A potentiometer is a circuit to measure emfs. In the diagram with switch S1 closed and S2 open, there is no current through the galvanometer G for R1 = 20.0 Ω with a standard cell „°s of 2.00 V. With switch S2 closed and S1 open, there is no current through the galvanometer G for R2 = 80.0 Ω.
(a) What is the unknown emf „°x?
(b) Explain why the potentiometer accurately measures the emf even for a source with substantial internal resistance.

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20.0 V