A voltmeter has a range `O - V` with a series resistance `R`. With a series resistance `2R`, the range is `O - V`. The correct relation between `V` and `V'`is

Options

A. `V'=2V`
B. `V'gt2V`
C. `V'lt2V`
D. `V'=V/2`

Answer

C

Explanation

For a voltmeter, the range `V=i_g(R+G)`, where G is the resistance of the galvanometer. For some `I_g, propto (R+G) and V' propto (2R+G)` (Note that G is not doubled) `therefore 2V propto (2R+2G) as (2R + 2G)gt(2R+G)` V' will be less than 2V. (or the reading will be less than double).