Ch18_Demberro

=toc It's Electric=

Guiding question
1. What is the structure and properties of an atom? It has positively charged protons, and neutral neutrons in middle nucleus. Electrons encompass around it. Atoms are neutral unless it has a charge and becomes an ion. 2. What is the symbol and unit of electric charge? Coulomb and (C) is unit of charge. (Q or q)   3. Distinguish between positive and negative charges in as many ways as possible. Positive charges lose electrons, while negative charges gain electrons. Protons are tightly bound in the nucleus and take place. Electrons are more free flowing and substantially smaller (10,000 times less. Positive charges are also ions. Negative charges are electrons   4. Describe the properties of electric forces.   It is noncontact. Opposites attract, likes repel, neutral attract both positive and negative.    5. Distinguish between insulators and conductors.   Insulators impede flow of electrons, conductors allow them. Electrons thusly can flow through conductors yet cannot do so through insulators.    6. What is polarization?   Polarization is separating positive from negatives and vice versa.

7. How does a neutral object acquire charge? Comes in contact with an electron or loses one.

8. Distinguish between the 3 charging processes. Conduction- touching together of two objects. Electrons will either be added or taken away from the touching of two.. Induction- no contact. Can be from the ground where electrons leave object and go to ground. Object acquires opposite charge from charging object. Can be from third object touching second. Polarization is when an object "teases" positives or negatives to repel thus making a negative and positive part of an atom.

9. What is the law of electric charge? There are three charges: positive, negative and neutral.

Practice Questions
 * 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?

**Summary Lesson 1**
I understood the piece about charges of electrons with coulombs when it mentions how electrons and neutrons have the same magnitude of charge as well as the mathematical relationship between electrons and coulombs. In that section I also understood why electrons are gained or lost to make ions as changing protons would make it a completely new type of atom.
 * What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.**

I was wondering why neutrons were not discussed based on the fact that being neutral they can still attract positives and negatives. I now understand that they serve a function unrelated to how neutral objects react with positive and negative and that I should not consider them to be significant in this lesson.
 * 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.**

How do objects that polarize not react like a typical situation when electrons are engaged with protons?
 * What (specifically) did you read that you still don’t understand? Please word these in the form of a question.**

Polar bonds in water and how they relate to polarization and charges.
 * What (specifically) did you read that was not gone over during class today?**

Summary Lesson 2
Charging by induction= opposite charge. Charging by conduction= Acquires same charge. None. How does charging by friction differ from conduction if both deal with coming into direct contact with another object? 4. What (specifically) did you read that was not gone over during class today? Law of charging was not discussed too much, but like every science law charges cannot be destroyed or created, only transferred and replaced.
 * 1) What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * 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.
 * 1) What (specifically) did you read that you still don’t understand? Please word these in the form of a question.

Lab: Sticky Tape
**Hypothesis- Materials will be either attracted or repelled by a charged object depending on their own charge. Likes will attract, opposites will repel, and neutral objects will attract to positive or negative and do nothing to another neutral object.** **You distinguish between positively and negatively charged objects by finding an object that you know is positive or negative and see if a charged object will attract or repel.** **You will know the net charge on the object since the law of charges states electrons cannot be created or destroyed. Therefore the total charge of a system must be zero, so knowing the other charges can help. Furthermore, the chemistry of atoms means they will take enough to have a full outer shell, so knowing how many electrons the atom needs to do so can be known, and using the conversion to coloumbs will give the answer.**

