Question

An ammeter has a range I with resistance $R_o$, which of the following resistance can be connected in series with it to decrease it range, to$\frac{I}{n}$:

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

Answer 1

The correct option is B $R_o(n-1)$

Suppose series resistance $R^{\prime }$ is connected in series to it

Thus current become $I/n$

Before and after connecting $R^{\prime }$, the voltage $V$

Would remain same

From ohm's law

$\Rightarrow V=I{R}_0=\frac{I}{n}(R_0+R^{\prime })$

Rearrange to get

$R^{\prime }=R_0(n-1)$