Explain the equation of a shunt.

(N/A) shunt is a low-resistance wire connected in parallel with a galvanometer to convert it into an ammeter.
Let $G$ be the resistance of the galvanometer and $I_g$ be the current for full-scale deflection.
Let $I$ be the total current to be measured and $S$ be the resistance of the shunt.
Since the shunt is in parallel with the galvanometer,the potential difference across both is the same:
$V_g = V_s$
$I_g G = (I - I_g) S$
Rearranging for the shunt resistance $S$:
$S = \frac{I_g G}{I - I_g}$
This equation allows us to calculate the required shunt resistance to extend the range of a galvanometer to a desired current $I$.