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(a) For the circuit shown in the figure, how would the balancing length be affected, if(i) R_1 is decreased, (ii) R_2 is increased, the other factors remaining the same in the circuit ?Justify your answer in each case. (b) Why is a potentiometer preferred over a voltmeter ? Give reason. |
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Answer» Solution : (a) (i) When `R_1` is decreased, the current flowing in the POTENTIOMETER wire AB and consequentlythe POTENTIAL gradient along the potentiometer wire increases. As a result, the balancinglength decreases i.e., the balancing point shifts towards left (towards point A). (ii) When `R_2` is increased, the current flowing through `R_2`decreases and as a result the potentialdifference across the terminals of the CELL, whose internal resistance is to be determined, increases `[V = epsi- Ir]` . As a result, the balancing length increases, i.e., the balancing pointshifts towards right (towards the point B). (b) A potentiometer is preferred over a VOLTMETER for MEASURING potential differences and emf of cells because measurement is done here in balance condition, when no current is being drawn fromthe given cell. |
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