Ch19LevineE

**9/20-Homework Summary**
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 * Electric Field and the Movement of Charge: A charged object creates an electric field, in which particles naturally move from high to low energy.**

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 is a vector quantity whose direction is defined as the direction that a positive test charge would be pushed when placed in the field.

It is simply natural for objects to move from high energy to low energy; but work is required to move an object from low energy to high energy

work would not be required to move an object from a high potential energy location to a low potential energy location




 * Electric Potential: Electric potential is dependent upon the charge of the object and the distance of the object from the source charge. **

the electric potential is dependent upon the amount of charge on the object experiencing the field and upon the location within the field

Within the electrochemical cells of the battery, there is an electric field established between the two terminals, directed from the positive terminal towards the negative terminal. As such, the movement of a positive test charge through the cells from the negative terminal to the positive terminal would require work, thus increasing the potential energy of every Coulomb of charge that moves along this path.

the chemical energy is used to do work on a positive test charge to move it from the low potential terminal to the high potential terminal. Chemical energy is transformed into electric potential energy within the //internal circuit// (i.e., the battery)




 * Electric Potential Difference: EPD is the voltage between the final and initial location of a charge, work is required to go from low potential to high potential, but not vice versa. **

in moving the charge against the electric field from location A to location B, work will have to be done on the charge by an external force. The work done on the charge changes its potential energy to a higher value; and the amount of work that is done is equal to the change in the potential energy. As a result of this change in potential energy, there is also a difference in electric potential between locations A and B

the electric 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

Because electric potential difference is expressed in units of volts, it is sometimes referred to as the ** voltage **.

Electric circuits are all about the movement of charge between varying locations and the corresponding loss and gain of energy that accompanies this movement.

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. And similarly, every coulomb of charge loses 12 joules of electric potential energy as it passes through the external circuit.

in a battery-powered electric circuit, the cells serve the role of the charge pump to supply energy to the charge to lift it from the low potential position through the cell to the high potential position.

The ** internal circuit ** is the part of the circuit where energy is being supplied to the charge. For the simple battery-powered circuit that we have been referring to, the portion of the circuit containing the electrochemical cells is the internal circuit.

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.

When at the positive terminal of an electrochemical cell, a positive test charge is at a high ** electric pressure **

The loss in electric potential while passing through a circuit element is often referred to as a ** voltage drop **



Classwork














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? 1. potential difference the amount of energy per unit charge needed to move a particle from one point to another 2. it is relative because it depends on the magnitude of the source charge 3. V=E/q (volts)
 * 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.
 * 2) What is energy? **the ability to do work**
 * 3) What is work? **application of a force over a distance**
 * 4) When is energy conserved? **energy is always conserved, it cannot be created or destroyed only transferred to a different form**
 * 5) What is the difference between conservative and non-conservative types of forces and energies? **conservative forces can be stored and preserve the ability to do work. non-conserative forces cannot be stored and cannot preserve the ability to do work**
 * 6) What is electrostatic force? Is it conservative or nonconservative? **Attraction or repulsion of charged particles. It is a conservative force**
 * 7) Combine the equations for work and for electric field strength to get a new expression for work.
 * 8) **W= Ft**
 * 9) **E=Fe/q......Eq=Fe**
 * 10) **W=Eqt**
 * 11) In a uniform electric field, a charge moves from one place to another. What are the only types of energy present in this situation?
 * 12) **electrostatic and kinetic energy**
 * 13) Use this to find an expression for the change in potential energy.
 * 14) **EPE=KeF**
 * 15) 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. []

9/22-Equipotential Surface Lab
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 ||
 * Purpose**: Find the relationship between equipotentials and electric field lines.

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 ** :

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. 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.

The area closest to the positive charges will have the strongest electric potential, the area close to the negative charges have the weakest electric potential, and equipotentials will be the same distance from the electric charges.
 * Hypothesis**

The definition of an equipotential surface is a surface on which electric potential is constant. Also, I know that the Equipotentials will be the same distance form the charge, because distance is a variable that voltage is dependent upon, and the other two variables will remain constant.


