Question: A galvanometer can be converted into an ammeter of desired range by connecting a:
Step 1 (Governing Principle): [0.25 Mark]
To convert a galvanometer of resistance $G$ into an ammeter of range $I$, a shunt resistance $S$ must be connected in parallel with the galvanometer. This is done to bypass the majority of the current through the shunt, protecting the galvanometer coil from damage and reducing the overall resistance of the circuit.
Step 2 (Mathematical Derivation): [0.5 Mark]
Let $I_g$ be the full-scale deflection current of the galvanometer. Since the shunt $S$ is in parallel with the galvanometer $G$, the potential difference across both must be equal:
Solving for the shunt resistance $S$:
$$S = \frac{I_g \cdot G}{I - I_g}$$Since $I \gg I_g$, the value of $S$ must be very small to allow the bulk of the current to pass through the shunt path.
Step 3 (Final Concluded Answer): [0.25 Mark]
The correct option is (C) small resistance in parallel.
💡 EL10 Concept Insight: Think of the galvanometer as a delicate straw that can only handle a tiny sip of water; by adding a wide pipe (the small shunt resistance) in parallel, you let the rest of the "water" (the current) flow safely around the straw so it doesn't burst.