Shown in the figure is a circular loop of radius `r` and resistance `R`. A varible magnetic field of induction `B=B_(0)e^(-t)` is established inside the coil. If the key `(K)` is closed, the electrical power devloped right after closing the switch is equal to

Explanation

`E = (-d phi)/(dt) = -A.(dB)/(dt)` or `E = -pir^(2)(d)/(dt)(e^(-t))`
`rArr E = pi r^(2) e^(-t)` , `P = (E^(2))/(R ) = (pi^(2)r^(4)e^(-2t))/(R )` , at `t = 0 , P = (pi^(2) r^(4))/(R )`