JEE Main2018PhysicsCurrent ElectricityActual
A galvanometer with its coil resistance 25 Ω requires a current of 1 mA for its full deflection. In order to construct an ammeter to read up to a current of 2 A the approximate value of the shunt resistance should be:
Options
- A1.25   × 10 - 2  Ω
- B2.5 × 10 - 3 Ω
- C2.5 × 10 - 2 Ω
- D1.25 × 10 - 3 Ω
Correct answer
A. 1.25   × 10 - 2  Ω
Step-by-step solution
From the above figure, it is clear that, I g R g = ( I -   I g ) S S   ≃ 10 - 3 × 25 2 ⇒ S   ≃ 12.5   × 10 - 3 ⇒ 1 .25   × 10 - 2 Ω