Q. 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 decreases its range to $I/n$?
A) $\frac{R_{0}}{n}$
B) $\frac{R_{0}}{(n - 1)}$
C) $\frac{R_{0}}{(n + 1)}$
D) None of these
Explanation
(d) 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 $I < I_{g}$.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.