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| 184_notes:batteries [2018/06/11 19:05] – [Symbol for a Battery] curdemma | 184_notes:batteries [2020/08/23 19:19] – dmcpadden |
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| Part of Section 18.4 in Matter and Interactions (4th edition) | Part of Section 18.4 in Matter and Interactions (4th edition) |
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| [[184_notes:q_in_wires|Next Page: Surface Charges around Circuits]] | /*[[184_notes:q_in_wires|Next Page: Surface Charges around Circuits]] |
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| [[184_notes:motiv_movingq|Previous Page: Motivation for Moving Charges]] | [[184_notes:motiv_movingq|Previous Page: Motivation for Moving Charges]]*/ |
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| ===== Batteries ===== | ===== Batteries ===== |
| While a pair of charged plates is easy to think about on a general level, it becomes surprisingly complicated to model at a microscopic level. As electrons move from one plate to the other, the amount of excess charge on each plate decreases, which means that over time, the "driving force" that is pushing the electrons through the wire is also decreasing. Thus, the flow of electrons (which we will eventually define as the **electron current**) is always changing - starting as a large flow of electrons from one plate to the other and decreasing until the plates are neutral and there is no electron flow between them. | While a pair of charged plates is easy to think about on a general level, it becomes surprisingly complicated to model at a microscopic level. As electrons move from one plate to the other, the amount of excess charge on each plate decreases, which means that over time, the "driving force" that is pushing the electrons through the wire is also decreasing. Thus, the flow of electrons (which we will eventually define as the [[184_notes:defining_current|electron current]]) is always changing - starting as a large flow of electrons from one plate to the other and decreasing until the plates are neutral and there is no electron flow between them. |
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| Rather than dealing with a constantly changing electron current, we are going to start by thinking about a simpler model - one where we //__assume the electron current is constant__// from a battery. (We will return to this idea of charged plates and a changing electron current next week). | Rather than dealing with a constantly changing electron current, we are going to start by thinking about a simpler model - one where we //__assume the electron current is constant__// from a battery. (We will return to this idea of charged plates and a changing electron current next week). |
| Oftentimes in circuits, we are less concerned with how the electrons in circuits are produced and are more concerned with what happens to the charges after they are produced. This means we will generally simplify our model of the battery to what we call a "mechanical model" of the battery. In this model, the battery consists of two charged plates, one that is positive and one that is negative, with a conveyor belt that pulls the electrons from the positive plate to the negative plate. In this model, //the conveyor belt represents the chemical reaction in the battery that maintains the separation of charge//. | Oftentimes in circuits, we are less concerned with how the electrons in circuits are produced and are more concerned with what happens to the charges after they are produced. This means we will generally simplify our model of the battery to what we call a "mechanical model" of the battery. In this model, the battery consists of two charged plates, one that is positive and one that is negative, with a conveyor belt that pulls the electrons from the positive plate to the negative plate. In this model, //the conveyor belt represents the chemical reaction in the battery that maintains the separation of charge//. |
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| When the positive and negative plates of the battery are connected by a conducting wire, the excess electrons on the negative plate will travel through the wire toward the positive plate. When they arrive at the positive plate, the "conveyor belt" will return the negative charges to the negative plate, keeping a constant amount of negative charge and a constant amount of positive charge on the plates. **The primary consequence of this is that there will be a constant electron current in the wire coming from the battery**. Using this model of the battery, we can think about what is happening in circuit when the flow of electrons is constant; we will often call this "the steady state of the circuit" or the __//steady state assumption//__. | When the positive and negative plates of the battery are connected by a conducting wire, the excess electrons on the negative plate will travel through the wire toward the positive plate. When they arrive at the positive plate, the "conveyor belt" will return the negative charges to the negative plate, keeping a constant amount of negative charge and a constant amount of positive charge on the plates. **The primary consequence of this is that there will be a constant electron current in the wire**. Using this model of the battery, we can think about what is happening in circuit when the flow of electrons is constant; we will often call this "the steady state of the circuit" or the __//steady state assumption//__. |
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| ==== Symbol for a Battery ==== | ==== Symbol for a Battery ==== |