Is there an equationg for for finding how much current is drawn from a power source?

I know how to find total resistance etc so thats fine, but is it to do with conductance etc?
P = IV i think. so if you know the voltage, you can find the current drawn. also, V=IR will help as well i think. but i dunno anything about conductance
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Damn...I know this one. Current would be the amp...or watts. Help me help you....are looking for volts, watts, amps, or what?
Well i've got the p.d of the power supply : 6volts and theres a 5 ohm resistor going into a parralel set up of 4 and 6 ohms which ill get back to you in a second about how many ohms that is in total

EDIT: I think its just

R= 0.81

To find I use v= I R which is the same as I= 6/7.4 = 0.81C

P= 0.81 x 6 = 4.86 W
Last edited by philipisabeast at Oct 8, 2007,