Question

The proper resistance to connected in series with a voltmeter, in order to increase its range 10 times will be

• A. nine times the resistance of voltmeter
• B. ten times the resistance of voltmeter
• C. eleven times the resistance of voltmeter
• D. one-tenth the resistance of voltmeter

Answer 1

The correct option is A nine times the resistance of voltmeter

Let initial range be $V$
$V=IR$
I will be full scale deflection current
Now, range is to be made $10V$
$10V=I{R}^{\prime }$
$R^{\prime }=10V/\left(V/R\right)=10R$
Therefore, series resistance will be
$R_s=R^{\prime }-R$
$R_s=9R$
option(A)