A galvanometer having internal resistance `10 Omega` required `0.01` A for a full scale deflection. To convert this galvanometer to a voltmeter of full scale deflection at 120 V, we need to connect a resistance of

Options

A. `11990 Omega` in series
B. `11990Omega` in parallel
C. `12010Omega` in series
D. `12010 Omega` in parallel.

Answer

A

Explanation

Here, galvanometer resistance `G= 10Omega` Current for full scale deflection, `I_(g)= 0.01A`. To convent the galvanometer into a voltmeter of range 120V, a high resistance R is connected in series with it such that
`V= I_(g) (G+R) or 120 = 0.01(10 + R)`
or `R= (120)/(0.01) - 10= 12000- 10= 11990Omega`