Explanation:
When we measure the emf of a cell by the potentiometer then no current flows in the circuit in zero-deflection condition ie, cell is in open circuit. Thus, in this condition the actual value of a cell is found. In this way, potentiometer is equivalent to an ideal voltmeter of infinite resistance.
Note. The emf in the potentiometer is measured by null method in which zero deflection position is found on the wire.
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$8\ \pi\text{r}^2\text{S}$
$12\ \pi\text{r}^2\text{S}$
$16\ \pi\text{r}^2\text{S}$
$24\ \pi\text{r}^2\text{S}\cdot$
When light wave suffers reflection at the interface from air to glass, the change in phase of the reflected wave is equal to
| (a) 0 |
(b) 
|
(c) 
|
(d) 2
|
Eight drops of mercury of equal radii possessing equal charges combine to form a big drop. Then the capacitance of bigger drop compared to each individual small drop is
|
(a) 8 times |
(b) 4 times |
(c) 2 times |
(d) 32 times |
Which is a wrong statement
|
(a) The Wheatstone bridge is most sensitive when all the four resistances are of the same order |
|
(b) In a balanced Wheatstone bridge, interchanging the positions of galvanometer and cell affects the balance of the bridge |
|
(c) Kirchhoff's first law (for currents meeting at a junction in an electric circuit) expresses the conservation of charge |
|
(d) The rheostat can be used as a potential divider |
An oil drop having charge 2e is kept stationary between two parallel horizontal plates 2.0 cm apart when a potential difference of 12000 volts is applied between them. If the density of oil is 900 kg/m3, the radius of the drop will be
|
(a) 2.0 |
(b) 1.7 |
(c) 1.4 |
(d) 1.1 |
