Physics: Week 29

This week in the Ron Paul Curriculum physics course covered the basics and introduction to ac circuit analysis.

Basics of AC current

AC through a resistor:

The current and voltage is always in phase and Ohms law applies.  The energy is transferred into heat and lost in the environment. 

Inductor in series:

By kerchiefs law, voltage must  sum to zero. 

Current lags the voltage by 90 degrees of the voltage leads the current.

Inductive reactance:

An inductor impedes the flow of current, it does not want it to change.  The current flow is directly proportional to the applied voltage at a given frequency such that we can have an equation similar to Ohm’s law

Capacitors in series:

Electrical engird is put into the electric field within the capacitor, but then comes back into the circuit.  No net energy is lost.

With a DC current there is no current flow like in AC current.

Capacitive reactance:

It depends on the capacitance of the current and the frequency of the applied current. (equation) 

ELI the ICE man

Inductor = Voltage leads Current, Capacitor = Current leads Voltage

E= voltage

L = inductance

I = current

C = capacitance 

LRC diagram:

At any instant in time, Kirchoff’s law will hold so that V = VR + VC + VL
At any given time the current is the same everywhere in the circuit because the charge does not pile up in the wires.
The best way to analyze the LRC diagram is with a phasor diagram:

Total impedance:

Power and power factor:

Power is only dissipated through the resistor, therefore we have to look at the voltage and current through it.

Resonant frequency:

At a certain frequency the current is at maximum flow. 

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