course Phy 122 ?x?????v?????assignment #004004.
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21:34:13 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 definition of potential difference is ""the work done on a charge by an electric force."" We know that change in potential energy is equal and opposite to the work done when a charge is moved from one point to another. Work can be found by multiplying average force by the distance from one point to the other. -`dPE = W = Fave x `ds Average force is found by simply averaging the forces found at each point charge. Displacement can be found by first finding the x and y components of the electric field and using the Pythagorean Theorem. confidence assessment: 2
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21:35:28 ** 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 --> My explanation is basically the same as the solution. I did not mention, however, that an accurate way to measure large displacements is the split them up into smaller intervals. self critique assessment: 2
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21:49:36 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 --> Potential difference, or work per unit charge, can be found by either `dV = W = Fave*`ds or by finding the electric field by F/q and multiplying by the change in displacement, `dV = E*`dr = (Fave/q)(`dr). confidence assessment: 3
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** 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 --> My answer is stated slightly differently, but I believe it means the same thing. self critique assessment: 2
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21:52:42 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 --> If you are given the points, you can find the displacement. Therefore, you can use work and displacement to calculate the average force. Fave = `dW/`ds. After finding the force, you can use the magnitude of the charge at a point to find the electric field: E = Fave/q confidence assessment: 3
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21:53:56 ** 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 --> I did not mention the alternative approach, but I completely understand that finding the potential difference is also a way to get to the electric field: `dV = `dW/q E = `dV/`ds self critique assessment: 2
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21:55:05 In your own words explain the meaning of voltage.
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RESPONSE --> Voltage is a term to describe potential energy. Voltage is a measure of work per unit charge between points, measured in Joules per Coulomb. confidence assessment: 3
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21:55:15 ** Voltage is the work done per unit of charge in moving charge from one point to another. **
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RESPONSE --> I understand. self critique assessment: 3
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