 * Data**

Circle- data taken from previous years Data for Circle Graph

The electric potential energy is strongest at the center of the circle, where the charge was placed. The electric potential energy decreases in a concentric fashion the further it gets from the center.

Parallel Plates- data taken from Richie Johnson, Allison Iwrin, and Bret Pontillo. Data for Parallel Plates Graph

Shows a gradual increase in electric potential energy from the negative line to the positive line.

Dipole- data taken from Sam Fihma, Phil Litmanov, and Steven Thorwarth Data for Dipole Graph

The two peaks that can be seen from each view represent the places where the charges were placed. The peak at 20 represents the positive charge, and the peak at 9 represents the negative charge.

2 + Charges- data taken from Chris Hallowell, Ryan Listro, and Eric Solomon. Data for Two Positive Charges Graph

The two peaks that can be seen from each view represent the places where the charges were placed. This is where the electric potential energy is greatest, and then the electric potential energy decreases in concentric circles the further the distance from the charges gets. The level plane in the center is indicative of the repulsion between the two positive charges.


 * Analysis**

2+ Charges This picture if very close to the theoretical version. The lines come out perpendicular to the two charges, and are skewed away from each other because of the repulsion. However, my lines are not as straight as the they should be in theory, and also do not show the full extent of the repulsion.

Dipole This picture shows the general idea of what the electric field lines for a dipole should look like, but does a poor job with accuracy. The lines should run from the positive charge to the negative charge, like shown in the picture above. However the lines should be straighter than depicted, and should also branch out wider. In addition, lines with arrows facing inwards should be placed around the negative charge from the other direction.

Parallel Plates This picture is identical to the theoretical version. The lines travel from positive to negative in a straight line.The lines on the ends should curve outwards a little bit according to the theoretical picture, but do not in my depiction.

Circle This picture is a very close match to the theoretical version. The lines come out perpendicular to the positive charge in all directions. The only small issue with the picture I drew is that the lines are not should be straighter and less curved. Also, the circles depicted on the graph should in theory be perfect circles.
 * Conclusion**

Each graph shows that Electric Potential is greatest closest to the positive charge, least near the negative charges. The data is indicative of this claim because the graphs show the highest level of electric potential where the positive charges were placed, and the lowest level where the negative charges were placed. The graphs also show that the equipotential surfaces are equidistant to the positive and negative charges. The graphs clearly demonstrate this because of their depiction of the equipotential surfaces. For example, in the circle graph, the electric potential is strongest in the middle, and decreases with distance from the positive charge in concentric circles. This shows the trend of electric potential in relation to the charges, and supports my claim about equipotential surfaces. My hypothesis stated that the area closest to the positive charges will have the highest electric potential, the areas closest to the negative charges will have the lowest electric potential, and that equipotentials will be the same distance from the charges. From the graphs and data, I conclude that all parts of my hypothesis were correct. If we reference the circle graph again, this clearly demonstrates the validity of my hypothesis. The electric potential is strongest in the center at the positive charge, and decreases with distance. Additionally, the equipotentials are all equidistant from the positive charge in the center. A possible source of error could be the reading of the volt-meter. The values were constantly changing, and it is possible that we read the data at different times. This would distort our results because of a lack of consistency. Also, we tried to hold the probe exactly perpendicular to the points at each point, but its possible that we failed to do so. Inconsistency in the placement of the probe could lead to distorted values as well. In my groups experiment, we had very inaccurate data. Our electric potential reached over 20V, and never went down to 0V. The electric potential was supposed to be 20V at the middle, and decrease to 0V in concentric circles. Because of this discrepancy, we used results from previous years to conduct our analysis. To improve the lab in the future, we would need a more accurate reading of voltage and a mechanical method of measuring each point.