තවම උත්තරයක් නැත...
You got it mixed up...
at t= 0 (as soon as the battery is connected) the rate of change of current di/dt is not zero and is finite. So there is a back emf in the inductor which is L*(di/dt) till the current reaches the maximum value (which is governed by the resistance in the circuit - if there is no resistor, there is an inherent resistance in the coil of the inductor - it is not zero - which limits the current)
Once the current reaches it's maximum di/dt=0 and the inductor no longer operates and there is no back emf.
It is di/dt that matters!
You got it mixed up...
at t= 0 (as soon as the battery is connected) the rate of change of current di/dt is not zero and is finite. So there is a back emf in the inductor which is L*(di/dt) till the current reaches the maximum value (which is governed by the resistance in the circuit - if there is no resistor, there is an inherent resistance in the coil of the inductor - it is not zero - which limits the current)
Once the current reaches it's maximum di/dt=0 and the inductor no longer operates and there is no back emf.
It is di/dt that matters!

Yes... In fact you yourself stated in your original post!ඔයා කියන්නෙ ස්විච් එක දාපු ගමං ඇතිවෙන ධාරා වෙනස බින්දුවක් නෙමේ කියල
and is finite කිව්වෙ![]()

Yes... and the back emf persists till the current ramps up. When the current remains steady, obviously di/dt=0 (there is to rate of change of current) and there is no back emf. When you switch off exactly the same happens in the reverse direction.
emf ekak hadenna ac wennama oni ne bn? @AnuradhaRa`ඒත් මේ කොයිල් එකේ හටගන්න වි.චු ක්ෂේත්රය ටික ටික අඩු වෙනව. ´ එහෙම වෙන්නැ,dc - emf නියතයි
Ac-emf වාචල්යයි.
ඔව්emf ekak hadenna ac wennama oni ne bn? @AnuradhaRa