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I know that this subject is confusing on first read with many equations. The basic principles are not that bad but the subject gets very equation busy very quickly.

Here is our formula sheet on AC circuits (top right corner of this image is for DC RL and LC without a source).

Let us practice what we have learned with a few more examples.

Here is a trick to remember whether the inductor/capacitor lags or lead. "ELI the ICE man". Emf leads the current (leads as in comes first) for an inductor (ELI) while the current leads the emf for a capacitor (ICE).

Problem Solving

Q1: The small transformers that power many consumer products produce a 12.0 V rms, 60 Hz emf. Design a circuit using resistors and capacitors that uses the transformer voltage as an input and produces a 6.0 V rms output that leads the input voltage by 45°.

Q2: The figure below shows voltage and current graphs for a series RLC circuit.

a) What is the resistance R?

b) If L = 200 µH, what is the resonance frequency in Hz?

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