STUDY GUIDE 8, SELF TEST 2

© Department of Physics, University of Guelph.

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1. Potential differences between some pairs of points are given below. Calculate the unknown potential differences VCA, VAD, VDB.

Hint: When considering potential differences one may arbitrarily assign any point a potential of zero (rather than "zero at infinity"). E.g., if you set VA = 0, then VB must be +5 V (since VBA = 5 V); continue for values of V at C and D and then determine VCA etc.

2. At a point A near some ions in solution, the potential is 50 V, i.e., VA = 50 V relative to 0 at infinity.
(a) What "electrical work" (i.e., work against the E-field of the ions must you do to move a SO=4 at constant speed (no KE change) from infinity to point A?
(b) What "electrical work" would you have to do to move the SO=4 back from A to infinity?
(c) What is the electrical PE of the SO=4 ion at the point A?
(d) What work would the electric field do on the SO=4 ion if it moves from A to infinity?

3. Referring to Question 2. At a second point B, the potential is VB = -20 V.
(a) What electrical work must you do to move the ion at constant speed from A to B?
(b) What is the change in the SO=4 ion's electrical PE when it goes from A to B?

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