A galvanometer gives full-scale deflection at 0.006 A. With a 4990 Ω series resistance it becomes a 0 – 30 a_0–30 a 0 –30 V voltmeter. If a resistance (2n/249) Ω is connected as a shunt, it becomes a 0 – 1.5 a_0–1.5 a 0 –1.5 A ammeter. Find n.
Physics · Current electricity · Electrical Instruments: Galvanometer, Ammeter, Voltmeter & Potentiometer
JEE Advanced 2014

Question

A galvanometer gives full-scale deflection at 0.006 A. With a 4990 Ω series resistance it becomes a 0 – 30 a_0–30 a 0 –30 V voltmeter. If a resistance (2n/249) Ω is connected as a shunt, it becomes a 0 – 1.5 a_0–1.5 a 0 –1.5 A ammeter. Find n.

Physics · Current electricity · Electrical Instruments: Galvanometer, Ammeter, Voltmeter & Potentiometer

JEE Advanced 2014

G1 Physics · Accepted Answer

The galvanometer resistance is 30/0.006 - 4990 = 10 Ω. For a 1.5 A ammeter, the required shunt is S = (0.006×10)/(1.5-0.006) ≈ 0.04 Ω. Since S = 2n/249 Ω, n ≈ 5.

A galvanometer gives full-scale deflection at 0.006 A. With a 4990 Ω series resistance it becomes a 0 – 30 a_0–30 a 0 ​ –30 V voltmeter. If a resistance (2n/249) Ω is connected as a shunt, it becomes a 0 – 1.5 a_0–1.5 a 0 ​ –1.5 A ammeter. Find n.

A galvanometer gives full-scale deflection at 0.006 A. With a 4990 Ω series resistance it becomes a 0 – 30 a_0–30 a 0 –30 V voltmeter. If a resistance (2n/249) Ω is connected as a shunt, it becomes a 0 – 1.5 a_0–1.5 a 0 –1.5 A ammeter. Find n.