Question

To decrease the range of an ammeter, its resistance need to be increased. An ammeter has resistance $R_0$ and range I. Which of the following resistance can be connected in series with it to decrease its range to $\frac{1}{n}$ ?

• A. $\frac{R_0}{n}$
• B. $\frac{R_0}{(n - 1)}$
• C. $\frac{R_0}{(n + 1)}$
• D. None of these

Answer 1

Answer: (D)

None of these

Answer 2

A galvanometer can be converted into an ammeter by using a low resistance wire in parallel with the galvanometer. The range of ammeter can be increased but cannot be decreased. The reason is that a series resistor cannot change the current that will produce full deflection. A shunt connected in parallel is given by $S = \frac{I_g G}{I - I_g}$ If $I < I_g$ , then the value of S is negative. Hence, a galvanometer cannot be converted into an ammeter of range $I < I_g$