// NOTE: All observations should be written on the attached summary pages. Label forces with simple arrows, and interactions as “attracted”, “repelled”, or “N/A” (nothing apparent). // close enough to affect each other. Force from right tape Force from left tape || Sketch with labeled force vectors for two top tapes half as far apart as left sketch || **N/A** || #9: Describe foil on foil interaction **N?A** || Diagram with forces || Describe top tape and paper interaction Diagram with forces || Diagram with forces || Describe top tape and bottom tape interaction Diagram with forces || Diagram with forces || Describe bottom tape and paper interaction Diagram with forces ||
 * OBSERVATIONS: (Note: # refers to step in the procedure.) **
 * #5: Sketch with labeled force vectors for two top tapes
 * #8: Describe paper on paper interaction
 * #13: Describe top tape and foil interaction
 * Attract**
 * Attract**
 * #13: Describe top tape and top tape interaction
 * Repel**
 * Attract**
 * #13: Describe bottom tape and foil interaction
 * Attract**
 * Repel**

Diagram with forces l || Describe bottom tape and bottom tape interaction Diagram with forces || **Strong Attract** || Describe PVC rod and foil interaction **Moderate Attract** || **Weak Attract** || Describe PVC rod and bottom tape interaction **Weak Repel** || **Strong Attract** || Describe Plastic and foil interaction **Strong Attract** || **Repels** || Describe Plastic and bottom tape interaction **Positive** || State top and bottom tape interaction based on charge **Negative** ||
 * #13: Describe bottom tape and top tape interaction
 * Attract**
 * Repel**
 * #14: Describe PVC rod and paper interaction
 * #14: Describe PVC rod and top tape interaction
 * #15: Describe Plastic and paper interaction
 * #15: Describe Plastic and top tape interaction
 * Attract** ||
 * #16: State top and top tape interaction based on charge
 * #16: State bottom and bottom tape interaction based on charge ||  ||


 * Discussion Questions: **

**When objects rub against each other, come into contact, or become induced, the one with a greater electron affinity will take on more electrons and become negative. The one with less electron affinity will lose the electrons and become positive.** **There is frictional charging going on, so electrons are jumping from the fur or hair onto the comb or hand, making the fur or hair positively charged. You see sparks from the static electricity when differently charged objects touch each other the electrons jump from one object to another and create the spark.** **The machine is made out of a drum that can be selectively charged and a black colored toner. An image of what needs to be copied is transformed onto the surface of the drum which becomes charged. Then, the toner is attracted to the drum through static electricity in the positions that represent the image, and heat fuses the toner particles onto the paper to make the copy. The parts that need to be left alone are repelled to leave white.**
 * 1) Explain how materials become charged through their interaction with one another.
 * 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.
 * 1) Photocopying machines use the principles of electric charges. Do research to find out how photocopying machines work. Be sure to list your sources.


 * http://home.howstuffworks.com/photocopier1.htm**

PVC(++), Wool (+++++), Styrene (++++), Teflon (+), Polyester (+++) Loves to Accept-Loves to give away
 * 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:
 * Teflon, PVC, Polyester, Styrene, Wool**.

**Wool gives to PVC**
 * 1) 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?)
 * 2) PVC and Wool

**PVC gives to Teflon**
 * 1) PVC and Teflon

**Polyester gives to PVC**
 * 1) PVC and Polyester

**Polyester gives to Teflon**
 * 1) Teflon and Polyester

**Wool gives to Styrene**
 * 1) Styrene and Wool

Revisit your hypotheses and answer the objectives in light of your observations. Be sure to be specific, supporting your statements with evidence from the lab. My hypothesis was correct for the most part. During the experiment the top tape would always repel the other top tape and attract to either the paper or aluminum. Top would attract to paper and repel aluminum, while bottom would do the opposite (exemplified in the diagrams) since transitive property is backed up where likes repel likes and opposites attract.
 * Conclusion: **

Lesson 3
a) I understand Coulomb's law and equation and how force is increased when charges are increased or the distances are shortened. Further, I understand how charges play a role and that their charges are not important for the equation as opposite charges will attract each other and the same charges will repel each other with the same force given the coulombs and distances are the same. Also, I can see how it mirrors the equation for gravitational force. b) Another thing i understand well from class in the inverse square law and how it applies to the law. Since the distance's square is divided, you are basically multiplying the inverse. Thus, when the distance gets smaller, squaring the value will lead to a dramatic increase in the force (halving the distance will make force 4x bigger, 1/5 distance makes it 25x bigger, etc.) Thinking of charges as forces on each other was a little confusing at first although now i fully see how electrostatic force is a typical force such as gravity and should be treated as such even if it is not as palpable as forces such as tension or normal. N/A Solving for forces in equilibrium, which in a way is already familiar.
 * 1) What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
 * 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.
 * 1) What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
 * 1) What (specifically) did you read that was not gone over during class today?

