CH18_ThorwarthS

=toc Lab: Sticky Tape = // 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). //
 * OBSERVATIONS: (Note: # refers to step in the procedure.) **


 * #5: Sketch with labeled force vectors for two top tapes

close enough to affect each other.

T <-- slightly repelled --> T || Sketch with labeled force vectors for two top tapes half as far apart as left sketch

T <-- repelled --> T ||
 * #8: Describe paper on paper interaction

There was no visible electric force between the two pieces of paper.

P <-- N/A --> P || #9: Describe foil on foil interaction

There was no apparent electric force between the two pieces of foil.

F <-- N/A --> F ||
 * #13: Describe top tape and foil interaction

There was no visible electric force between the top tape and the foil.

Diagram with forces

T <-- N/A --> F || Describe top tape and paper interaction

There was no visible force between the top tape and the paper.

Diagram with forces

T <-- N/A --> P ||
 * #13: Describe top tape and top tape interaction

There was no visible interaction.

Diagram with forces

T <-- N/A --> T || Describe top tape and bottom tape interaction

There is an attraction between the top and bottom tapes.

Diagram with forces

T <-- attraction --> B ||
 * #13: Describe bottom tape and foil interaction

There was a very strong attraction between the bottom tape and the foil.

Diagram with forces B --> very strong attraction < -- F || Describe bottom tape and paper interaction

There was a strong attraction between the bottom tape and the paper.

Diagram with forces

B --> strong attraction <-- P ||


 * #13: Describe bottom tape and top tape interaction

There was some attraction between the bottom and top tapes.

Diagram with forces

B --> attraction <-- T || Describe bottom tape and bottom tape interaction

There was a slight and noticeable attraction between bottom tape and bottom tape.

Diagram with forces

B --> Slight attraction <-- B ||
 * #14: Describe PVC rod and paper interaction

There was a strong attraction between the rubbed PVC and the paper. || Describe PVC rod and foil interaction

There was a strong attraction between the PVC and the foil. ||
 * #14: Describe PVC rod and top tape interaction

There was a strong attraction between the PVC and the top tape. || Describe PVC rod and bottom tape interaction

There was a strong attraction between the PVC and the bottom tape. ||
 * #15: Describe Lucite rod and paper interaction

There was a strong attraction between the Lucite and the paper. || Describe Lucite rod and foil interaction

The strongest attraction noticed was between the Lucite rod and the foil. ||
 * #15: Describe Lucite rod and top tape interaction

There was a strong attraction between the Lucite rod and the top tape. || Describe Lucite rod and bottom tape interaction

There was a strong attraction between the Lucite rod and the bottom tape. ||
 * #16: State top and top tape interaction based on charge

The two top tapes should have like charges and therefore repel from one another. || State top and bottom tape interaction based on charge

The top and bottom tape should have opposite charges and therefore attract. ||
 * #16: State bottom and bottom tape interaction based on charge

The two bottom tapes should have like charges and therefore repel. ||  ||


 * Discussion Questions: **


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


 * Materials become charged through the exchange of electrons with another object. This can be done through friction (as in this lab), induction, or conduction. Through these methods, electrons are exchanged between objects in a way that is uneven, and causes one to become more positively charged, while the other becomes more negatively charged.


 * In this specific lab the friction between the two tapes separating caused electrons to be suddenly exchanged between the two strips. As a result one strip became positive and the other became negative. The PVC and Lucite rods were charged by their friction with the animal furs, which caused electrons to be exchanged as well.


 * 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.


 * The crackling sound and slight sparks are caused by the exchanging of electrons through friction. The electrons ‘jump’ from one surface to another, creating a sound or even sparks through an electrical current of electrons moving.


 * 1) Photocopying machines use the principles of electric charges. Do research to find out how photocopying machines work. Be sure to list your sources.


