A potentiometer is a null type resistance network device for measuring potential differences.For the accurate measurement of potential difference, current and resistance the potentiometer is one of the most useful instruments. Its principle of action is that an unknown emf or P.D. is measured by balancing it, wholly or in part, against a known potential difference.
A simplest potentiometer consists of wire LM of uniform cross-section, stretched alongside a scale and connected across battery of potential V. A standard cell of known emf E is connected between L and terminal 1 of a two way switch S.Working Slider N is pressed momentarily against wire LM and its position is adjusted until the galvanometer deflection is zero when N is making contact with LM. Let l1 be the corresponding distance between L and N.The fall of potential over length l1 of the wire is then the same as the emf E2 .Thenmove the switch to 2, thereby replacing the standard cell by another cell, the e.m.f E2of which is to be measured. Adjust the slider N again to give zero deflecton on G. If l2 be the new distance between L and N, then E2/E1 = l2/l1E2 = l2 x E1/l1
Applications of potentiometer
Following are the applications of potentiometer
- 1. Measurement of small e.m.f (upto 2V)
- 2.Comparnison of e.m.fof two cells
- 3. Measurement of high e.m.f( say 250 V)
- 4. Measurement of resistance
- 5.Measurement of current
- 6. Calibration of ammeter
- 7. Calibration of voltmeter
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