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184_notes:q_in_wires [2021/02/18 17:08] – [Simple Circuit] bartonmo | 184_notes:q_in_wires [2021/02/18 21:17] – bartonmo | ||
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We have already talked about how to model a battery as a separation of charges. However, if we connect the two ends of the battery with a conducting wire, what happens to the charge distribution in the wire? Using [[184_notes: | We have already talked about how to model a battery as a separation of charges. However, if we connect the two ends of the battery with a conducting wire, what happens to the charge distribution in the wire? Using [[184_notes: | ||
- | {{youtube> | + | {{youtube> |
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We will start with the simplest circuit possible: a battery connected by a conducting wire (shown to the right). If we //__assume the battery is a mechanical battery__//, | We will start with the simplest circuit possible: a battery connected by a conducting wire (shown to the right). If we //__assume the battery is a mechanical battery__//, | ||
- | If the electrons are moving, there has to be some sort of force that is making those charges move. From what we talked about before, we know we can write this force on the electron in terms of the electron charge and the electric field it is in: | + | If the electrons are moving, there has to be some sort of force that is making those charges move. [[184_notes: |
$$\vec{F}_{e^-}=q_{e^-}\vec{E}$$ | $$\vec{F}_{e^-}=q_{e^-}\vec{E}$$ | ||
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- If the force that pushes the electrons comes from the surface of the wires, then the proximity to the battery doesn' | - If the force that pushes the electrons comes from the surface of the wires, then the proximity to the battery doesn' | ||
- | Thus, surface charges as the model for how charges move through wires is far more consistent with the observations we have in real circuits in everyday life. If you have a very large battery (also called a high voltage power supply) it is actually possible to observe the surface charges on a wire. Here's a video demonstrating | + | Thus, surface charges as the model for how charges move through wires is far more consistent with the observations we have in real circuits in everyday life. If you have a very large battery (also called a high voltage power supply) it is actually possible to observe the surface charges on a wire. |
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+ | {{ youtube> | ||
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+ | In this video, you can see the mechanical effects of surface charge when a piece of foil is held by the positive end, negative end, and neutral center of the wire. On the ends of the wire, the foil is initially attracted, polarized, and then repelled. Since the surface charge at the center of the wire is 0 nothing happens to the foil. A metal pen can also be used to see what kind of charge the foil has picked up based on if it is attracted to or repelled by the pen. | ||
- | {{ youtube> | ||
==== Examples ==== | ==== Examples ==== | ||
[[: | [[: |