Physics M.C.Q (1 Marks)

Potentiometer is preferred over voltmeter because it measures true emf of the cell. It uses null method so that no current is drawn from cell in balanced condition, as $E - Ir = V$ and $I = 0$ then $V = E.$
Hence emf measurement is more accurate.

$\text{P}=\frac{\text{V}^2}{\text{R}}$
As the resistors on connected in paralled to battorty, both have same patential,
$\text{p}=\frac{1}{\text{R}}$
$\frac{\text{P}_1}{\text{P}_2}=\frac{\text{R}_2}{\text{R}_1}$
$=\frac{6}{4}$
$=\frac{3}{2}$
$3:2$

The resistance of a conductor is directly proportional to its length, inversely proportional to the area of cross$-$section, and nature of the material. The resistance of the conductor does not depend on viscosity.

Power $=\frac{\text{V}^2}{\text{R}},\text{R}\downarrow\text{thanpower}\uparrow$
Because Power $\propto\frac{1}{\text{R}}.$

Equivalent emf $\in_0=\frac{\in_1\text{r}_1+\in_2\text{r}_2}{\text{r}_1+\text{r}_2}$

Equivalent resistance $=\text{r}_0=\frac{\text{r}_1\text{r}_2}{\text{r}_1+\text{r}_2}$
$\phi$ The equivalent emf is smaller than either of the two emfs.
$\phi$ The equivalent internal resistance is smaller than either of the two internal resistances.

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.

Current is uniform throughout the wire even if it is of non$-$uniform thickness. This is because charge passing through every cross sectional area per unit time remains the same throughout the wire. So, current remains the same.

$‘X\ ’$ is a metallic conductor. For small currents, it obeys Ohms’s law and its $V-I$ graph is a straight line. But when large currents are passed through the same conductor, it gets heated up and its resistance increases. It no longer obeys Ohm’s law at higher currents.

Thermistor are made up of substance with high $\alpha ,$ which is very much sensitive to temperature thereby a slight change in temperature varies its resistance with huge amount. hence making more than one value of current possible for chosen non$-$zero value of voltage.

For a balanced Meter Bridge $\frac{\text{P}}{\text{Q}}=\frac{\text{x}}{(100-\text{x})}.$ From this, we can understand that the null deflection of galvanometer does not depend on the radius of the wire. So, even if the radius of the wire is tripled, the null deflection of the galvanometer undergoes no change.