CH18_ListroR

Ch. 18: Electric Charge, Methods of Charging, Electrostatic Force, and Electric Fields toc

= Guiding Questions: Electric Charge, Forces, and Fields = > The nucleus, possessing the majority of the mass, contains neutrally charged neutrons and positively charged protons. Negatively charged electrons are located on the outside in orbitals. Atoms are neutrally charged, with ions being positive or negative. > Q, q ; Coloumb > Positive: loses electrons, more than 10,000 times more massive than e-, immobile   Negative: more electrons than protons, 9.11x10 -31 kg, mobile > Oppositely charged particles attract, while similarly charged particles repel. Neutrally charged particles stand indifferent, unless when charged particles attract them. > Insulators don’t allow electrons to move easily. Conductors allow them to move easily. > Opposites attract and likes repel. > A neutral object and a negatively changed object are held close to each other. Negatives in the neutral object go to other side. Half of the object seems positive and the other side vice versa. > It will use its electron affinity to possess electrons from other objects. > Friction: Electrons rub off of one object and onto another, creating an imbalance of electrons within both of the objects. > Induction : negative object gets close to neutral object, and becomes polarized. There is a grounding wire touching the neutral object. The negatives will continue through the wire and leave to go to the ground. This leaves a completely positive charge, and acquires the opposite charge from the charging object. For the opposite situation, a positive charging object will draw in electrons from the wire. > Conduction: i f negative object touches polarized object, negatives move to once-neutral object. Results in same charge as charging object. > The net charge between two objects that have just gained opposite charges stays the same as it was before they were charged. Charge is neither created nor destroyed; it is transferred. > - Anywhere beneath the surface of a conductor, the electric field is zero. > - Electric fields are perpendicular to the surface. > - Electric fields are strongest at points where the surface is most curved (pointed) > There is a source of field, which gives off the field lines. Its charge is represented by Q. There are also experiencing charges. There can be multiple experiencing charges and they can vary in size. They feel the effects of the electric field. Their charge is represented by q. > The are visual representations of the forces of electric fields. > 1. In C, the lines are directed towards a positively charged object. In D, the lines are not symmetrically positioned despite the fact that the object is a symmetrical sphere. In E, the lines are directed away from a negative charge. > 2. Electric field lines should never intersect each other. Erin crossed his lines. > 3. D- Electric field lines are directed towards object A so object A must be negative. They are directed away from object B so object B must be positive. > 4 **.** DAECB- Electric field strength is greatest where the lines are closest together and weakest where lines are furthest apart. > 5. Objects A, C, F, G, H, and I are positively charged. Objects B, D and E are negatively charged. The principle is: electric field lines always approach negatively charged objects and are directed away from positively charged objects. > 6. B < A; C < D; G < E < F; J < H < I = Practice Questions = = Charge and Charge Interactions = What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * 1) What is the structure and properties of an atom?
 * 1) What is the symbol and unit of electric charge?
 * 1) Distinguish between positive and negative charges in as many ways as possible.
 * 1) Describe the properties of electric forces.
 * 1) Distinguish between insulators and conductors.
 * 1) What is the law of electric charge?
 * 1) What is polarization?
 * 1) How does a neutral object acquire charge?
 * 1) Distinguish between the 3 charging processes.
 * 1) What is an electric field?
 * 1) What are the characteristics and properties of an electric field? See applet: []
 * 1) What are the “players” involved in an electric field?
 * 1) What are electric field lines?
 * 1) What are 4 characteristics of electric field lines?
 * Electric field lines always extend 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.
 * Electric field lines never cross each other.
 * Electric field lines are most dense around objects with the greatest amount of charge.
 * At locations where electric field lines meet the surface of an object, the lines are perpendicular to the surface.
 * 1) Go to []. Scroll to the bottom of the page and do the “Check Your Understanding” questions.
 * 1) How is electric force computed using the superposition principle?
 * 2) What are the properties of an isolated conductor?
 * 3) Explain how lightning occurs and lightning rods work. Use any reference you would like, but be sure to note down the bibliographical information.
 * 4) Summarize the Millikan Oil Drop Experiment, using a labeled diagram. See applet: []
 * 5) Describe how a Van De Graaff generator works.


 * Conduction: if negative object touches polarized object, negatives move to once-neutral object. Results in same charge as charging object. **Negatives can only move
 * Induction: negative object gets close to neutral object, and becomes polarized. There is a grounding wire touching the neutral object. The negatives will continue through the wire and leave to go to the ground. This leaves a completely positive charge, and acquires the opposite charge from the charging object. For the opposite situation, a positive charging object will draw in electrons from the wire.

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. N/A

What (specifically) did you read that you still don’t understand? Please word these in the form of a question. How does polarization occur? Conductor vs. insulator?
 * From Class: A neutral object and a negatively changed object are held close to each other. Negatives in the neutral object go to other side. Half of the object seems positive and the other side vice versa.
 * From class: insulators don’t allow electrons to move easily. Conductors allow them to move easily.