 * In a photocopying machine, there is a special type of film called a photoreceptor. This photoreceptor can be positively charged up, and wherever light hits it will lose its charge. A light is shown through one side of the paper and hits the photoreceptor where there are no letters or numbers. Where the light does not hit on the photoreceptor remains charged, and a negatively charged black or colored powder called toner will stick to the positively charged parts of the photoreceptor. Once this is done, blank paper is pressed against the photoreceptor and the toner appears on the paper. The paper is then heated so that the toner melts permanently into the paper, creating a copy.


 * This information was brought to you by the Cornell Center for Materials Research at http://www.ccmr.cornell.edu/education/ask/index.html?quid=87

PVC(++), Wool (+++++), Styrene (++++), Teflon (+), Polyester (+++)
 * 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:



<-- (loves to accept electrons) Teflon PVC polyester Styrene Wool (Gives away electrons) -->


 * 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 will give its electrons to wool.

2. PVC and Teflon

Teflon will give its electrons to PVC

3. PVC and Polyester

PVC will give its electrons to Polyester

4. Teflon and Polyester

Teflon will give its electrons to Polyester

5. Styrene and Wool

Wool will give its electrons to Styrene

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.
 * Conclusion: **

Notes 9/16
= Lesson 4: Electric Fields =

4.1: Action at a Distance

Action at a distance is a force that has an affect on objects, even with a distance between the two objects involved, the author claims that action-at-a-distance forces include electric forces and gravity, and that the space around the objects involved is altered because of these forces. 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 **. The action-at-a-distance nature of the electrical force is commonly observed numerous times during lab activities and demonstrations in a Physics classroom. A charged plastic golf tube might be held above bits of paper on a lab bench. The plastic tube attracts the paper bits even though physical contact is not made with the paper bits. The charged plastic tube exerts its influence over a distance, affecting other charged objects that were in the surrounding //neighborhood//. The charged object affects other charged objects that were in the surrounding //neighborhood//. 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. Space is altered by the presence of a charged object. Other objects in that space experience the strange and mysterious qualities of the space.

4.2: Electric Field Intensity

Electric Field Intensity is the magnitude of the forces involved in an electric field on a charged object, and the author claims that electric field intensity is determined by the charge of the source charge, as well as the distance between the object and the source charge. Electric field strength is [|a vector quantity]; it has both magnitude and direction. The magnitude of the electric field strength is defined in terms of how it is measured. Let's suppose that an electric charge can be denoted by the symbol ** Q **. This electric charge creates an electric field; since ** 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 electric field strength is not dependent upon the quantity of charge on the test charge. 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. But according to [|Coulomb's law], more charge also means more electric force (** F **). In fact, a twofold increase in ** q ** would be accompanied by a twofold increase in ** F **. 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.

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. And by whatever factor the distance is changed, the electric field strength will change inversely by the square of that factor.

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. The worldwide convention that is used by scientists is to define the direction of the electric field vector as the direction that a **positive test charge** is pushed or pulled when in the presence of the electric field. A positive source charge would create an electric field that would exert a repulsive affect upon a positive test charge. On the other hand, a positive test charge would be attracted to a negative source charge.

4.3: Electric Field Lines


 * Electric field lines are lines drawn from source charges which indicate the pull of the electric field on a positive experimental charge at every location positive around the source charge. **** Electric field lines ** point in the direction that a positive test charge would accelerate if placed upon the line. As such, the lines are directed away from positively charged source charges and toward negatively charged source charges. One common convention is to surround more charged objects by more lines. Objects with greater charge create stronger electric fields. Not only does the density of lines surrounding any given object reveal information about the quantity of charge on the source charge, the density of lines at a specific location in space reveals information about the strength of the field at that location. A second rule for drawing electric field lines involves drawing the lines of force perpendicular to the surfaces of objects at the locations where the lines connect to object's surfaces.A final rule for drawing electric field lines involves the intersection of lines. Electric field lines should never cross.

