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Formula Sheets / Physics

Chapter 24

Alternating Current

Revise with flashcards Download this chapter (PDF) All Physics formulas (PDF)

AC circuits and impedance Resonance, power and power factor Transformers and LC oscillations

AC circuits and impedance

RMS values
$I_{rms} = \frac{I _{0}}{2},$ $V_{rms} = \frac{V _{0}}{2};$ average over half cycle $\frac{2 I _{0}}{π}$
Reactances
$X_{L} = ω L,$ $X_{C} = \frac{1}{ω C}$
Series LCR
$Z = R^{2} + (X_{L} - X_{C})^{2},$ $tan ϕ = \frac{X _{L} - X _{C}}{R}$

Resonance, power and power factor

Resonance
$ω_{0} = \frac{1}{L C},$ $Z = R,$ $Q = \frac{ω _{0} L}{R} = \frac{1}{R} \frac{L}{C}$
Power
$P = V_{rms} I_{rms} cos ϕ,$ $cos ϕ = \frac{R}{Z}$
Bandwidth
$Δ ω = \frac{R}{L}$

Transformers and LC oscillations

Transformer
$\frac{V _{s}}{V _{p}} = \frac{N _{s}}{N _{p}} = \frac{I _{p}}{I _{s}}$ (ideal)
LC oscillations
$q = q_{0} cos ω t,$ $ω = \frac{1}{L C},$ $\frac{q _{0}^{2}}{2 C} = \frac{1}{2} L I_{0}^{2}$

Electromagnetic Induction Electromagnetic Waves