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184_notes:batteries [2017/09/20 18:36] – dmcpadden | 184_notes:batteries [2020/08/20 16:33] – dmcpadden | ||
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+ | Part of Section 18.4 in Matter and Interactions (4th edition) | ||
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===== Batteries ===== | ===== Batteries ===== | ||
- | A battery is a source | + | While a pair of charged plates is easy to think about on a general level, it becomes surprisingly complicated |
+ | 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__// | ||
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+ | A battery is a source of electric energy - and electron current - that we use on an everyday basis. Your cell phone, car, calculator, and many other devices all rely on batteries to function. For our purposes, we are particularly interested in batteries because over a short amount of time, a battery can provide a constant source of electrons, that we can use to light a lightbulb, power a calculator, or any number of other electrical devices. These notes will discuss briefly the chemical model of a battery (which is how a AA battery works for example), then introduce the mechanical model of a battery, which helps simplify the function of a battery in a circuit. | ||
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+ | {{youtube> | ||
==== Chemical Model of a Battery ==== | ==== Chemical Model of a Battery ==== | ||
- | {{ 184_notes: | + | [{{ 184_notes: |
- | A battery is ultimately a chemical separation of charge. The battery consists of two metal plates placed in a salt solution: one metal produces excess negative charges when reacting with the salt solution (leaving the salt solution | + | A battery is ultimately a chemical separation of charge. The battery consists of two metal plates placed in a salt solution: one metal produces excess negative charges when reacting with the salt solution (leaving the metal positive) and one metal produces negative charge in the salt solution leaving the metal positive. Chemically this is often referred to as a [[https:// |
This is of course a very rough explanation of a chemical battery. Many physicists and chemists are [[https:// | This is of course a very rough explanation of a chemical battery. Many physicists and chemists are [[https:// | ||
==== Mechanical Model of a Battery ==== | ==== Mechanical Model of a Battery ==== | ||
- | {{ 184_notes: | + | [{{ 184_notes: |
- | 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 " | + | 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 " |
- | 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 " | + | 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 " |
==== Symbol for a Battery ==== | ==== Symbol for a Battery ==== | ||
- | {{ 184_notes: | + | [{{ 184_notes: |
+ | {{184_notes: | ||
When describing circuits, we will often draw out a symbolic representation (called a circuit diagram) of the circuit elements that we can use to think about what is happening to the charges in the circuit. When representing a battery, we will either draw out the mechanical model of the battery (including the positive plate, negative plate, and conveyor belt) as shown above, or we will draw out a simplified version of the battery including a short line for the negative plate and a long line for the positive plate (where the steady state is assumed without explicitly drawing the conveyor belt). You may also see a physical drawing of a battery drawn out (particularly in textbooks) with the positive and negative sides of the battery explicitly labeled. Any of these representations of a battery will work. | When describing circuits, we will often draw out a symbolic representation (called a circuit diagram) of the circuit elements that we can use to think about what is happening to the charges in the circuit. When representing a battery, we will either draw out the mechanical model of the battery (including the positive plate, negative plate, and conveyor belt) as shown above, or we will draw out a simplified version of the battery including a short line for the negative plate and a long line for the positive plate (where the steady state is assumed without explicitly drawing the conveyor belt). You may also see a physical drawing of a battery drawn out (particularly in textbooks) with the positive and negative sides of the battery explicitly labeled. Any of these representations of a battery will work. | ||