Suppose that there are two positive charges - charge A (QA) and charge B (QB) - in a given region of space. Each charge creates its own electric field. Since electric field is a vector, the usual operations that apply to vectors can be applied to electric field. That is, they can be added in head-to-tail fashion to determine the resultant or net electric field vector at each location. Ultimately, the electric field lines surrounding the configuration of our two charges would begin to emerge. For the limited number of points selected in this location, the beginnings of the electric field line pattern can be seen.

4.4: Electric Fields and Conductors


 * According to the author, Electrostatic equilibrium is when a conductive object has as many electrons within it as possible. According to the author, the electrons become as spread out as possible along the surface and inside the object is a net charge of 0. **** 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. One characteristic of a conductor at electrostatic equilibrium is that the electric field anywhere beneath the surface of a charged conductor is zero. A second characteristic of conductors at electrostatic equilibrium is that the 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. 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. The curvature of a surface can range from absolute flatness on one extreme to being curved to a // blunt // point on the other extreme.

4.5: Lightning

Lightning is the transfer of electrons from the negatively charged pole of the cloud to the surface of the earth. The lightning itself, according to the author, is the exchange of millions of electrons in a very short period of time. The precursor of any lightning strike is the [|polarization] of positive and negative charges within a storm cloud. The tops of the storm clouds are known to acquire an excess of positive charge and the bottoms of the storm clouds acquire an excess of negative charge. Two mechanisms seem important to the polarization process. 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. Rising moisture encounters cooler temperatures at higher altitudes. These cooler temperatures cause the cluster of water droplets to undergo freezing. The frozen particles tend to cluster more tightly together and form the central regions of the cluster of droplets. The frozen portion of the cluster of rising moisture becomes negatively charged and the outer droplets acquire a positive charge. Air currents within the clouds can rip the outer portions off the clusters and carry them upward toward the top of the clouds. The frozen portion of the droplets with their negative charge tends to gravitate towards the bottom of the storm clouds. In the end, a storm cloud becomes polarized with positive charges carried to the upper portions of the clouds and negative portions gravitating towards the bottom of the clouds.

Normally, the air surrounding a cloud would be a good enough [|insulator] to prevent a discharge of electrons to Earth. Yet, the strong electric fields surrounding a cloud are capable of ionizing the surrounding air and making it more conductive. The ionization involves the shredding of electrons from the outer shells of gas molecules. The 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 **. 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. The quantity of positive charge residing on the Earth's surface becomes even greater. This charge begins to migrate upward through buildings, trees and people into the air. This upward rising positive charge - known as a ** 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. The enormous and rapid flow of charge along this pathway between the cloud and Earth heats the surrounding air, causing it to expand violently. The expansion of the air creates a shockwave that we observe as thunder.

Tall buildings, farmhouses and other structures susceptible to lightning strikes are often equipped with ** lightning rods **. The first of Franklin's two proposed theories is often referred to as the ** lightning dissipation theory **. According to the theory, the use of a lightning rod on a building protects the building by preventing the lightning strike. The idea is based upon the principle that the [|electric field strength is great around a pointed object]. The second of Franklin's proposed theories on the operation of the lightning rod is the basis of the ** lightning diversion theory **. The lightning diversion theory states that a lighting rod protects a building by providing a conductive pathway of the charge to the Earth. Lightning researchers are now generally convinced that the lightning dissipation theory provides an inaccurate model of how lightning rods work. Unfortunately, there are currently no scientifically verified methods of lightning prevention.

Notes 9/14
HW packet #17,18, and 19

17)

==

18) 19.)

= Lesson 3: Electric Force = Coulomb's Law of Electric Force
 * The three variables that affect electric force are charge, charge, and distance. The force is determined by the charge of the two different objects involved, as well as their distance away.
 * The equation of Coulomb's Law is F = (k x Q 1 x Q 2 ) / d 2 Q = charge of either object k= 9 x 10 9 Nm 2 /C 2

Inverse Square Law
 * Inverse square relationships are when the decrease of a number increases another number by a square value. For example, electrostatic forces between two points varies inversely with the square of the distance apart.

