Advertisements
Advertisements
प्रश्न
State the working principle of a potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primary cells. Obtain the required expression used for comparing the emfs.
उत्तर
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),
`E_1/E_2 = I_1/I_2` .....(3)
Thus we can compare the emfs of any two sources. Generally, one of the cells is chosen as a standard cell whose emf is known to a high degree of accuracy.
APPEARS IN
संबंधित प्रश्न
Write two factors by which current sensitivity of a potentiometer can be increased.
Two students ‘X’ and ‘Y’ perform an experiment on potentiometer separately using the circuit given below:
Keeping other parameters unchanged, how will the position of the null point be affected if
(i) ‘X’ increases the value of resistance R in the set-up by keeping the key K1 closed and the Key K2 opens?
(ii) ‘Y’ decreases the value of resistance S in the set-up, while the key K2 remains open and they K1 closed?
Justify.
The emf of a cell is balanced by a length of 120 cm of a potentiometer wire. When the cell is shunted by a resistance of 10 Ω, the balancing length is reduced by 20 cm. Find the internal resistance of the cell.
Which of the following instruments is not a direct reading instrument?
The resistivity of potentiometer wire is 40 × 10-8 ohm - metre and its area of cross-section is 8 × 10-6 m2. If 0.2 ampere current is flowing through the wire, the potential gradient of the wire is ______.
The emf of the cell of internal resistance 1.275 Ω balances against a length of 217 cm of a potentiometer wire. Find the balancing length when the cell is shunted by a resistance of 15 Ω.
State dimension of potential gradient.
What is the internal resistance of the cell?
Draw neat labelled diagram of potentiometer as voltage divider.
