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184_notes:examples:week6_drift_speed [2018/02/03 22:23] – tallpaul | 184_notes:examples:week6_drift_speed [2021/06/08 00:49] (current) – schram45 | ||
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=====Example: | =====Example: | ||
Suppose you have a two wires. Each has a current of $5 \text{ A}$. One is made of copper (Cu) and has radius $0.5 \text{ mm}$. The other is made of zinc (Zn) and has radius $0.1 \text{ mm}$. What are the drift speeds of electrons in each wire? You may want to consult the table below. | Suppose you have a two wires. Each has a current of $5 \text{ A}$. One is made of copper (Cu) and has radius $0.5 \text{ mm}$. The other is made of zinc (Zn) and has radius $0.1 \text{ mm}$. What are the drift speeds of electrons in each wire? You may want to consult the table below. | ||
- | {{ 184_notes: | + | [{{ 184_notes: |
===Facts=== | ===Facts=== | ||
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===Approximations & Assumptions=== | ===Approximations & Assumptions=== | ||
- | * The wires have circular cross-sections. | + | * The wires have circular cross-sections. This is typical of real wires and allows us to use the diameter of the wire to calculate the area properly. |
* Using the [[184_notes: | * Using the [[184_notes: | ||
===Representations=== | ===Representations=== | ||
* We represent electron current as $i=nAv_{avg}$. | * We represent electron current as $i=nAv_{avg}$. | ||
- | * We represent current as $I=|q|i$. Current is charge per second. Electron current is electrons per second. We multiply by $q$ (the electron charge) to get charge per second. | + | * We represent current as $I=|q|i$. Current is charge per second. Electron current is electrons per second. We multiply by $q$ (the electron charge) to get charge per second. |
- | * | + | |
====Solution==== | ====Solution==== | ||
We can use the [[184_notes: | We can use the [[184_notes: | ||
- | There is a lot going on in this problem, so let's make a plan. | + | There are a lot of variables |
<WRAP TIP> | <WRAP TIP> | ||
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\end{align*} | \end{align*} | ||
- | Notice that this is actually really slow! Depending on the material, the electron only travels somewhere between 1 mm - 1 cm per second. | + | Notice that this is actually really slow! Depending on the material, the electron only travels somewhere between 1 mm - 1 cm per second |