Question

A circuit diagram of an instrument is given below.

1. Identify the instrument and state the principle of this instrument

2. Modify the circuit diagram to compare the emf of two cells.

3. How can increase the sensitivity of this instrument?

Answer 1

1. Potentio meter 

2. Comparison of e.m.f of two cells using potentiometer

a. Principle:

Potential difference between two points of a current carrying conductor (having uniform thickness) is directly proportional to the length of the wire between two points.

b. Circuit details :

A battery (B₁), Rheostat and key are connected in between A and B. This circuit is called primary circuit. Positive end of E₁ and E₂ are connected to A and other ends are connected to a two way key. Jockey is connected to a two key through galvanometer. This circuit is called secondary circuit.

c. Working and theory :

Key in primary circuit is closed and then E₁ is put into the circuit and balancing length l₁ is found out. 

Then E₁ ∝ l₁ …………(1)

Similarly E₂ is put into the circuit and balancing length (l₂) is found out.

Then, E₂ ∝ l₂ (2)

Dividing Eq (1) by Eq (2),

\(\frac{E_1}{E_2}\) = \(\frac{l_1}{l_2}\) ..........(3)

3. Increase the length of potentio meter wire.