What is the maximum power output that can be obtained from a cell of $\operatorname{emf} E$ and internal resistance $r ?$

• A

  $2 E^{2} / r$
• B

  $E^{2} / 2 r$
• Correct answer
  C

  $E^{2} / 4 r$
• D

  None of these

Hence, the correct answer is option: 'C'.