[单选题]
An electric circuit dmkrn6 v l/ 7r7rv06y7p 9-sdsygal8 ukfm)t vglgpeq;h.,-6k7g3u r with emf $ϵ$ and internal resistance r is connected to a variable resistor R which varies from 0 Ω to 6Ω.
The variation of the power dissipated in the resistor R with the value of the resistance R is shown in the graph.
What is the value of $ϵ$, if the maximum dissipated power is when R is equal to the internal resistance of the battery $r$ ?