What (specifically) did you read that was not gone over during class today? N/A

= Methods of Charging = What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * Electron affinity is the property of an electron that describes how much an atom wants to gain an electron. When two objects are rubbed together, atoms with a higher affinity will pull off electrons from atoms with a lower one. This affinity is presented in the Triboelectric Series, which lists which materials have a higher affinity. The net charge will always be the same before and after friction occurs.
 * Charging by induction involves two objects that do not touch each other. If there are 2 neutral spheres directly next to each other, and a negative rod is held close to the spheres, the electrons will move away from the rod. Once the spheres are then moved apart, the sphere farthest from the rod will be negatively charged and the other will be positively charged. A grounding wire can also be used for the electrons to escape the atoms.

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. N/A

What (specifically) did you read that you still don’t understand? Please word these in the form of a question. Electrostatic forces?
 * From Class:
 * If they’re both the same charge, they repel
 * F=(kc x abs(q1) x abs(q2))/(d^2)
 * Kc=constant
 * Ending unit is Newtons
 * Repelling: accel.--> veloc.--> (away)
 * Parallel equation to force of gravity
 * Force is relatively strong compared to size of object
 * Electrostatic can attract and repel; gravitation can only attract

What (specifically) did you read that was not gone over during class today? N/A

= Electric Force = What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. Its equation is [[image:listro_coloumb_equation.png width="81" height="29"]], k being a constant, q1 and q2 being the absolute value of the two objects’ charges, and d being the distance the objects are apart from each other. This law is accurate in displaying the point charges (as if the charge is located in the center).
 * The equation used in Coulomb’s law is comparative to that of gravitational force. Both equations have an inverse square relationship between force and separation distance. They are different in the constants, which show that the Coulomb's law constant (k) is significantly greater than Newton's universal gravitation constant (G). Also, gravitational forces are only attractive; electrical forces can be either attractive or repulsive.

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. N/A

What (specifically) did you read that you still don’t understand? N/A

What (specifically) did you read that was not gone over during class today? N/A

= Sticky Tape Lab = Group: Eric Solomon, Ryan Listro Assigned: September 12, 2011

Observations:

Discussion Questions:

1. Explain how materials become charged through their interaction with one another.

The two pieces of tape, the PVC rod, and the Lucite rod all became charged through friction. Due to movement between these objects, friction occurred, thus allowing the objects to share electrons with the object it was rubbing against. This creates a positively charged object and a negatively charged object. Conduction, which involves a charged object moving towards a neutral object and results in forcing like charges to move to one side of the object, occurred when charged objects such as tape and rods were moved towards neutral objects such as foil and paper. Induction was not experienced during the lab but it requires a grounding wire that allows electrons to escape a neutral object when a charged object is moved towards it.

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.

This occurs because you are creating friction between your hand and a cat's fur. When this occurs, static electricity builds up and creates a positive charge on one object and a negative on the other. The sound and sparks that result from this are 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 known as xerography. They have a a special film known as a photoreceptor, which when charged, can erase a charge by shining light upon it. When copying, the machine's electricity causes the air to form positive charges, which are spread onto the photoreceptor. A beam of light is then used to write on the photoreceptor; the location of the writing depends on the original paper placed into the copier. Toner, which has a negative charge, is then shaken over the sheet and sticks to the positive charges left on the photoreceptor. The piece of paper is then pressed onto the photoreceptor, which, in turn, presses the content from the original piece of paper onto the copying paper. []

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 (+++)
 * Rank the materials on the scale below:
 * Loves to Accept Electrons
 * Teflon
 * PVC
 * Polyester
 * Stryrene
 * Wool
 * Gives Away Electrons
 * 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 (+)

= ClassWork: 9/14 = = Balloon Activity = = = = Electric Fields = In Class: Summary: forces are referred to as field forces. ** field force ** is used to explain this unusual force phenomenon that occurs in the absence of physical contact. charges can either repel or attract when held apart. there is something strange about the space surrounding a charged object. It creates an electric field - an alteration of the space in the region that surrounds it. Other charges would feel the unusual alteration of the space. experienced first hand by the use of a Van de Graaff generator, a large conducting sphere that acquires a charge as electrons are scuffed off of a rotating belt as it moves past sharp elongated prongs inside the sphere. On a dry day, the buildup of charge becomes so great that it can exert influences on charged balloons held some distance away. the strength of the electric field is dependent upon the amount of charge that creates the field and the distance from the charge.

Electric field strength is a vector quantity.


 * Q ** is the source of the electric field, refered to it as the **source charge**. The strength could be measured by any other charge placed somewhere in its surroundings. The charge used to measure the electric field strength is a ** test charge **. denoted by the symbol ** q **. it will experience an electric force - either attractive or repulsive.

electric field strength is not dependent upon the quantity of charge on the test charge.

Electric field strength is location dependent, and its magnitude decreases as the distance from a location to the source increases.

Field Lines:


 * electric field lines **, point in the direction that a positive test charge would accelerate if placed upon the line. lines are directed away from positively charged source charges and toward negatively charged source charges.

Principles:


 * Electric field lines always extend 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.
 * Electric field lines never cross each other.
 * Electric field lines are most dense around objects with the greatest amount of charge.
 * At locations where electric field lines meet the surface of an object, the lines are perpendicular to the surface.

= Class Work: 9/16 =

= Class Work: 9/19 =


 * Electric field = 0 on the inside of a shape
 * All excess charges are on the inside of the shape only
 * the field points at right angles towards the surface
 * the pointier the surface, the more excess charges