What is the potential difference across the parallel resistors in a circuit?

[Drizzy]

Homework Statement

What is the potential in the batteries "negative part"?
http://imgur.com/7nuxgC3

Homework Equations

3. The Attempt at a Solution [/B]
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

 

[berkeman]

Homework Statement

What is the potential in the batteries "negative part"?
http://imgur.com/7nuxgC3

Homework Equations

3. The Attempt at a Solution [/B]
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

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.

 

[Drizzy]

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

 

[berkeman]

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

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?

 

[Drizzy]

yes! thank you :)