Question is, find voltage at point B.
Total voltage 12 V - 9 V = 3 Volts
Total resistance = (47+27+56+20)10^3 = 150000 Ohms
Circuit current = V/R = 3/150000 = 0.00002 Amps

I can go 2 directions:
R2, R1, and 9 V back to ground
OR
R3, R4, 12 V back to ground.

R2+R1 = 74000 Ohms * 0.00002 Amps = 1.48 Volts
R3 + R4 = 76000 Ohms * 0.00002 Amps = 1.52 Volts

9 - 1.48 = 7.52 Volts
12 - 1.52 = 10.48 Volts

From my understanding it should be add voltage drops and then subtract from voltage source. Going both directions does not give same result but it should. Answer should be 10.48 Volts meaning I should do 9+1.48 but why is one side subtract from voltage source and one is add voltage source?

I write this in a hurry. If not understand I can explain more clear. Please let me know.

 

I [current] can go 2 directions:
R2, R1, and 9 V back to ground
OR
R3, R4, 12 V back to ground.

hi S,
Are you sure about this statement.?
E

 

Question is, find voltage at point B.
Total voltage 12 V - 9 V = 3 Volts
Total resistance = (47+27+56+20)10^3 = 150000 Ohms
Circuit current = V/R = 3/150000 = 0.00002 Amps

I can go 2 directions:
R2, R1, and 9 V back to ground
OR
R3, R4, 12 V back to ground.

R2+R1 = 74000 Ohms * 0.00002 Amps = 1.48 Volts
R3 + R4 = 76000 Ohms * 0.00002 Amps = 1.52 Volts

9 - 1.48 = 7.52 Volts
12 - 1.52 = 10.48 Volts

From my understanding it should be add voltage drops and then subtract from voltage source. Going both directions does not give same result but it should. Answer should be 10.48 Volts meaning I should do 9+1.48 but why is one side subtract from voltage source and one is add voltage source?

I write this in a hurry. If not understand I can explain more clear. Please let me know.

Hi,

You also have to consider the sign of each voltage drop. Some will add and some will subtract from either voltage but you should try to figure out how that works.

Consider the same circuit with all equal resistor values. That means the central voltage at B would be either:
9v+1.5v
or:
12v-1.5v

so you see how we had to add one and subtract another because of the signs of the voltage drops and the signs of the sources.

 

It might be easier for you to calculate the note voltages by using superposition.
For that you include all the resistors in the calculations for each voltage source with the other source at zero volts.
Thus you calculate the voltage at the node for 9V with the 12V source at 0V.
Then you do the same for 12V with the 9V source at 0V.
Then you add these two voltages together at the node to get the total node voltage.

 

From my understanding it should be add voltage drops and then subtract from voltage source. Going both directions does not give same result but it should. Answer should be 10.48 Volts meaning I should do 9+1.48 but why is one side subtract from voltage source and one is add voltage source?

Because in one case you are going in the direction of the current so the voltage drops as you cross each resistor (just like your altitude would drop as you go downstream in a river) while in the other case you are going against the direction of the current sot he voltage rises as you cross each resistor (just like your altitude would rise as you upstream in a river).

 

Ok guys, Thanks for the help.

So take into account of current flow and I will also look into superposition

 

I know your question states you need to find the voltage at B, but you can use associative learning from this superposition calculation at A: