# Measuring unknown emf by potentiometer

in measuring unknown emf by potentiometer, why must the stable current source(working battery) have a voltage greater than any voltage to be measured?

i cant understand why..
in our exercise in physics, we used a slide-wire potentiometer with the assumption that 1 meter of the slide-wire gives a voltage drop of 1V. so, the battery we used has an emf slightly greater than 2 volts.

is there a connection between the length of the slide wire used and the use of a battery with an emf greater than 2V?

i am currently doing our physics lab report and honestly, its part of the discussion. im asking for help for i cant understand.

tanx to anybody who dares to reply..

## Answers and Replies

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Andrew Mason
Science Advisor
Homework Helper
tin llenaresas said:
in measuring unknown emf by potentiometer, why must the stable current source(working battery) have a voltage greater than any voltage to be measured?

i cant understand why.
Because you are finding the point along a length of an electrical resistance where the voltage is equal (and opposite) to the voltage you are trying to measure. The potential difference goes from 0 to maximum along that resistance, maximum being the voltage across the entire length.

If the voltage across that entire length is not greater than the voltage you are trying to measure, there will be no point where it is equal to the measured voltage.

AM

tanx buddy.ü