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In capacitive circuit, the voltage and current are out of phase. the current leads the voltage by 90 degrees. this can be explained by these two equations:

$$V = V_{\max} \sin \omega t$$

$$I = I_{\max} \cos \omega t.$$

Now, my question is that what does this statement mean physically that "current leads the voltage by 90 degrees? It is clear mathematically that if $V = 0$ then $I$ is maximum but how do we explain this physically? hope you understood my question

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1 Answer 1

Capacitor charge $q$ is just the accumulation of the current $i$ into the capacitor:

$$ q = \int i \, dt \quad \text{or} \quad i = \frac{dq}{dt} $$

So, starting with an uncharged capacitor, a current $i$ does not instantaneously lead to a charge $q$; instead charge builds up with time, lagging the current. The formulas you quoted are direct consequences of this behavior.

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