The Attempt at a Solution
I redrew the circuit as follow:
Is this correct (or even useful in the first place)?
Anyway when switch S1 is closed, the total resistance = rx + ry, the internal resistances of the batteries.
But when both switches are closed, I figured that the voltage increased by 0.02V, to 0.07V. However I am not sure this is the voltage across which components because the millimeter is connected in a rather strange way.
I'm lost from here onwards. I'm mostly troubled by the placement of the millivoltmeter I guess.
Am I on the right track? Any alternative method?
The answer is (A) by the way.
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