1. Choose the correct statement from the following. (A) The potentiometer with more wire length is less sensitive than that with less wire length.

Question

POTENTIOMETER

Potentiometer is preferred over voltmeter to measure emf of a cell because it measures true emf of the cell. It uses null method, so no current is drawn by the galvanometer from the cell in balanced condition of potentiometer. On the other hand, a voltmeter measures the voltage across the terminals of a cell when the cell is in closed circuit, that is, when current is flowing through the cell. This voltage is not equal to the  emf of the cell. In fact, it is equal to the emf minus the potential drop across the internal resistance of the cell. The potentiometer is more sensitive than a voltmeter. The potentiometer measures the emf as well as the terminal potential difference of a cell. Its least count is much better than that of a voltmeter.

1. Choose the correct statement from the following. 

(A) The potentiometer with more wire length is less sensitive than that with less wire length. 

(B) A steady & high current needs to be allowed to make the potentiometer more sensitive. 

(C) Area of cross-section of the wire needs to be high & uniform 

(D) The potentiometer wire needs to have high specific resistance for its material. 

2. Two cells of e.m.f. E1 and E2 are joined in series and the balancing length of the potentiometer wire is 625 cm. If the terminals of E1 are reversed, the balancing length obtained is 125 cm. Given E2>E1, the ratio E1:E2 will be 

(A) 2:3 

(B) 5:1 

(C) 3:2 

(D) 1:5 

3. A potentiometer wire of length 10m is connected in series with a battery. The e.m.f. of a cell balances against 250cm length of wire. If length of potentiometer wire is increased by 1m, the new balancing length of wire will be 

(A) 2m 

(B) 2.25m 

(C) 2.5m 

(D) 2.75m 

4. A potentiometer experiment is set up to compare the e.m.f.s E1, and E2, of two cells. When the null point is obtained, the current is drawn from… 

(A) only the driver cell 

(B) only the cell of e.m.f. E1 

(C) only the cell of e.m.f. E2 

(D) both the driver cell and the cells of e.m.f.s E1, and E2 

5. In the potentiometer of 5 wires, the balance point is obtained on the 2^nd wire. To shift the balance point to the 4^th, we should decrease the current of the main circuit. 

(A) True 

(B) False

Answer 1

1  (C)  Area of cross-section of the wire needs to be high & uniform

2  (B)  5:1

3  (D) 2.75m

4  (A) only the driver cell

5  (A) True