Shunt Resistance For Ammeter Conversion — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Shunt Resistance for Ammeter Conversion Used in the design of ammeters to convert a sensitive galvanometer into a device capable of measuring larger currents by diverting the majority of current through a low-resistance path. The galvanometer (resistance G) and shunt (resistance S) are connected in parallel. The total current I splits at the junction: I g flows through the galvanometer, and I - I g flows through the shunt. Since the components are parallel, the potential difference across them is equal: V G = V S. Using Ohm's Law (V=IR), equate the voltages: I g G = (I - I g) S. Solve algebraically for S: S = (I g G) / (I - I g). The measured current I must be strictly greater than the full-scale deflection current I g. The shunt resistance S must be connected in parallel with the galvanometer. Assumes temperature stability of resistances during operation. Students often incorrectly calculate the net resistance of the ammeter as G + S instead of (GS)/(G+S). Confusing the connection type: Shunts are parallel for ammeters, whereas multipliers are series for voltmeters. Using milli-amperes directly in the formula without converting to Amperes relative to I.