Ch19_SolomonE

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= = =** Chapter 19: **= = =
 * Electric Potential and Capacitance **

= = = = = = The capacity for an object to perform a task = = = = The exertion of force in order to perform a task/overcome any resistence = = = = Energy is conserved when none is lost due to heat and moves out of a given system. In general, energy just changes forms though and is always conserved. = = = = Conservative- When energy is stored = = Non-conservative- When energy is not stored = = = = Electrostatic force is the force produced by a charged object. It is conservative = = = = W= E*q*d = =
 * 1) Review what you know about energy from last year’s notes! Also look in the Cutnell and Johnson text and on The Physics Classroom.
 * 1) What is energy?
 * 1) What is work?
 * 1) When is energy conserved?
 * 1) What is the difference between conservative and non-conservative types of forces and energies?
 * 1) What is electrostatic force? Is it conservative or nonconservative?
 * 1) Combine the equations for work and for electric field strength to get a new expression for work.
 * 1) In a uniform electric field, a charge moves from one place to another. What are the only types of energy present in this situation?

Kinetic energy and electrical potential energy


 * 1) Use this to find an expression for the change in potential energy.

U=q(v1-v2)


 * 1) Check this out! Real footage of So Cal Edison opening a switch on a 500kV line while its under load to make repairs. Turn it up, the sound is cool. []

Wow!

6. What is the definition of potential difference? What is the equation, symbol and unit of potential difference? Why is potential difference a relative value, not an absolute value? = = Potential difference- voltage = = V= (change in)PE/q = = Potential difference is measured in voltage = = It is a relative value b/c it is a value of difference and not the total energy = = = Lab: = What is the relationship between electric field lines and equipotentials? AP Physics

Prelaboratory Assignment In an analysis of electric field lines and equipotentials, we will find that the voltage will either increase or decrease noticeably directly surrounding the charge depending on whether the charge forming the field lines is positive or negative.
 * 1) The objective is stated in the title. What is your hypothesis? (Attempt to answer the question, to the best of your knowledge.)


 * 1) What is the rationale for your hypothesis? (Provide detailed reasoning here. This may take the form of a list of what you already know about the topics, with a summary at the end.)
 * Electrons form charges (either excess or lack thereof)
 * Electrons are attracted to positive charges
 * Higher the magnitude of the charge, the farther away from normal it will be
 * At a positive charge, the voltage will be higher because it will have a greater ability to repel a positive test charge

Using a multimeter to measure voltage and testing different scenarios in terms of charges used and their orientation
 * 1) How do you think you might test this hypothesis? (What might you measure and how?)

Two increases nearest the positive charges An increase near the positive and a decrease near the negative A significant increase near the very center A steady increase from the negative to the positive
 * 1) Predict the electric field lines (and the equipotential surfaces) of the following situations:
 * 2) Two point sources (one positive and one positive)
 * 1) Two point sources (one negative and one positive)
 * 1) A circle (negatively charged) and a positive point charge in the very center of it.
 * 1) Two lines of charge (one negative and one positive)

In this experiment you will be constructing 3-dimensional plots of differently shaped electric fields. To do this you will measure and plot the electric potential between two charged points on a sheet of conductive paper. You will then view the plots from different perspectives.
 * Introduction ** :

|| Volt meter (VOM)
 * Expected Materials ** :
 * Alligator leads (2) || Metal push pins (2) ||
 * Cork board || Power supply || Silver marker ||

Part A. Preparing the materials 1) Select a sheets with silver conductive lines drawn on it. Use a conductive ink pen to draw one of the given shapes. 2) Place the sheet on the cork pad. Place one metal pin through each of the two painted silver points on the conducting paper. 3) Insert black probe in to COM socket of the voltmeter (VOM) and insert red probe into other Voltmeter socket. Then, set selector to 20V. 4) Set power supply to 20V. Test power supply with VOM to make sure that it is working. 5) Attach one lead wire from the power supply to one metal pin, then attach another wire from the other clip of the power supply to the second metal pin on the corkboard. 6) Attach the black COM wire from the voltmeter to one of the pins.
 * Procedure ** :

//Recording data// 7) Create a numbered grid in Excel using the conducting sheet as a reference. 8) You will only do points 5 to 15 on the vertical axis, and 5 to 20 on the horizontal axis. 9) Touch the red wire from the voltmeter gently to point (5,5). Use the first number that appears on the voltmeter. Enter your data directly into Excel. Move to the next point (5,6). Repeat for all points until you reach (15, 20). 10)Repeat for the other designs.

//Graphing Data// (Please note that these graphs are shared amongst the groups) 11)Highlight entire table 12)Graph a SURFACE 13)Create two views: Side and Top 14)Adjust scale to “2”. (It does “5” as a default.) 15)If graph is not relatively smooth, go back and remeasure. 16)Put your name(s), lab title, and date on the header/footer. 17)Email me a copy of your Excel document and I will compile all of them into one document and email them to everyone.
 * 2+ Charges**

These graphs show an increase in voltage clustered around the charges. As predicted, these charges are positive, and therefore have a higher voltage. The cluster is not as significant, though, because of the fact that both charges are positive and will therefore both attract clusters of higher voltage.

