A voltmeter has resistance of 100 ` Omega ` . What will be its reading when it is connected across a cells of e.m.f 2 V and internal resistance 20 ` Omega ` ?

Explanation

Given : ` R _ V = 100 Omega , E = 2V, r = 200 Omega`

Let I be the current drawn from the cell.
Applying Kirchhoff's voltage law,
` E - IR_V - I r = 0 `
` therefore I = ( E ) /( R _ V + r ) `
` = ( 2 ) /( 100 + 20 ) = ( 1 ) /( 60 ) A `
The volmeter measures the terminal p.d. ( V) of the cell.
` V = IR_V `
` = ( 1 ) / ( 60 ) xx 100 = 1.667 V `