A multirange voltmeter can be constructed by using a galvanometer circuit as shown in figure. We want to construct a voltmeter that can measure 2V, 20V and 200V using a galvanometer of resistance `10Omega` and that produces maximum deflection for current of `1mA`. Find `R_1`, `R_2` and `R_3` that have to be used.

Options

A. `18kOmega`
B. `180kOmega`
C. `1.8kOmega`
D. `1800kOmega`

Answer

1

Explanation

Here, `I_(g)=1mA=1xx10^(-3)A,G=10Omega`
`R_(1)=?, R_(2)=?,R_(3)=?`
Using `R+G=(V)/(I_(g))`

At point `P,R_(1)+10=(2)/(10^(-3))2000Omega`
`R_(1)=2000-10=1990Omega=1.9kOmega`
At point `Q,R_(1)+R_(2)+10=(20)/(10^(-3))=20000Omega`
`R_(2)+2000=20000`
`:. R_(2)=18000Omega=18kOmega`
At point `R,`
`R_(1)+R_(2)+R_(3)+10=(200)/(10^(-3))=200000Omega`
`:. R_(3)=200000-1990-18000-10`