A galvanometer of resistance 520 Ω is shunted with 20 Ω resistance to convert it into an ammeter. The resistance of the ammeter will be

19.3 Ω

The correct answer is Option (3) → 19.3 Ω

Given:

Galvanometer resistance, $G = 520\,\Omega$

Shunt resistance, $S = 20\,\Omega$

Equivalent resistance of the ammeter:

$R_A = \frac{G \times S}{G + S}$

$R_A = \frac{520 \times 20}{520 + 20} = \frac{10400}{540} = 19.26\,\Omega$

∴ The resistance of the ammeter is $19.26\,\Omega$.