. Toner is then shaken over the photoreceptor which has a negative charge and sticks to the positive charges that were left on the photoreceptor. The piece of paper is then pressed against the photoreceptor printing the content from the original sheet of paper onto the new. http://www.ccmr.cornell.edu/education/ask/index.html?quid=87 4. Materials have a characteristic which evaluates their attraction for electrons. The Triboelectric Series orders materials by their affinity for gathering electrons through contact from other materials. The materials toward the top of the list are likely to give up electrons in these interactions whereas those at the bottom are more likely to gain electrons. Five materials are ranked as follows, with more positives meaning least desiring electrons. PVC(++), Wool (+++++), Styrene (++++), Teflon (+), Polyester (+++) a) Rank the materials on the scale below: Loves to Accept Electrons -Teflon -PVC -Polyester -Stryrene -Wool Gives Away Electrons b) Determine the net charge on each item when the following pairs of materials are rubbed together. (In other words, which ends up giving up electrons and which ends up accepting them?) -PVC (-) and Wool (+) -PVC (+) and Teflon (-) -PVC (-) and Polyester (+) -Teflon (-) and Polyester (+) -Styrene (-) and Wool (+)

Practice Problems (#5-7,12)
9/13/2011 1. A 4.5 x 10-9 C charge is located 3.2 m from a –2.8 x 10-9 C charge. Find the electrostatic force exerted by one charge on the other. 2. What is the magnitude and direction of the force between two identical 10 microcoulomb charges 0.015-m apart? 3. Consider the electric force between a pair of charged particles a certain distance apart. By Coulomb's law: a) If the charge on one of the particles is doubled, the force is //_.// b) If, instead, the charge on both particles is doubled, the force is //_.// c) If instead the distance between the particles is halved, the force is //_.// d) If the distance is halved, //and// the charge of both particles is doubled, the force is ___ as great. 12. If two negative charges are held close together, how will the charges move when released?

Lesson 3 Summary
METHOD 2A: DIRECTED READING - 9/13/2011 After reading the material, answer the following questions: 1. What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully. One thing I read that I fully understood during the class discussion was how to find the force between two objects. To do this I use the Coulomb's Law Equation which is. F is the Force, K is a proportionality constant known as Coulomb's law constant, Q1 is the charge of one object, Q2 is the charge of the other object, and d is the distance between the two objects. It is vital to remember that Q1 and Q2 are both absolute values and therefore whether the charge is positive or negative is irrelevant in finding the force. Another aspect of the reading that I fully understood during class was the explanations of charge interaction as forces. I know that even though objects do not touch each other, the attraction and repulsing are still forces. 2. What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding. While doing the practice problems during class, I simply did not understand the relationships between the different variables in some of the problems. After reading the section titled Inverse Square Law, I now understand that the force between two objects is inversely related to the distance between two objects. The chart below helps verify that as the distance increases the force decreases. 3. What (specifically) did you read that you still don’t understand? Please word these in the form of a question. I understood everything I read in Lesson 3 of the Physics Classroom. 4. What (specifically) did you read that was not gone over during class today? We did not discuss whether or not an object was at static equilibrium.

Textbook Problems (Pg 368 - 369 #22, 17, 18)
9/14/2011

Guiding Questions (#10-15)
10. What is an electric field? Through a field force, charged objects can attract and repel without any physical contact. The area in which these forces exist is known as an electric field which is an alteration of the space in the region that surrounds it. Any other charge in the area will feel the force created in the electric field; The region or space around a charge where another charge will feel an electrostatic force. 11. What are the characteristics and properties of an electric field? See applet: [] 12. What are the “players” involved in an electric field? Charge that is the source of the field, charge that is experiencing the field. When the magnitude of source goes up, the field goes up while the magnitude of the experiencing charge goes up, the field goes down because now it is bigger and has less an influence on each other. Closer in distance, the stronger the force. E = Fe/q (E = electric field) 13. What are electric field lines? Electric field lines are patterns of several lines that extend between infinity and the source charge. They point in the direction that a positive test charge would accelerate if placed upon the line thus the lines are directed away from positively charged source charges and toward negatively charged source charges. 14. What are 4 characteristics of electric field lines? -Lines directed from a positively charged object to a negatively charged object, from a positively charged object to infinity, or from infinity to a negatively charged object. -No intersecting line -Most dense around objects with greater charge, more lines the stronger the field is -Lines are perpendicular to surface when they come out of the object 15. Go to []. Scroll to the bottom of the page and do the “Check Your Understanding” questions. 1) C, D, and E 2) Intersecting lines 3) D 4) DAEBC 5) A = +, B = -, C = +, D = -, E = -, F = +, G = +, H = +, I = + 6) B < A, C < D, G < E < F, J< H < I

Activity: Balloon Charges
9/15/2011

Practice Problems (#9,10, 13)
9/15/2011

Lesson 4 Summary
Method 1: Rules-Based Summaries

The concept of a field force is utilized by scientists to explain this rather unusual force phenomenon that occurs in the absence of physical contact. While all masses attract when held some distance apart, charges can either repel or attract when held some distance apart. A charged object creates an electric field - an alteration of the space in the region that surrounds it. Other charges in that field would feel the unusual alteration of the space. The strength of an electric field as created by source charge Q is inversely related to square of the distance from the source. This is known as an inverse square law. Electric field strength is location dependent, and its magnitude decreases as the distance from a location to the source increases. The magnitude of the electric field vector is calculated as the force per charge on any given test charge located within the electric field. The force on the test charge could be directed either towards the source charge or directly away from it. Electrostatic equilibrium is the condition established by charged conductors in which the excess charge has optimally distanced itself so as to reduce the total amount of repulsive forces. Once a charged conductor has reached the state of electrostatic equilibrium, there is no further motion of charge about the surface.


 * An electric field is the altered space created between two charged objects. Any other object in the field feels either an attraction or repulsion based on their charge. Electric field lines surround the charged objects with four main characteristics that must be followed. Towards negatives, away from positives, no intersections, ect.**

Practice 133 (#19)
9/16/2011

Practice Problems (#15, 17)
9/19/2011