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

The correct option is 19.3 Ω.

Step-by-Step Explanation:

To convert a galvanometer into an ammeter, a low resistance (called a shunt resistance) is connected in parallel with the galvanometer.

When two resistors are connected in parallel, their equivalent resistance, which represents the total resistance of the ammeter ($R_a$), is calculated using the formula for parallel combination:

$\frac{1}{R_a}=\frac{1}{G}+\frac{1}{S}$

where:
$G$ is the resistance of the galvanometer = 520 Ω
$S$ is the shunt resistance = 20 Ω

Rearranging the formula to solve for $R_a$ gives:

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

Substitute the given values into the equation:

$R_a=\frac{520\times 20}{520+20}$

$R_a=\frac{10400}{540}$

Simplifying the fraction:

$R_a\approx 19.259\Omega$

Rounding this to one decimal place, we get:

$R_a\approx 19.3\Omega$

Thus, the resistance of the converted ammeter is approximately 19.3 Ω.