The dipole situation shows a cluster of significantly higher voltage around the positive charge, and a significant voltage dip around the negative charge. In this situation, with a negative surrounding area, the positive charge in the center is massively greater than the entire rest of the platform. Here, where parallel charged plates of opposite charge are presented, the positive side receives the majority of the voltage. On the other hand, the negative charge has a much lower voltage than the average. This chart shows a steady climb as well from the negative end to the positive end.
 * Dipole**
 * Circle**
 * Parallel Plates**


 * Data:** (Please note that this data is shared between every group**)**

// Conclusion // In your lab journal, and after discussion with your partners and/or classmates, write a conclusion that addresses each of the following: See individual graphs According to my predictions as well as commonly accepted physics, the results turned out well. The dips and increases in the graphs came out as they should have according to the relativistic nature of voltage. It was correct This would be mainly attributed to human error, a malfunctioning multimeter, or the charges not being accurately recognized. But for the noticeable errors, I only seemed to observe human error’s presence. I would have kept the same procedure. It turned out well, if a bit tedious, in my opinion.
 * What does each graph show?
 * How well did the results turn out? How do you know?
 * Return to your hypothesis and answer it again. Was your initial response correct? If not, where were you wrong? Discuss the correction.
 * What are possible sources of error?
 * What would you do differently if you had to begin this lab all over again? Why?

During this lab, we as a class set out to evaluate the fundamental relationship between equipotentials and electric field lines. The hypothesis, as stated above, referred to the belief that voltage will experience a noticeable change in magnitude surrounding the placement of a known charge. By doing this, each team of students got to work on proving this in a unique scenario. In the first scenario, two positive charges were placed some distance from each other. It was shown, through the usage of a multimeter (this stays constant throughout the experiments), that the voltage (which is a relative value) increased directly surrounding the charges in a conic manner, climaxing on the direct center of the charge. As shown in the dipole scenario, the same happened with the positive charge. As for the negative charge, the voltage was significantly decreased. This would be because of the fact that voltage does not apply the "q," or charge values in Coloumbs, as absolute values. Instead, they are represented //with// their positive/negative signs. This theory was again applied with a central charge, measuring the voltage surrounding in concentric circles. Seeing as the charge was positive, the voltage was a much higher value, again culminating in the very center. In the final scenario, two parallel charges were presented on either side of the circulating mat. As predicted, the voltage was exceptionally higher on the positive side, and exceptionally lower on the negative side. And aside from petty errors, such as the possibilities (although slight to say the least) that every single multimeter malfunctioned in the exact same manner, or that the charges were actually all of the opposite sign, there was no real and noticeable error. In fact, all of the results turned out more or less as planned and as theorized in the original hypothesis. I would say with only the slimmest of doubts that this experiment would absolutely be an effective and repeatable way to prove the principles of electric potential in relation to equipotentials, and would most definitely recommend it for further usage.

= Classwork: =



Electric Current Lesson 1
 * Summary**

Action-at-a-distance forces are sometimes referred to as field forces. The space surrounding a charged object is affected by the presence of the charge; an electric field is established in that space. A charged object creates an electric field - an alteration of the space or field in the region that surrounds it.


 * Electric Field, Work, and Potential Energy **






 * Electric Potential **

Electric Potential Energy is dependent on two things:

1) Electric charge - property of the object experiencing the electrical field

2) Distance from source - location within the electric field

Electric potential is the potential energy per charge. Electric potential is used to express the effect of an electric field in terms of the location within the electric field.




 * Electric Potential Difference **

E lectric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy



Unit of electrical potential difference is the volt, V. Volt is equivalent to one Joule per Coulomb.


 * Electric Potential Difference and Simple Circuits **

As the positive test charge moves through the //external circuit// from the positive terminal to the negative terminal, it decreases electric potential energy and is at low potential by the time it returns to the negative terminal. If a 12 volt battery is used in the circuit, then every coulomb of charge is gaining 12 joules of potential energy as it moves through the battery. Every coulomb of charge loses 12 joules of electric potential energy as it passes through the external circuit. The loss of electric potential energy in the external circuit results in a gain in light energy, thermal energy and other energy.

The cells supply the energy to do work upon the charge to move it from the negative terminal to the positive terminal. The cell is capable of maintaining an electric potential difference across the two ends of the external circuit. Once the charge has reached the high potential terminal, it will naturally flow through the wires to the low potential terminal. In a battery-powered electric circuit, the cells serve the role of the charge pump.

The ** internal circuit ** is the part of the circuit where energy is being supplied to the charge. The ** external circuit ** is the part of the circuit where charge is moving outside the cells through the wires on its path from the high potential terminal to the low potential terminal.