# Phases of current and voltage

Why $$u(t)$$ and $$i(t)$$ are in the same phase in a resistor, but in a condensator $$i(t)$$ is ahead of $$u(t)$$ by $$\pi/2$$, and vice versa in a coil?

Note: I need physical explanation, like main reason of this act. No need for mathematical reasons like

$$i(t) = C \frac{du}{dt}$$ When $$u(t)=U\sqrt{2}\sin\omega t$$, then $$i(t)=C\omega\cdot U\sqrt{2}\sin(\omega t+\pi/2)$$.

This case is for condensator as you know.

• Welcome New contributor Physics009! What do you mean by 'physical explanation'? What research effort have you already done to find such an explanation? Should the reader assume that you have done zero research on the physical basis of resistance and capacitance? If you have done some research, it would be helpful if you share that and explain what remains unclear. You might find the following link helpul: How do I ask a good question? - "Have you thoroughly searched for an answer before asking your question?" – Alfred Centauri Sep 15 '19 at 12:56
• Do you understand why the capacitor is described by $i(t)=c\frac{du}{dt}$? Because once you understand why the equation describes the behavior of the capacitor in time domain, you understand why the capacitor voltage lags current for AC excitation. – The Photon Sep 15 '19 at 15:55