Question

Two identical cells send the same current in $2 \Omega$ resistance, whether connected in series or in parallel. The internal resistance of the cell should be

• A. $1 \Omega$
• B. $2 \Omega$
• C. $\frac { 1 } { 2 } \Omega$
• D. $2.5 \Omega$

Answer 1

Answer: (B)

$2 \Omega$

Answer 2

In series, $i _ { 1 } = \frac { 2 E } { 2 + 2 r }$

In parallel, $i _ { 2 } = \frac { E } { 2 + \frac { r } { 2 } } = \frac { 2 E } { 4 + r }$

Since $\frac { 2 E } { 4 + r } = \frac { 2 E } { 2 + 2 r }$ ⇒ $r = 2 \Omega$