Homework Help: Potential in a circuit

1. Nov 24, 2015

Drizzy

1. The problem statement, all variables and given/known data
What is the potential in the batteries "negative part"?
http://imgur.com/7nuxgC3
2. Relevant equations
3. The attempt at a solution

I don't know how to think...
My total resistance is:
[(1/50) + (1/75)]^-1 + 10 = 40 ohm
I=V/R = 36/40 = 0.9
The voltage on the 10ohm resistance is 0.9 *10 = 9V
Now I know that the voltage on the parallell resistances is 36-9 = 27v
Now I have to go from ground :

0 - 27 - 9 = -36

But this is wrong... I don't understand why

2. Nov 24, 2015

Staff: Mentor

The question is not worded very well, but I'm guessing they want you to say that there is +9V on the "positive" part of the battery and -27V on the "negative" part.

3. Nov 24, 2015

Drizzy

exactly but how do you know that it is 9 and -27?

4. Nov 24, 2015

Staff: Mentor

You correctly calculated the voltage across the 10 Ohm resistor as 9V. Since the right side of that resistor is grounded, the left side of the 10 Ohm resistor will be at +9V. Same deal with the right two resistors. Makes sense?

5. Nov 24, 2015

Drizzy

yes! thank you :)