Newton's Laws and the Electrical Force
 * the force attracting or repelling two charged objects id electrical force.
 * This force follows Newton's Laws of motion. It causes acceleration in objects, such as a balloon.
 * Electrical force is also seen when objects repel, and are at an angle while in static equilibrium. The electrical force causes the objects to stay separated.
 * With three or more charged objects, the equations do not have to be changed!
 * Each force can be treated as a vector, and added to discover where something would move as a result. In four objects, there would be three forces impacting each charged object.

Notes 9/13
Electrostatic forces <-- +Q 1 +Q2 --> k e = 9 x 10 9 Nm 2 /C 2 F e = (k e x |Q| x |Q2|) / d2 *N=F e Q2=C F g = (G x m x m2) / d 2



= Lesson 2: Methods of Charging = 1. Charging by Friction
 * Charging by friction occurs when two different objects are rubbed against one another. The electrons of a less attractive atom will leave for the more attractive atom that it is rubbing against. As a result, the less attractive substance becomes a positive charge and the more attractive substance becomes negatively charged.

The Law of Conservation of Charge
 * every charging process involves a transfer of electrons between two objects. Charge is NOT created from nothing. If some object has a negative charge, it got the electrons from another object. Charge is always conserved. The net charge (sum of charges involved in charging) always remains the same, before and after charging.

2. Charging by Induction
 * A method of charging an object without having it actually touch an other charged object. If two neutral objects are conductors, then they will allow the electrons to move relatively freely, depending on the substance. If two neutral conductors are touching and a charged object comes close to one side of the objects, the electrons will flow accordingly. For example if a negatively charged rod comes close to two touching metal balls, the electrons will flow away from the rod and into the other ball. If the balls are then separated the electrons remain all in the ball farther away from the rod. As a result, one ball is positively charged and the other is negatively charged. (the opposite can be true if a positively charged rod comes close, the electrons move closer to the rod)
 * A 'Ground' is an object that is used to supply or remove electrons during induction. In this case, it was the ball farther away from the rod which acted as a ground. If that sphere was not there, the charge of a single sphere would not change without a ground.

3. Charging by Conduction
 * Involves the contact of a charged object and a neutral object. When a negatively charged object touches a neutral object, for example, the electrons spread out as far as possible amongst the two objects, making them both negatively charged. When a positively charged object touches a neutral object, the electrons again spread out as much as possible and cause both objects to become positively charged. In order for conduction to work, the contact of two objects must be between two conductors so that the electrons may flow.

Grounding
 * Grounding is when something is able to give or remove electrons from a charged object to make it neutral. In order to ground an object, there must be enough electrons to give or take electrons from this object without being affected by the change. It is important that there is a pathway for conducting electrons. If an insulator is between the grounding object and the charged object then there will be no effect.

Notes 9/8
What is the charge on a rod with 15 excess electrons? What is the charge of a pitch ball that has 3.15 x 10 16 electrons? How many electrons are missing from a balloon that has a charge of 4.19 x 10 -5 C
 * 15e x (-1.6 x 10 -19 C)/1e= -2.4 x 10 -18 C
 * 3.15 x 10 16 e x ((-1.6 x 10 -19 C)/1e) = -5.04 x 10 -3 C
 * 4.19 x10 -5 C x (1e/(1.6 x 10 -19 C)) = 2.62 x 10 14 e

