Calculating Potential Difference Between Points A and B

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To calculate the potential difference between points A and B in the circuit with a 2A current, the user is confused about the application of Ohm's Law and the concept of voltage in a circuit. They correctly identify that the voltage drop across the 3-ohm resistor is 6V, but struggle with the effects of the -20V battery and the direction of current flow. The suggestion is to apply Kirchhoff's loop law to determine the electromotive force (EMF) and the correct signs for points A and B. If the calculated EMF is positive, the signs are correct; if negative, they need to be reversed. Understanding these principles is crucial for solving the potential difference accurately.
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Homework Statement


a current of 2A is flowing from a to b.
what is the potential difference between the points?

______a______3ohm_____-20V+_____1ohm_______+6V-________b_____


hopefully my diagram makes sense.


Homework Equations


this is a really simple question and i can't answer it because I am not understanding the whole concept.
Does current (or anything) stay constant in a cicuit??
do i follow the current round/thru circuit and do calcs along the way?
so voltage after 3ohm-R = IR = 6V
so 6V into 20V battery. now I am stuck. it goes into neg term first so is that -20V?? please help somene! thanks


The Attempt at a Solution

 
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If you assume a battery of EMF E volt is connected across the a and b such that a end is +ve and b end is -ve. Apply loop law, and find E. If you get E +ve, signs of a and b correct. If you get E -ve, reverse the signs of a and b.
 

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