A galvanometer shows full scale deflection for a current of 4 mA. It is converted into an ammeter of range from 0 to 8 A by using a shunt. The ratio of resistance of the galvanometer coil to the resistance of the shunt used is nearly:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2000 : 1
Given: Galvanometer full scale current $I_g = 4 \times 10^{-3}\,A$ Range of ammeter $I = 8\,A$
Shunt current: $I_s = I - I_g = 8 - 0.004 \approx 7.996\,A$
Condition for parallel connection: $I_g R_g = I_s R_s$
Therefore, $\frac{R_g}{R_s} = \frac{I_s}{I_g}$
$\frac{R_g}{R_s} = \frac{7.996}{0.004} = 1999 \approx 2000$
Final Answer: $\;\;\;\; \frac{R_g}{R_s} \approx 2000$