Unit
The unit of capacitance C C C F F F microfarad, abbreviated as μ F \mu F μ F 1 μ F = = 1 0 − 6 F 1\mu F == 10^{-6}F 1 μ F == 1 0 − 6 F
u = 2 U sin ( w t + ψ u ) i = C d u d t = C ⋅ u ′ = 2 w C U cos ( w t + ψ u ) = 2 w C U sin ( w t + ψ u + π 2 ) i = 2 I sin ( w t + ψ u + π 2 ) = 2 I sin ( w t + ψ i ) \begin{align*}
u &= \sqrt{2} U \sin(wt + \psi_u)
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i = C\frac{du}{dt} = C \cdot u^\prime &= \sqrt{2} wCU \cos(wt + \psi_u) = \sqrt{2}wCU \sin(wt + \psi_u + \frac{\pi}{2})
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i &= \sqrt{2} I \sin(wt + \psi_u + \frac{\pi}{2}) = \sqrt{2} I \sin(wt + \psi_i)
\end{align*} u i = C d t d u = C ⋅ u ′ i = 2 U sin ( wt + ψ u ) = 2 wC U cos ( wt + ψ u ) = 2 wC U sin ( wt + ψ u + 2 π ) = 2 I sin ( wt + ψ u + 2 π ) = 2 I sin ( wt + ψ i ) So here we can see:
I = w C U ψ i = ψ u + π 2 \begin{align*}
I &= wCU
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\psi_i &= \psi_u + \frac{\pi}{2}
\end{align*} I ψ i = wC U = ψ u + 2 π 在电感元件中，电流的相位 ψ i \psi_i ψ i ψ u \psi_u ψ u 90 ∘ {90}^\circ 90 ∘
Actually, 1 w C \frac{1}{wC} wC 1 R R R I = U R I = \frac{U}{R} I = R U
So we call 1 w C \frac{1}{wC} wC 1 capacitive reactance (容抗). Ω \Omega Ω