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In the Fig., a long uniform potentiometer wire ABis having a constant potential gradient along its length. The null points for the two primary cells of emf epsi_1 andepsi_2connected in the manner shown are obtained at adistance of 120 cm and 300 cm from the end A. Find (i) epsi_1//epsi_2and (ii) position of null point for the cell epsi_1. How is the sensitivity of a potentiometer increased ? |
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Answer» Solution :(i) If the constant potential gradient be k volt/cm then as PER question `epsi_1 + epsi_2 = k xx 300`....(i) `epsi_1 - epsi_2 = k xx 120`....(ii) `rArr (epsi_1+ epsi_2)/(epsi_1- epsi_2) = 300/120 = 5/2 rArr epsi_1/epsi_2 = 7/3` (ii) If for the cell `epsi_1` the null point be at a distance of 1 from end A, then `epsi_1 = kl` Dividing (i) by (iii), we have `(epsi_1 + epsi_2)/(epsi_1) = 1 + epsi_2/epsi_1 = (300)/(l) " or"1 + 3/7 =(300)/(l)` ` rArr l = (300 xx 7)/(10) = 210 cm` The SENSITIVITY of a POTENTIOMETER can be increased by (i) increasing the length of thepotentiometer WIRE, and (ii) introducing a high resistance in series of potentiometer. |
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