A galvanometer coil has resistance 20 Ω and the metre shows full scale deflectionfor a current of 2 mA. How will you convert the metre into an ammeter of range 0 to6 A?

Correct option is C

​$$\textbf{Given:} \\\text{Resistance of galvanometer coil, } R_g = 20\,\Omega \\\text{Full-scale deflection current, } I_g = 2\,\text{mA} = 0.002\,\text{A} \\\text{Desired range of ammeter, } I = 6\,\text{A} \\[10pt]\text{To convert the galvanometer into an ammeter, a \textbf{shunt resistor} } (S) \text{ is connected in \textbf{parallel} with the galvanometer.} \\[10pt]S = \frac{I_g R_g}{I - I_g} \\[10pt]S = \frac{0.002 \times 20}{6 - 0.002} = \frac{0.04}{5.998} \approx 0.00666\,\Omega = 6.66\,\text{m}\Omega$$​​