A battery of emf `E` and internal resistance `r` is connected is to external resistance `B` The maximum point is the external circuit is `9W` The current flowing in the circuit under the condition is `3A` What is the value of `E` in volt ?

Answer

6

Explanation

Refer there will be maximum power in the external circuit if `R = r`

Maximum power connected,
`P_(max) = ((E )/(r+r))^(2) xx r = (E^(2))/(4r) = 9`…..(i)
Current, `I = (E )/(r+r) = 3 or E = 6V`.....(ii)
Solving (i) and (ii) we get `E = 6V`