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Published byTamsyn Johns Modified over 9 years ago
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The forces between electrical charges have an electrical potential energy associated with this force. The total ME = KE + gravitational PE + elastic PE + electric PE.
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If a positive charge is moved in a uniform electric field in the same direction as the field, there is a change (decrease) in the electric potential energy of that charge. ΔPE electric = -qEΔd
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It is the difference in potential that is important. If we set the initial d to be zero, then: PE electric = -qEd This is only true for a uniform field.
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“d” is the magnitude of displacement in the direction of the electric field. Perpendicular motion does not change the PE.
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If there are two charges, another equation is needed. PE electric = kq 1 q 2 /r The reference point is infinity. The ΔPEelectric is + for like charges and - for unlike charges.
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What is the electric potential energy between two electrons that are two meters apart?
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The electrical potential energy associated with an electron and proton is -4.35 x 10 -18 J. What is the distance between these two charges?
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PE electric depends on the charge. A more practical concept is electric potential: PE electric /q = V.
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Electric potential is independent of charge. The reference point for electric potential is arbitrary, only the difference in potential is important. Therefore: ΔV = ΔPE electric /q The unit is the volt, which is equal to one joule per coulomb.
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As a one coulomb charge moves through a potential difference of one volt it gains (or loses) one joule of energy.
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Remember: PE electric = -qEd and ΔV = ΔPE electric /q. So: ΔV = Δ(-qEd/q) or ΔV = -ΔEd
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Voltage difference between a point at infinity and a point near a point charge: ΔV = kq/r
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These potentials are scalars, not vectors; there is no direction involved.
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A 5.0 C point charge is at the origin, and a point charge of -2.0 C is on the x-axis at (3.0m,0.0m). Find the total potential difference resulting from these charges between a point with coordinates (0.0m, 4.0m) and a point infinitely far away.
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A battery does work to move a charge. As a charge moves through a 12V battery its potential is raised by 12V. If it is a 1 coulomb charge its energy is raised by 12 joules.
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