Guiding Questions 10-15
10. What is an electric field? Area where forces attract and repel without contact. Points in same direction of force, and greater electric field means greater acceleration of electrons along it. 11. What are the characteristics and properties of an electric field? See applet: [] Electric fields rely on position and strength of charge in attracting. 12. What are the “players” involved in an electric field? The source field, experience field, distance between atoms. 13. What are electric field lines? Direction of positive charges that are attracted or repelled by negative charges. 14. What are 4 characteristics of electric field lines? 1. Lines go from positive to negative; infinity to negative, or positive to infinity. NEVER negative to anything. 2. Lines will never intersect. 3. Bigger object, more forceful the lines. 4. Perpendicular to emitting source. 15. Go to []. Scroll to the bottom of the page and do the “Check Your Understanding” questions. Class Activity with Balloons

Practice Problems
13. Three charges are arranged as shown below. Find the magnitude and direction of the electrostatic force on the charge at the origin. Practice 17-19c 19c. What will be the magnitude and direction of the electric field at point x in each of the following diagrams?

Lesson 4 Summary
Part 1 The primary question being addressed in this unit of The Physics Classroom is: How can an object be charged and what affect does that charge have upon other objects in its vicinity? Electric force is an action-at-a-distance force. In Lesson 4 of this unit, we will explore this concept of ** action-at-a-distance ** using a different concept known as the ** electric field **. It was mentioned that 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 An action-at-a-distance or non-contact force is quite unusual. Football players don't run down the field and encounter collision forces from five yards apart. Contact forces are quite usual. Best description of non-contact forces involves the introduction of the concept of ** electric field **. Action-at-a-distance forces are sometimes referred to as field forces. 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. Whether a charged object enters that space or not, the electric field exists. Space is altered by the presence of a charged object. Other objects in that space experience the strange and mysterious qualities of the space. The strength of the electric field is dependent upon the amount of charge that creates the field and the distance from the charge.
 * Action at a Distance **
 * The Electric Field Concept **
 * A Stinky Analogy **

Part 2 Electric field from a numerical viewpoint is the ** electric field strength **.
 * Electric Field Intensity **

Electric field strength is [|a vector quantity]. The magnitude of the electric field strength is defined in terms of how it is measured. ** Q ** is the source of the electric field, we will refer to it as the **source charge**. 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. The test charge has a quantity of charge denoted by the symbol ** q **. When placed within the electric field, the test charge will experience an electric force - either attractive or repulsive. As is usually the case, this force will be denoted by the symbol ** F **. The magnitude of the electric field is simply defined as the force per charge on the test charge. The standard metric units are Newton/Coulomb or N/C. Two charges would always be necessary to encounter a force. In the electric world, it takes two to attract or repel. Electric field is the force per quantity of charge //on the test charge//. The electric field strength is not dependent upon the quantity of charge on the test charge. The charge of the test is in the bottom so it cancels out part of the force. Equation becomes k*Q/(d2).
 * The Force per Charge Ratio **

Part 3 The magnitude or strength of an electric field in the space surrounding a source charge is related directly to the quantity of charge on the source charge and inversely to the distance from the source charge. The direction of the electric field is always directed in the direction that a positive test charge would be pushed or pulled if placed in the space surrounding the source charge. It can be represented by a vector arrow.
 * Electric Field Lines **

A more useful means of visually representing the vector nature of an electric field is through the use of electric field lines of force. E** lectric field lines ** point in the direction that a positive test charge would accelerate if placed upon the line.

