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phys: basic current stuffs

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eggy 2021-01-25 17:59:10 -05:00
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@ -868,7 +868,7 @@ $$\lambda_n=\frac{n}{4}L$$
A **charge** is a scalar that allows a mass to experience force from an electromagnetic field, and it may only be positive or negative. It is both **quantised** — the smallest charge possible is the one on a single proton/electron and all charges are multiples of that value — and **conserved** in a closed system. A **charge** is a scalar that allows a mass to experience force from an electromagnetic field, and it may only be positive or negative. It is both **quantised** — the smallest charge possible is the one on a single proton/electron and all charges are multiples of that value — and **conserved** in a closed system.
Charges are expressed in **Coulombs** ($\text{C}$) with the symbol $q$. One electron has a charge of $1.60×10^{-19}\text{ C}$. Charges are expressed in **Coulombs** ($\text{C}$) with the symbol $q$. One electron has a charge of $-1.60×10^{-19}\text{ C}$.
Similar to gravitation, the forces between charges is proportional to their charges and inversely proportional to the square of the distance between them. Similar to gravitation, the forces between charges is proportional to their charges and inversely proportional to the square of the distance between them.
$$F_E \propto q_1q_2 \propto \frac{1}{r^2}$$ $$F_E \propto q_1q_2 \propto \frac{1}{r^2}$$
@ -930,6 +930,24 @@ where any deltas refer to differences between the two plates.
As the electric field strength is constant, the equipotential lines in the field are also evenly distributed. As the electric field strength is constant, the equipotential lines in the field are also evenly distributed.
## 5.2 - Heating effect of electric currents
!!! definition
A **charge carrier** is any mass that enables charges to be moved over a potential difference.
Electric currents ($I$) are the flow of electrons due to a potential difference between both ends of a conductor. They are measured in **amperes** ($\text{A}$) which represent coulombs per second ($1\text{ A}=\frac{1\text{ C}}{1\text{ s}}$).
$$I=\frac{q}{t}$$
The **drift velocity** is the average velocity of electrons in a given volume.
<img src="/resources/images/drift-velocity.png" width=700>(Source: Kognity)</img>
As such, where $I$ is the current, $n$ is the number of electrons, $A$ is the cross-sectional area of the conductor, $q$ is the charge of one electron, and $v$ is the electron drift velocity:
$$I=nAvq$$
$$\Delta Q = nAv\Delta tq$$
In an electric circuit, electrons flow from the negative terminal to the positive terminal — however historically current was described as from the positive to the negative terminal and so that is known as **conventional current**, opposite the direction of electron flow.
## 6.1 - Circular motion ## 6.1 - Circular motion
Circular motion is any motion along a circular path. The instantaneous velocity of an object in circular motion at any point is always tangent to its point on the circle, so the difference between any two velocities ($\Delta \vec{v}$) is radial (lies along the radius). Circular motion is any motion along a circular path. The instantaneous velocity of an object in circular motion at any point is always tangent to its point on the circle, so the difference between any two velocities ($\Delta \vec{v}$) is radial (lies along the radius).