Question

Five identical cells each of internal resistance $1 \,\Omega$ and emf $5 \,V$ are connected in series and in parallel with an external resistance '$R$'. For what value of '$R$', current in series and parallel combination will remain the same ?

• A. $1 \, \Omega$
• B. $25 \, \Omega$
• C. $5 \, \Omega$
• D. $10 \,\Omega$

Answer 1

Answer: (A)

$i_{1}=\frac{25}{5+R}$
$i_{2}=\frac{5}{R+\frac{1}{5}}$
$i _{1}= i _{2} $
$\Rightarrow 5\left( R +\frac{1}{5}\right)=5+ R$
$4 R =4$
$R =1\,\Omega$