Ch18_IrwinA

__**ELECTRIC CHARGE, METHODS OF CHARGING,**__ __**ELECTROSTATIC FORCE, & ELECTRIC FIELDS**__ toc **__Class Activity 9.6.11- AP Practice Problems #1 & 2__**

**__Guiding Questions:__**
1. What is the structure and properties of an atom? 2. What is the symbol and unit of electric charge? 3. Distinguish between positive and negative charges in as many ways as possible. 4. Describe the properties of electric forces. 5. Distinguish between insulators and conductors. 6. What is polarization? 7. How does a neutral object acquire charge? 8.Distinguish between the 3 charging processes. 9. What is the law of electric charge? 10. What is an electric field? 11. What are the characteristics and properties of an electric field? 12. What are the “players” involved in an electric field? 13. What are electric field lines? 14. What are the 4 characteristics of electric field lines? 15. Go to []. Scroll to the bottom of the page and do the “Check Your Understanding” questions.
 * //Atoms have electrons that occupy regions of space whose shape is described by complex mathematical equations.//
 * dense nucleus, with protons and neutrons, surrounded by free flowing electrons
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">atoms = no charge
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">ions = charge (cations positive, anions negative)
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">electronegativity is how much an atom attracts electrons
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Coulomb = unit of charge
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Q or q is the symbol for charge
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">One electron (Q sub e) = -1.60 x 10^-19 C
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">One proton = +1.60 x 10^-19 C
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Positive Charges:
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">ions
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">ions are much bigger than electrons because it has ions on it, plus the nucleus
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">mass of an ion is a lot (more than 10,000x more massive than electron)
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">protons cannot move (jiggle within the nucleus) (immobile)
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Negative Charges:
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">electrons
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">much smaller than ions
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">mass of an electron is a little m = 9.11 x 10^-31 kg
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">electrons are very mobile, free to move within their electron cloud
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Opposite charges will attract
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Like charges will repel
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Charged objects exert a force on both charged and uncharged objects.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Conductors are materials that permit electrons to flow freely from atom to atom and molecule to molecule. An object made of a conducting material will permit charge to be transferred across the entire surface of the object.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons; subsequently charge is seldom distributed evenly across the surface of an insulator.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Polarization is the process of separating opposite charges within an object. The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Induced polarization (a perceived overall loss or gain of electrons)
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 19px;">The frictional charging process results in a transfer of electrons between the two objects that are rubbed together.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Induction charging is a method used to charge an object without actually touching the object to any other charged object.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%; line-height: 19px;">Charging by Conduction means that the two objects will come into actual physical contact with each other.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">All magnetic objects have the tendency to repel or attract to one another. Like charges repel one another and unlike charges attract one another.
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">The attraction or repulsion occurs in a straight line, there is a force between the charges and the bigger the charges the greater the force
 * It is a region around a charge where the electric force can be felt by another object (this region exists whether or not the other charge is there to experience the force).
 * The strength of the electric field is dependent on the strength of the object's charge.
 * Source field
 * Experiencing charges
 * Distance between the above two
 * Electric field lines are lines on which the electric potential is constant.
 * The path a charge would follow if it were allowed to move along in exactly the direction of the force acting on it.
 * they cannot intersect
 * The bigger the charge, the more forceful the lines
 * They are perpendicular to the surface of the source
 * (Positive in, negative out) Lines directed from a positively charged object will go to a negatively charged object; lines from a positively charged object will go to infinity; or lines from infinity will go to a negatively charged object.
 * C,D,E
 * Electric field lines cannot intersect
 * A=negative, B=positive
 * D, A, E, C, B
 * A, C, F, G, H, I are positive
 * B<A; C<D; G<E<F; J<H<I

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**__ Practice Questions: __**
 * <span style="font-family: Arial,Helvetica,sans-serif;">1. What is the charge on a rod that has 15 excess electrons?
 * <span style="font-family: 'Comic Sans MS',cursive;">[[image:Screen_shot_2011-09-08_at_2.26.01_PM.png]]
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">2. What is the charge on a pith ball that has 3.15 x 1016 electrons?
 * <span style="font-family: 'Comic Sans MS',cursive; font-size: 14px; line-height: 21px;">[[image:Screen_shot_2011-09-08_at_2.26.12_PM.png]]
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">3. How many electrons are missing from a balloon that has a charge of 4.19 x 10-5 C?
 * <span style="font-family: 'Comic Sans MS',cursive; font-size: 14px; line-height: 21px;">[[image:Screen_shot_2011-09-08_at_2.26.23_PM.png]]
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14px; line-height: 21px;">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?
 * <span style="font-family: 'Comic Sans MS',cursive;">As it loses electrons, mass decreases. As it gains electrons, mass decreases.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Class Notes:__** <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Physics Classroom Summary: Static Electricity Lesson 1__**

 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * I already understood the basic structure and properties of the atom. I knew that an atom is a dense nucleus of protons and neutrons, surrounded by electrons in electron shells. I knew that atoms do not have a charge, while ions do. I knew that the number of protons determines the type of element an atom is. I knew that the mass & size of a proton is much greater than the mass & size of an electron. I also understood how protons and electrons have equal magnitudes of charge, but that the charges are opposite.
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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.
 * The reading helped me to understand our activity with the electric force. I understood that by rubbing the felt on the rods we were creating a charge, but I did not understand how it would cause the uncharged objects (animal fur and hanging object) to move. The explanation that "any charged object can exert this force upon other objects - both charged and uncharged objects" clarified why the fur and hanging object reacted.
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
 * In class I was a little confused about the difference between Q and coulomb. From the reading I think I understand that Coulombs is the unit that describes quantity of the charge (Q). Is that correct?
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What (specifically) did you read that was not gone over during class today?
 * <span style="font-family: Arial,Helvetica,sans-serif;">Polarization and polar bonds were not gone over in class today.

