To find an unknown EMF using a voltage divider.
Slide wire potentiometer, 7.5, 6, and 1.5 volt batteries, 5 amps DC center zero projection meter, knife switch and momentary switch.
A 7.5 volt battery (voltage V) is connected across a resistive wire of length L. A second "unknown" lesser voltage can be determined experimentally as follows: Connect the second source, with the same polarity as the standard source, to one end of the test wire through a galvenometer and a key switch to a clip lead. Find the distance L(1) along the wire where the clip lead draws no current. The unknown voltage V(u) is then: ◙V(u) = V L(1) / L.