Question

When a resistance of $2$ ohm is placed across a battery, the current is $1A$. And when the resistance across the terminals is $17$ ohm, the current is $0.25A$. The electromagnetic force of the battery is

• A. $4.5V$
• B. $5V$
• C. $3V$
• D. $6V$

Answer 1

The correct option is B $5V$

Case 1

$R=2\Omega I=1A$
$E=I[R+r]$

$E=2+r\Rightarrow E-r=2$ .......(1)
Case 2
$R=17\Omega I=0.25A$
$E=\frac{1}{4}17+r$
$4E-r=17$ ..........(2)
(2) - (1)
$3E=15\Rightarrow E=5V$