Ast 4

course Phy 202

It would really help if the figures in the problem sets worked. All of the links are bad.

I just checked Introductory Problem Set 1 and found one bad link, to the figure for Problem 4. I'll try to restore that link tomorrow.

All other links appear to be working, and I haven't had anyone else mention a problem with these links.

If you find a bad link let me know as specifically as you can where it is--on what problem, in what problem set.

~ݵ·ñ׬ԑòóèáçž«þÅÅÚassignment #004

Your work has been received. Please scroll through the document to see any inserted notes (inserted at the appropriate place in the document, in boldface) and a note at the end. The note at the end of the file will confirm that the file has been reviewed; be sure to read that note. If there is no note at the end, notify the instructor through the Submit Work form, and include the date of the posting to your access page.

004.

Physics II

10-24-2007

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02:16:20

Query introductory set #1, 10-17

Explain how to find the potential difference in volts between two given points on the x axis, due to a given charge at the origin.

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RESPONSE -->

Potential differnece is the amount of work in joules per coulomb that a charge moves between two points. To find the work, you multiply the force on the charge by distance the charge moves. So, W = N*m = J and J/C = V. So if you want the potential difference, you find the difference betweens the two voltages at each point.

'dV = V2- V1

confidence assessment: 3

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02:16:33

** Potential difference is the work per Coulomb of charge moved between the two points. To find this work you can multiply the average force on a Coulomb of charge by the displacement from the first point to the second.

You can find an approximate average force by finding the force on a 1 Coulomb test charge at the two points and averaging the two forces. Multiplying this ave force by the displacement gives an approximate potential difference.

Since the force is not a linear function of distance from the given charge, if the ratio of the two distances from the test charge is not small the approximation won't be particularly good. The approximation can be improved to any desired level of accuracy by partitioning the displacement between charges into smaller intervals of displacement and calculating the work done over each. The total work required is found by adding up the contributions from all the subintervals.

University Physics students should understand how this process yields the exact w ""ork, which is the integral of the force function F(x) = k Q / x^2 between the two x values, yielding total work W = k * Q * 1 Coulomb ( 1 / x1 - 1 / x2) and potential difference V = k * Q ( 1 / x1 - 1 / x2). **

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RESPONSE -->

ok

self critique assessment: 3

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02:25:27

Explain how to find the potential difference between two points given the magnitude and direction of the uniform electric field between those points.

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RESPONSE -->

To find the voltage between two points given the magnitude an direction of the electric field, you multiply the electric field by the distance between the points.

V = E * 'dx

Showing units, that's

J/C = N/C * m, which is also

J/C = (N*m)/C

confidence assessment: 3

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02:25:42

** The work per Coulomb done between the two points is equal to the product of the electric field E and the displacement `dr. Thus for constant field E we have V = E * `dr. **

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RESPONSE -->

ok

self critique assessment: 3

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02:35:50

Explain how to find the average electric field between two points given a specific charge and the work done on the charge by the electric field as the charge moves between the points.

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RESPONSE -->

To find the electric field you have to first find the force using the work done over the distance betwee the two points. This force can be found by dividing thw work by the distance. F = W/'ds. Then, to find the electric field, you use the force calculated and the charge given and divide the force by the charge. E = F/Q.

Or since the electric field is also the change in voltage over the change in distance, you can find the electric field by dividing the change in voltage by the change in distance. E= 'dV/'ds. To find the change in voltage, divide the change in work by the charge. 'dV = 'dW/Q.

confidence assessment: 3

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02:35:58

** You get ave force from work and distance: F_ave = `dW / `ds.

You get ave electric field from work and charge: E_ave = F / q.

An alternative:

Find potential difference `dV = `dW / q.

Ave electric field is Eave = `dV / `ds **

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RESPONSE -->

ok

self critique assessment: 3

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02:37:12

In your own words explain the meaning of voltage.

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RESPONSE -->

Voltage is the tha amount of work done per unit charge when moving a charge between two points. V= J/C.

confidence assessment: 3

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02:37:21

** Voltage is the work done per unit of charge in moving charge from one point to another. **

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RESPONSE -->

ok

self critique assessment: 3

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Good work. Let me know if you have questions. &#