This is probably a stupid question, and I realized the answer before, and I know my professor explained this in class, but why does voltage lead current for inductors and current lead voltage for capacitors. I don't want a physical explaination but a mathematical one. I am looking at my circuits notes and my professor states that it is obvious from the following equations that this is true.//<![CDATA[ aax_getad_mpb({ "slot_uuid":"f485bc30-20f5-4c34-b261-5f2d6f6142cb" }); //]]>

V = j(omega)LI and I = j(omega)CV, where omega is frequency and I and V are the current and voltage phasors.

I know this is stupid because I was able to answer this question myself fairly easily just by looking at the equations, but now I look at them again and cannot answer this question for the life of me. SOMEONE HELP ME!! :(

If I can't figure this out on my own then I will ask my professor tomorrow, but I'd rather not ask such a question since he states that it is obvious in his lecture notes.

Thanks a lot.

edit: I suppose if you plug the phasors into the above equations and then convert them from exponential form to trigonometric form using euler's identity the sine expression becomes the real part (formerly the imaginary part) and then the cosine expression becomes the imaginary part (formerly the real part). Making the sine expression the real part would make the wave 90 degrees out of phase. Is this correct? I remember realizing the answer to this question before and my reasoning seemed much simpler.

**Physics Forums - The Fusion of Science and Community**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# ELI the ICE man

Have something to add?

**Physics Forums - The Fusion of Science and Community**