Class 12 Physics & Chemistry Practical Viva Voce Questions & Answers PDF (30 Marks Practical Target)

It works on the principle of a balanced Wheatstone bridge: when no current flows through the galvanometer, $\frac{P}{Q} = \frac{R}{S}$, which gives unknown resistance $S = \frac{100 - l}{l} R$.

These alloys have a high resistivity and an extremely low temperature coefficient of resistance, ensuring resistance does not change as the wire warms up during current flow.

The Wheatstone bridge is most sensitive when all four arms have comparable resistances ($P \approx Q \approx R \approx S$), minimizing proportional measuring errors.

Parallax is the apparent relative shift between an object and its image when the eye is moved from side to side. It is removed when the tips of the object needle and inverted image needle coincide and move together without relative displacement.

Index error accounts for any discrepancy between the physical distance measured by the needle and the distance shown on the optical bench upright scale.

The forward voltage at which diode current starts increasing exponentially (approximately 0.7 V for Silicon and 0.3 V for Germanium).

In forward bias, current is conducted by majority charge carriers (high density). In reverse bias, current is solely due to thermally generated minority carriers (extremely low density).

Deep purple $\text{MnO}_4^-$ ions are reduced to colorless $\text{Mn}^{2+}$ ions during the reaction. The first drop of excess $\text{KMnO}_4$ imparts a permanent light pink color to the solution, indicating the endpoint without an external indicator.

$\text{HCl}$ reacts with $\text{KMnO}_4$ to liberate chlorine gas ($\text{Cl}_2$), consuming extra titrant. $\text{HNO}_3$ is a strong oxidizing agent itself and would interfere with the redox balance.

Add Nessler's reagent ($\text{K}_2[\text{HgI}_4]$) to the aqueous salt solution in alkaline medium. Formation of a brown precipitate of Millon's base iodide confirms $\text{NH}_4^+$.

To the salt extract, add freshly prepared $\text{FeSO}_4$ solution, then slowly trickle concentrated $\text{H}_2\text{SO}_4$ along the inner side of the test tube. A dark brown ring of nitroso ferrous sulfate ($[\text{Fe}(\text{H}_2\text{O})_5(\text{NO})]\text{SO}_4$) forms at the liquid junction.