EMI and Alternating Currents — Easy Practice (Set 2)

Quick Recap — Alternating Current

• AC: $I = I_0\sin\omega t$; rms values $I_{rms} = \dfrac{I_0}{\sqrt2}$ and $V_{rms} = \dfrac{V_0}{\sqrt2}$.
• Reactance: inductive $X_L = \omega L$; capacitive $X_C = \dfrac{1}{\omega C}$.
• Impedance: $Z = \sqrt{R^2 + (X_L - X_C)^2}$; the current lags the voltage in an inductor and leads it in a capacitor.
• Resonance: $X_L = X_C$, so $Z = R$ (minimum), the current is maximum, and $f_0 = \dfrac{1}{2\pi\sqrt{LC}}$.
• Power: $P = V_{rms}I_{rms}\cos\phi$ (power factor $\cos\phi = R/Z$); a transformer obeys $\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}$ and conserves power ideally.