= = = Guiding Questions: Electric Charge, Forces, and Fields =

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? See applet: [|http://www.gel.ulaval.ca/~mbusque/elec/main_e.html] 12. What are the “players” involved in an electric field? 13. What are electric field lines? 14. What are 4 characteristics of electric field lines? 15. Go to []. Scroll to the bottom of the page and do the “Check Your Understanding” questions.
 * An atom consists of a nucleus and electrons.
 * The nucleus is made of Protons and Neutrons bound together. The protons are positively charged and the neutrons have a neutral charge.
 * The electrons orbit the nucleus and are much smaller than the protons and neutrons. They have a negative charge and can be released from the atom if it receives enough energy.
 * A Coulomb is the unit of electric charge.
 * The symbol of a Coulomb is a Q
 * Positive charges are from when there are fewer electrons than protons. A proton is much larger than an electron, and cannot escape from the nucleus.(Ion)
 * Negative charges are from when there are more electrons than protons. Electrons are much smaller than protons and can escape the atom. (electron)
 * Electric forces can have a non-impact influence on other objects.
 * Opposite electric forces attract. (Attractive)
 * Same charged electric forces repel. (Repulsive)
 * Charged and neutral objects can attract.
 * Conductors are materials that allow electrons to flow freely from atom to atom and molecule to molecule. Conductors permit charge to be transferred across the surface of the object.
 * Insulators do not allow electrons to flow freely from atom to atom and molecule to molecule. Charge introduced will remain at the site where the charge was introduced. Charge is rarely distributed evenly across the surface of the object.
 * The build up of positive and negative charges on separate sides of an object. The site of positive charge and negative charge are opposite one another and are called ‘poles’.
 * When a charged object comes near a neutral object, the neutral object polarizes, and creates a positively charged pole and negatively charged pole on opposite sides of the neutral object. The charged object attracts to the pole with an opposite charge from that object.
 * Polarization creates charge in a neutral object WITHOUT removing or adding any electrons. The positive and negative charges separate and create two poles on opposite sides of the object. The charge is not as strong as if an electron were added or removed, but the object will still have an electric force.
 * By giving enough energy to an electron, it will leave an atom and create a positively charged ion. This process removes an electron and creates a strong positive electric force.
 * Some atoms will add more electrons and become a negatively charged ion. This process adds an electron and crea tes a strong negative electric force.
 * The build up of positive and negative charges on separate sides of an object. The site of positive charge and negative charge are opposite one another and are called ‘poles’.
 * When a charged object comes near a neutral object, the neutral object polarizes, and creates a positively charged pole and negatively charged pole on opposite sides of the neutral object. The charged object attracts to the pole with an opposite charge from that object.
 * Polarization creates charge in a neutral object WITHOUT removing or adding any electrons. The positive and negative charges separate and create two poles on opposite sides of the object. The charge is not as strong as if an electron were added or removed, but the object will still have an electric force.
 * By giving enough energy to an electron, it will leave an atom and create a positively charged ion. This process removes an electron and creates a strong positive electric force.
 * Some atoms will add more electrons and become a negatively charged ion. This process adds an electron and creates a strong negative electric force.
 * Opposites attract and likes repel.
 * A change in the area around an object because of its charge.
 * An electric field appears to be the exact same as the space would be without a charged object unless another object is close enough to have an electric force on the first object. Then the electric field will attract and repel objects depending on their charges.
 * The "players" involved in an electric field are a charged object, and other objects within the electric field. Regardless of the charge of the other objects, even if they are neutral, the objects that enter the electric field will feel the effects of the electric field.
 * A pattern of lines that extend between infinity and the source change which show the pull of the object on a positive test charge.
 * Show the direction of pull on a positive test charge. (out of +, into -)
 * Are perpendicular to the surface of the source charge.
 * the number of lines surrounding the object determine how strong the electric force is on charges.
 * Electric field lines never intersect.
 * 1) Diagram D is incorrect because it shows an unequal separation of electric field lines without another point charge to cause it. Diagram C is incorrect because it shows positive test charges going towards a positive source charge. E is incorrect because it shows positive test charges going away from a negative source charge.
 * 2) His drawing of electric field lines is incorrect because he shows electric field lines intersecting.
 * 3) D) It is clear that object B is positive and object A is negative.
 * 4) DAECB from least to greatest. Strength is determined by how close together the electric field lines are at that object.
 * 5) A = + ; B = - ; C = +; D = -; E = -; F = +; G = +; H = +; I = +
 * 6) B<A; C<D; G<E<F; J<H<I