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phasor diagrams

i was just wondering in electricity when asked to find the resultant voltage in a LR or RC circuit how do u know if capactance would be facing down (going down the negative end of the y axis)

i was taught the term CIVIL and how for capacitance the current leads the voltage so it goes up the y axis but some examples i have seen so the opposite. i really need some help with this as i have a exam on friday!

thanks in advance

Reply 1

teachercol

CIVIL works. To prove why it works needs a bit of caclulus.

You draw the reference phasor first. This is the quantity that is the same for all the components. For a series circuit this will be current, then the draw the voltages relative to that. Fora parallel circuit, you draw the voltage first then draw the currents relative to it.

CIVIL helps you remember what goes where.