Figure shows a potentiometer with a cell of 2.0 V and internal resistance 0.40 Omegamaintaining a potential drop across the resistor wire AB. A standard cell which maintains a constant emf of 1.02 V (for every moderate currents upto a few mA) gives a balance point at 67.3 cm length of the wire. To ensure very low currents drawn from the standard cell, a very high resistance of 600 Omegais put in series with it, which is shorted close to the balance point. The standard cell is then replaced by a cell of unknown emf epsi and the balance point found similarly, turns out to be at 82.3 cm length of the wire. Would the circuit work well for determining an extremely small emf, say of the order of a few mV (such as the typical emf of a thermo-couple)? If not, how will you modify the circuit?

Figure shows a potentiometer with a cell of 2.0 V and internal resista

1.	Figure shows a potentiometer with a cell of 2.0 V and internal resistance 0.40 Omegamaintaining a potential drop across the resistor wire AB. A standard cell which maintains a constant emf of 1.02 V (for every moderate currents upto a few mA) gives a balance point at 67.3 cm length of the wire. To ensure very low currents drawn from the standard cell, a very high resistance of 600 Omegais put in series with it, which is shorted close to the balance point. The standard cell is then replaced by a cell of unknown emf epsi and the balance point found similarly, turns out to be at 82.3 cm length of the wire. Would the circuit work well for determining an extremely small emf, say of the order of a few mV (such as the typical emf of a thermo-couple)? If not, how will you modify the circuit?
Answer» <html><body><p></p><a href="https://interviewquestions.tuteehub.com/tag/solution-25781" style="font-weight:bold;" target="_blank" title="Click to know more about SOLUTION">SOLUTION</a> :The circuit, as it is would be unsuitable, because the <a href="https://interviewquestions.tuteehub.com/tag/balance-891682" style="font-weight:bold;" target="_blank" title="Click to know more about BALANCE">BALANCE</a> <a href="https://interviewquestions.tuteehub.com/tag/point-1157106" style="font-weight:bold;" target="_blank" title="Click to know more about POINT">POINT</a> (for `epsi` of the order of a few mV) will be very close to the end A and the percentage error in measurement will be very large. The circuit is modified by putting a suitable resistor R in <a href="https://interviewquestions.tuteehub.com/tag/series-1201802" style="font-weight:bold;" target="_blank" title="Click to know more about SERIES">SERIES</a> with the wire AB so that potential drop across AB is only slightly greater than the emf to be measured. Then, the balance point will be at <a href="https://interviewquestions.tuteehub.com/tag/larger-1067345" style="font-weight:bold;" target="_blank" title="Click to know more about LARGER">LARGER</a> length of the wire and the percentage error will be much smaller</body></html>

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