# How to calculate the voltage across Va and Vb?

Attached is the circuit I have been analyzing. Here the intention is to calculate the voltage across V_A and V_B - (See the red colored letters in the circuit diagram.)

I have calculated V_R1 using Kirchhoff's voltage law as follows, Edit I have taken voltage across V_A and V_B as follows, Can anyone verify the calculation.

• In your first calculations you get $V_{R1} = 1.2\ V$. Then in your second calculation you use 1.8 V. – The Photon Sep 30 '19 at 17:01
• A good way to check your work is to use Ohm's Law to calculate all of the resistor currents, and then verify that KCL holds at all of the nodes. Learning to check your own work is an important skill. – Elliot Alderson Sep 30 '19 at 17:07
• @ThePhoton, update the question with correction you have pointed out – student7 Sep 30 '19 at 17:12
• Pay careful attention to the signs of the voltage sources. – Brian Drummond Sep 30 '19 at 17:26

The situation is very simple: Because we know that the voltage at point A is 7 volts higher than the voltage at point C. And also That the voltage at point B is 1.8V higher than the voltage at point C.

Therefore we can easily find the V_AB voltage.

Can you do it?

• I am considering a loop with V1, V_AB and V_R4, -> -V_1 + V_AB + V_R4 =0 => -7 V + V_AB + 1.8 V = 0 => V_AB = 5.2 V. Make sense :-) ? – student7 Sep 30 '19 at 17:39
• But in this example doing the loop is a hard way. But we can find it this way V_AB = V_A - V_B = 7V - 1.8V = 5.2V – G36 Sep 30 '19 at 17:44
• As I am a beginner, I do't have an option to up-vote your comments and answer. But this clarifies my question. Thank you. – student7 Sep 30 '19 at 17:47
• More about voltage electronics.stackexchange.com/questions/392010/… – G36 Sep 30 '19 at 17:51
• Let C=0, B=+1.8V, R1+=7V, R1-=1.8-10V=-8.2V. Therefore V(theR1= +7V-(-8.2V)=+15.2V. Capiche? – Tony Stewart Sunnyskyguy EE75 Oct 4 '19 at 22:30