Potential Change in a Circuit Diagram

AI Thread Summary
The discussion revolves around determining the potential at point Q given that the potential at point P is 400 V. The user applied Ohm's Law and the principle that the sum of potential changes in a circuit loop must equal zero. They initially calculated the current to be 20 A and then used this value to find the potential at point Q, arriving at 290 V. There is some confusion regarding the relevance of the 400 V potential in their calculations. The solution provided appears to be correct based on the user's calculations.
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[SOLVED] Potential Change in a Circuit Diagram

Homework Statement


http://personalpages.tds.net/~locowise/test/28_29.gif

If the potential at point P is 400 V, what is the potential at point Q?


Homework Equations


Ohm's Law: deltaV=iR
Probably the fact that the sum of changes in potential in a loop of any circuit must be zero.

The Attempt at a Solution


Not real sure on this problem. I tried this:
150V - 2.0i - 3.0i - 50V = 0V and found i to be 20A.

I'm kind of puzzled and can't seem to relate the material in the textbook to this problem. Where does the 400V potential come into play? Thanks for your help!
 
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I'm still not really sure this is the proper way to approach the problem but apparently the solution is correct. Here's what I did:

Used 20A from above.

400V - 50V - 3.0ohms * 20A = 290V
 

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