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.
Advertisements
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
State the principle of working of a potentiometer.
In the figure a long uniform potentiometer wire AB is having a constant potential gradient along its length. The null points for the two primary cells of emfs ε1 and ε2 connected in the manner shown are obtained at a distance of 120 cm and 300 cm from the end A. Find (i) ε1/ ε2 and (ii) position of null point for the cell ε1.
How is the sensitivity of a potentiometer increased?
Why is a potentiometer preferred over a voltmeter for measuring emf?
When the null point is obtained in the potentiometer, the current is drawn from the ______
A cell of e.m.f 1.5V and negligible internal resistance is connected in series with a potential meter of length 10 m and the total resistance of 20 Ω. What resistance should be introduced in the resistance box such that the potential drop across the potentiometer is one microvolt per cm of the wire?
The emf of a standard cell is 1.5V and is balanced by a length of 300 cm of a potentiometer with a 10 m long wire. Find the percentage error in a voltmeter that balances at 350 cm when its reading is 1.8 V.
In a potentiometer experiment, when the galvanometer shows no deflection, then no current flows through ____________.
The instrument among the following which measures the e.m.f of a cell most accurately is ______
In a potentiometer arrangement, a cell of emf 1.20 V gives a balance point at 36 cm length of wire. This cell is now replaced by another cell of emf 1.80 V. The difference in balancing length of potentiometer wire in above conditions will be ______ cm.
A potentiometer wire AB having length L and resistance 12r is joined to a cell D of emf ε and internal resistance r. A cell C having emt `ε/2` and internal resistance 3r is connected. The length AJ at which the galvanometer as shown in the figure shows no deflection is ______.
