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rcmango
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Homework Statement
a large positive charge +Q fixed at some location in otherwise empty space, far from all other charges. A positive test charge of smaller magnitude +q is launched directly towards the fixed charge. Of course, as the test charge gets closer, the repulsive force exerted on it by the fixed charge slows it down. Your job is to explain why the test charge slows down, but in terms of electric potential and EPE, rather than in terms of fields or forces.
explain how the electrical potential encountered by the test charge changes as it gets closer to the fixed charge, and why.
explain how the EPE of the test charge changes as it gets closer to the fixed charge, and why.
Homework Equations
The Attempt at a Solution
The EPE difference between q and Q does not change, it says the same proven using this formula k(Q-q)/r, the EPE is always increasing as the test charge approaches the fixed charge, q EPE is increasing and Q's EPE is increasing.
The work done by the net E field in moving a test charge a distance defines EPE. So's as q moves closer to Q the fixed charge, q gains PE, in turn q also gains EPE. The voltage is increasing.
The voltage from the equipotential fields are not the same due to the fixed charge at the moving charge, or at the moving charge due to the fixed charge. However, the difference due to both charges are the same. ( V = k(Q-q)/r )
The particle is slowing down and eventually stops when the potentials are equal amounts.
below, is a response to my paragraph, I am really having a hard time addressing what is going on using PE and EPE, can someone stick with me on this and guide me through writing a short paragraph explaining what is needed to answer the two sentences above. Thanks alot.
The expression k(Q-q)/r doesn't apply to this situation. The test charge q is simply experiencing the potential created by the fixed charge Q. You say that q gains PE and therefore also EPE, but the only kind of PE that q gains is EPE. Start with what happens to the potential as q gets closer to Q, then deduce what happens to its EPE, and then use the energy conservation principle to explain why the charge slows down.