Question

A voltmeter of resistance $99\Omega$ connected across a cell, shows a reading of $9.9V$. An ammeter of resistance $1\Omega$ connected to the same cell shows $5A$. The E.M.F. of the cell is

• A. $9.9V$
• B. $14.9V$
• C. $10V$
• D. $9.8V$

Answer 1

Answer: (C)

$10V$

$\Rightarrow I\times 99=9.9$
$I=0.1A$
$\Rightarrow E-Ir=9.9$
$E-0.1r=9.9$ -------------- 1
$E=5(1+r)$ ------------------ 2
Using 1 & 2
$0.1r+9.9=5+5r$
$\frac{4.9}{4.9}=r=1\Omega$
$\Rightarrow E=0.1+9.9$
$E=10V$