Correct Circuit for Verification of Ohms Law

To verify Ohm's law for a test resistor $R_T$, one needs to measure:

1. The potential difference across the test resistor using a voltmeter.
2. The current flowing through the circuit (and hence through the test resistor) using an ammeter.

Conversion of a Galvanometer into a Voltmeter:

A voltmeter must have a very high resistance so that it draws negligible current from the circuit when connected across a component.

• A galvanometer is converted into a voltmeter by connecting a large (high) resistance in series with it.
• Given that $R_1$ is a high resistance, the voltmeter combination consists of galvanometer $G_1$ connected in series with $R_1$.
• This voltmeter combination $(G_1 + R_1)$ must be connected in parallel with the test resistor $R_T$.

Conversion of a Galvanometer into an Ammeter:

An ammeter must have a very low resistance so that it does not significantly alter the total resistance of the circuit when connected.

• A galvanometer is converted into an ammeter by connecting a small resistance (shunt) in parallel with it.
• Given that $R_2$ is a small resistance, the ammeter combination consists of galvanometer $G_2$ connected in parallel with $R_2$.
• This ammeter combination must be connected in series with the test resistor $R_T$.

Circuit Analysis of Option C:

• Across the test resistor $R_T$, the galvanometer $G_1$ is connected in series with the high resistance $R_1$ (forming an ideal voltmeter in parallel with $R_T$).
• In series with the test resistor $R_T$, the galvanometer $G_2$ is shunted with the small resistance $R_2$ (forming an ammeter in series with $R_T$).
• The entire arrangement is connected to the variable voltage source $V$.

Thus, the circuit shown in Option C correctly configures the measuring instruments to verify Ohm's law.

Therefore, the correct option is C.