add electrical fundamentals

uni/mmme/2xxx/2051_electromechanical_devices/fundamentals.md

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+---
+author: Akbar Rahman
+date: \today
+title: MMME2051 // Electrical Engineering Fundamentals
+tags: [ mmme2051 ]
+uuid: 412c8cb8-ec0c-4d6f-b899-f1296f4fc639
+---
+
+# Across Variable vs Through Variable
+
+Across variables:
+
+- Appears across two terminal of an element
+- Measured relative to a reference point
+- e.g. voltage
+
+Through variables:
+
+- Value is same at both terminals of an element
+- e.g. current
+
+# Ohm's Law
+
+For all components that follow Ohm's law:
+
+$$V = IR$$
+
+where $V$ is voltage across a component, $I$ is current through it, and $R$ is resistance of the component.
+
+# Impedance vs Resistance
+
+- Impedance is used when there are energy storage elements to a component.
+- Resistance, a special case of impedance, can be used when there is no storage element
+
+# Kirchhoff's Laws
+
+## Current
+
+The sum of current entering a node is 0
+
+$$\sum_n I_n = 0$$
+
+## Voltage
+
+The sum of voltage around a closed loop is 0
+
+$$\sum_n V_n = 0$$
+
+# Energy Storing Elements --- Reactive Elements
+
+When you apply a voltage to a reactive element, the reactive element will start storing energy.
+When the voltage is removed, it will push current until all energy is dissipated.
+
+There are two types of Reactive Elements
+
+## Inductors
+
+A coil of wire wound around a magnetic core, such as iron.
+
+They have a property, inductance, with SI unit henry and symbol H.
+
+For an inductor:
+
+$$V = L\frac{\mathrm{d}I}{\mathrm{d}t}$$
+
+where $L$ is the inductance of the coil.
+
+Energy is stored in the magnetic flux around the coil.
+
+This creates the behaviour of trying to minimize change in current.
+
+If you remove the voltage source and open the circuit, the inductor would have a voltage approaching
+infinity, causing problems if the energy stored in the inductor is high enough.
+
+## Capacitor
+
+For a capacitor:
+
+$$I = C\frac{\mathrm{d}V}{\mathrm{d}t}$$
+
+Energy is stored in the form of electrostatic attraction in the adjacent plates.
+
+Capacitors try to minimize changes in voltage.
+
+If a capacitor is shorted, the current through the connecting wires will be extremely high, causing
+the wires to heat up.