- #1
DaVinci
- 75
- 0
I tried this thread in the Electrical Engineering area and nothing. So, hopefully someone reading this can explain this problem I am having.
We know that current in one direction is equal to its negative in the opposite direction. We also know P=IV for power. We also know that when current is going from + to -, P absorbed is +VI and P delivered = -VI. When you have current going from - to +, Pabs = -VI and Pdel = +VI.
So, you have -3A going from + to - through an element. There is 6V across that element. P=IV = (-3)(6) = -18W. Since the answer is - and current going from + to -, Pdel = -VI so it is -18W delivered. (Is my train of thought the correct way to view this?)
Now, imagine the same problem. You would have 3A going from - to +. So, P=IV=(3)(6) = 18W. Since current going from - to +, Pdel = +VI, so you have 18W delivered.
The signs are different! The book says the answer is P delivered = -18W. In both cases I found that the power is delivered. But the sign is off in the second example leading to an incorrect answer...
Anyone know what the heck is going on?
We know that current in one direction is equal to its negative in the opposite direction. We also know P=IV for power. We also know that when current is going from + to -, P absorbed is +VI and P delivered = -VI. When you have current going from - to +, Pabs = -VI and Pdel = +VI.
So, you have -3A going from + to - through an element. There is 6V across that element. P=IV = (-3)(6) = -18W. Since the answer is - and current going from + to -, Pdel = -VI so it is -18W delivered. (Is my train of thought the correct way to view this?)
Now, imagine the same problem. You would have 3A going from - to +. So, P=IV=(3)(6) = 18W. Since current going from - to +, Pdel = +VI, so you have 18W delivered.
The signs are different! The book says the answer is P delivered = -18W. In both cases I found that the power is delivered. But the sign is off in the second example leading to an incorrect answer...
Anyone know what the heck is going on?