The scale of a galvanometer of resistance `100 ohms` contains 25 divisions. It gives a defelction of one division on passing a current of `4xx 10 ^(-4)` amperes. The resistance in ohms to be added to it, so that it may become a voltmeter of range `2.5` volts is

Options

A. 150
B. 170
C. 110
D. 220

Answer

A

Explanation

The deflection of one division of galvanometer is given by the current = ` 4 xx 10^(-4) A `
or the current sensitivity of galvanometer is
` = 4 xx 10^(-4)` A/div
` i_(g) =` full scale deflection
= current sensitivity `xx` total number of turns
` = 4 xx 10^(-4) xx 25 = 10^(-2) A `
Resistane of galvanometer = `100 Omega` the value of resistance required,
` R = V/i_(g) - G = (2.5)/(10^(-2)) - 100`
= ` 250 - 100 = 150 Omega`