There are a variety of conventions and rules to drawing such patterns of electric field lines. The conventions are simply established in order that electric field line patterns communicate the greatest amount of information about the nature of the electric field surrounding a charged object. One common convention is to surround more charged objects by more lines. Objects with greater charge create stronger electric fields. By surrounding a highly charged object with more lines, one can communicate the strength of an electric field in the space surrounding a charged object by the line density. This convention is depicted in the diagram below.
 * Rules for Drawing Electric Field Patterns **




 * 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.

Part 4 A conductor at electrostatic equilibrium is that the electric field anywhere beneath the surface of a charged conductor is zero.
 * Electric Fields and Conductors **
 * 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 and there is no further motion of charge about the surface.
 * Electric Fields Inside of Charged Conductors **

Positives go to negatives on outside, inside is zero. Referred to as a ** Faraday's cage **. This principle of ** shielding ** is commonly utilized today as we protect delicate electrical equipment by enclosing them in metal cases.

Electric field upon the surface of the conductor is directed entirely perpendicular to the surface. There cannot be a component of electric field (or electric force) that is parallel to the surface. The motion of electrons, like any physical object, is //governed// by [|Newton's laws]. One outcome of Newton's laws was that [|unbalanced forces cause objects to accelerate in the direction of the unbalanced force and a balance of forces causes objects to remain at equilibrium].
 * Electric Fields are Perpendicular to Charged Surfaces **

A third characteristic of conducting objects at electrostatic equilibrium is that the electric fields are strongest at locations along the surface where the object is most curved.
 * Electric Fields and Surface Curvature **

A flat location has no curvature.



A charge is seen to interact with an electric field as opposed to with another charge. To Faraday, the secret to understanding action-at-a-distance is to understand the power of charge-field-charge. A charged object sends its electric field into space, reaching from the "puller to the pullee." Each charge or configuration of charges creates an intricate web of influence in the space surrounding it. While the lines are invisible, the affect is ever so real. So as you practice the exercise of constructing electric field lines around charges or configuration of charges, you are doing more than simply drawing curvy lines. Rather, you are describing the electrified web of space that will draw and repel other charges that enter it.
 * Electric Field Lines as an Invisible Reality **

Part five The precursor of any lightning strike is [|polarization] within a storm cloud. Tops are positive, bottom negative. The cloud's [|electric field] stretches through the space surrounding it and induces movement of electrons upon Earth. Electrons on Earth's outer surface are repelled by the negatively charged cloud's bottom surface. This creates an opposite charge on the Earth's surface. As the static charge buildup in a storm cloud increases, the electric field surrounding the cloud becomes stronger. The strong electric fields surrounding a cloud are capable of ionizing the surrounding air and making it more conductive. Gas molecules that compose air are thus turned into a soup of positive ions and free electrons. The insulating air is transformed into a conductive ** plasma **. The ability of a storm cloud's electric fields to transform air into a conductor makes charge transfer (in the form of a lightning bolt) from the cloud to the ground (or even to other clouds) possible. Two steps for lightning. One mechanism involves a separation of charge by a process that bears resemblance to [|frictional charging]. The second mechanism that contributes to the polarization of a storm cloud involves a freezing process.
 * Lightning **

A lightning bolt begins with the development of a ** step leader **. Excess electrons on the bottom of the cloud begin a journey through the conducting air to the ground at speeds up to 60 miles per second. These electrons follow zigzag paths towards the ground, branching at various locations. The quantity of positive charge residing on the Earth's surface becomes even greater. This upward rising positive charge, ** streamer ** - approaches the step leader in the air above the surface of the Earth. Once contact is made between the streamer and the leader, a complete conducting pathway is mapped out and the lightning begins.

9/19
Any hollow box (shape) has Electric Field of zero inside. Most static electricity at tip of shape compared to an oblong area. Concept Map