Understanding the Negative Power Delivered in Circuits

[Mdhiggenz]

Homework Statement

Why is it when referring to the power delivered through a circuit the value is negative, and the power absorbed would be positive?

Logically it doesn't make sense to me that negative power value is being delivered through out the circuit.

Thanks

Higgenz

Homework Equations

The Attempt at a Solution

 

[CherryTrooper]

Because when the power is being delivered, its being "taken away" from the circuit. When it's being absorbed, it's "gaining" power, thus positive.

P= V x I, so if you think about it the electric potential is positive, and the current is positive. It's converting, or charging or something. When it's releasing (or delivering) power, like a battery would do to an associated item, the power in the battery's circuit would be negative (because the current is flowing out, and thus negative)

 

[Mdhiggenz]

awesome explanation thanks!

 

[milesyoung]

Whether a positive number for power means the element is "producing" or "consuming" power depends on the sign convention used.

For the passive sign convention, positive power means the circuit is consuming power. For the active sign convention, positive power means the circuit is producing power:
http://en.wikipedia.org/wiki/Passive_sign_convention#Sign_conventions