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A student uses the circuit diagram of a potentiometer as shown in Fig. (a) For a steady current I passing through thepotentiometer wire, he gets a null point for the cell epsi_1and not for epsi_2 . Give reason for this observation and suggest how thisdifficulty can be resolved. (b) What is the function of resistance R used inthe circuit? How will the change in its value affect the null point ?(c ) How can the sensitivity of the potentiometer be increased? |
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Answer» Solution :(a) The student does not get a null point for the cell `epsi_2` because cell `epsi_2`is connected in the circuit wrongly. The difficulty can beresolved by connecting + ve terminal of `epsi_2`to point A and - ve terminal to key .b.. (b) The resistance R reduces the current PASSING through the galvanometer when the jockey contactis FAR away from the null point. As a result, the galvanometer is protected from the damage likely to be caused by a STRONG current. A change in value of resistance R does not affect the null point. (c) Sensitivity of the potentiometer can be increased by lowering the value of potential gradient along the potentiometer wire. It can be achieved (i) by INCREASING the total length of potentiometer,(ii) by placing a resistance in the auxiliary circuit of DRIVER cell in series of the potentiometer. |
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