And who said mains voltage it 240V LoL

[#1]

Open and closed circuits, a closed circuit will have voltage and current an open circuit will have voltage but no current. If a light switch is off it's an open circuit with no current flowing but voltage on one of the switch poles. The v=ir formula are only for closed circuits.

[#2]

Actually the proper term to use is Electromotive Force. This describe the voltage applied at the beginning of the circuit as 0 voltage can be measured when current is flowing i.e. on the 0v return path.

[#3]

and dont forget the square root of minus 1 = J

[#4]

I thought it was i

[#5]

Well it was a long time ago I did it, just wanted to see if you were in Phase
But according to http://en.wikipedia.org/wiki/Imaginary_unit it can be either, so perhaps I was right when I went to college?

[#6]

from that link, it depends who you are as to what it is - I'm a mathematician by Uni degree course, so I'd go for i, yet physicists would probably go for the j to avoid confusion with current (i).

[#7]

Which raises the question - why is "I" used for current?
I could understand (A)mpere or (C)urrent or (C)harge - but what does I stand for?

[#8]

This may explain http://en.wikipedia.org/wiki/SI_electromagnetism_units C can't be used as this is for Charge which is Coulombs.
(A) can't be used as this is already used in current formula to represent area, I=nAvQ