Follow Up Notes (from class):
 * polarization is when you make a neutral object have a charge
 * first step to the two other types of charging (conduction and induction)
 * bring a negative rod into contact with object, the negatives will go to one side and the new ones will come over, you acquire the same charge as the charging object
 * perceived imbalance, there are more positive or negatives on one side
 * CONDUCTION:
 * [[image:Photo_on_2011-09-09_at_14.30.jpg]]
 * INDUCTION:
 * [[image:Photo_on_2011-09-09_at_14.35.jpg]]
 * Conductors lose their electrons more easily, allow them to leave and come in easily
 * Insulators hold electrons more, resist gaining and losing electrons
 * anything can be a conductor with enough voltage

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Physics Classroom Summary: Methods of Charging Lesson 2: 9/11/11__**

 * 1) What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * I already knew that there were three methods of charging: friction, induction, and conduction. From the Quia activity homework and from our discussion I understood that it is the electrons that move during the charging process. I knew that in charging by friction, the objects touch and in charging by induction and conduction the objects do not. These processes all create the appearance of a charge.
 * 1) 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.
 * I did not understand using the two spheres for induction during class. Now I understand that the second sphere is used the same way a grounding wire is used.
 * 1) What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
 * Why is a pathway necessary? How come the straw does not have the same grounding effect as the finger?
 * 1) What (specifically) did you read that was not gone over during class today?
 * We did not go over the labs explained in the reading.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Sticky Tape Lab: 9/12/11__**
__**Materials**:__ -tape, foil, paper, PVC rod, plastic strips
 * __Objectives:__**
 * 1) How do different materials react in the presence of a charged object?
 * 2) How do you distinguish between positively and negatively charged objects?
 * 3) How do you determine the exact net charge on an object?

__**Observations:**__ __**Discussion Questions:**__ PVC(++), Wool (+++++), Styrene (++++), Teflon (+), Polyester (+++)
 * 1) Explain how materials become charged through their interaction with one another.
 * In this activity the objects were charged by friction. As we pulled the pieces of tape apart or rubbed the rods with fur, some of the objects became positive by losing electrons, while others became electrons by gaining electrons.
 * 1) 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 various objects make contact, electrons are transferred. The crackling noise and sparks signify this transfer of electrons.
 * 1) Photocopying machines use the principles of electric charges. Do research to find out how photocopying machines work. Be sure to list your sources.
 * An image is projected onto a drum (which has a positive charge). This drum conducts electricity when under light. The toner has a negative charge and is attracted to the positively charged parts of the drum (where the outline of the image is). The drum rotates and imprints the image onto a piece of paper. By heating the paper the image is “fixed” onto the paper permanently.
 * http://www.gcsescience.com/pse10-electrostatic-photocopier.htm
 * 1) 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.
 * 1) Rank the materials on the scale below:

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Physics Classroom Summary: Electric Force Lesson 3: 9/13/11__**

 * 1) What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * I already understood that like charges repel and that opposite forces attract, and that when these interactions occur the objects exert an equal force on each other. I knew that this force can be measured in Newtons.
 * 1) 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.
 * I didn't fully understand that the relationship between electrostatic force and distance is inverse square. The reading really clarified that.
 * 1) What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
 * What are point charges?
 * 1) What (specifically) did you read that was not gone over during class today?
 * We did not discuss when an object is considered to be in equilibrium.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Class Activity 9/14/11:__**

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Class Activity 9/15/11: Balloon Charges__**
<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;"> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Electric Field Notes:__** <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;"> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;"> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Practice #133__** <span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Physics Classroom Summary: Electric Fields Lesson 4__**
<span style="font-family: Arial,Helvetica,sans-serif;">How can an object be charged and what affect does that charge have upon other objects in its vicinity? There are two categories of forces - contact forces and non-contact forces. Electrical force and gravitational force were both listed as non-contact forces. Gravitational forces are action-at-a-distance forces that act between two objects even when they are held some distance apart. The charged object affects other charged objects that were in the surrounding //neighborhood//. Action-at-a-distance forces are sometimes referred to as field forces. 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. Whether a charged object enters that space or not, the electric field exists. A Van de Graaff generator is 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. Some electric fields are stronger or more intense than others.Electric field strength is a vector quantity; it has both magnitude and direction. The strength of the source charge's electric field could be measured by any other charge placed somewhere in its surroundings. The charge that is used to measure the electric field strength is referred to as a test charge since it is used to //test// the field strength. When placed within the electric field, the test charge will experience an electric force - either attractive or repulsive. The magnitude of the electric field is simply defined as the force per charge on the test charge. E=F/q (Newton/Coulomb) Increasing the quantity of charge on the test charge - say, by a factor of 2 - would increase the denominator of the equation by a factor of 2. So as the denominator in the equation increases by a factor of two (or three or four), the numerator increases by the same factor. These two changes offset each other such that one can safely say that the electric field strength is not dependent upon the quantity of charge on the test charge. So regardless of what test charge is used, the electric field strength at any given location around the source charge ** Q **will be measured to be the same. If the expression for electric force as given by Coulomb's law is substituted for force in the above E =F/q equation, a new equation can be derived as shown below. E=(k*Q/d^2). This electric field strength formula is that it illustrates an inverse square relationship between electric field strength and distance. Electric field strength is location dependent, and its magnitude decreases as the distance from a location to the source increases. (E1/E2) = (d2^2/d1^2). 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.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 19px;">**__Class Notes 9/19/11: Concept Map__**

 * 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

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