course phy202 R{˝\assignment #004
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17:11:36 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 --> The formula is V= K*Q/r confidence assessment: 2
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17:17:30 ** 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 --> I gave the formula for the potential at a position due to a single point charge. what I should have been thinking is calculating the work to move the charge through the displacement. self critique assessment: 2
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17:19:53 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 --> Vba= -E*d where E is a uniform electric field and d is the distance between the points. confidence assessment: 2
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17:20:16 ** 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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17:25:10 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 --> E = - Vab/d where Vab is the potential difference (voltage) and d is the distance If we're given the charge and the amount of work done then we can easily calculate distance since W / F=d confidence assessment: 2
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17:25:36 ** 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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17:31:15 In your own words explain the meaning of voltage.
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RESPONSE --> I'll tell you what the book says, but then I'll tell you what my gut says. Voltage is a measure of the amount of potential electrical energy existing between the charges and it's measured in Joules/Coulomb or, in other words, energy/charge. My father always told me that if electricity were water and electric lines were a hose, the voltage is analagous to the water pressure while current (amps) are like the size of the stream. Is this right? confidence assessment: 2
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17:31:56 ** Voltage is the work done per unit of charge in moving charge from one point to another. **
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RESPONSE --> Or in other words the strength of the field?
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