Question

State the working principle of potentiometer.Explain with the help of circuit diagram how the emf of two primary cells are compared by using potentiometer


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Answer 1

Answer:

1. The principle of a potentiometer is that the potential dropped across a segment of a wire of uniform cross-section carrying a constant current is directly proportional to its length. The potentiometer is a simple device used to measure the electrical potentials (or compare the e.m.f of a cell

Working principle of Potentiometer:

When a constant current is passed through a wire of uniform area of cross-section, the potential drop across any portion of the wire is directly proportional to the length of that portion.

Applications of Potentiometer for comparing emf of two cells:

The following Figure shows an application of the potentiometer to compare the emf of two cells of emf E1 and E2

E1, E2 is the emf of the two cells.

1, 2, 3 forms a two-way key.

When 1 and 3 are connected, E1 is connected to the galvanometer (G).

Jokey is moved to N1, which is at a distance l1 from A, to find the balancing length.

Applying loop rule to AN1G31A,

Φ l1 + 0 − E1 = 0 ..(1)

Where Φ is the potential drop per unit length

Similarly, for E2 balanced against l2 (AN2),

Φ l2 + 0 −E2 = 0 ..(2)

From equations (1) and (2),

E1E2=I1I2 .3

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Answer 2

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