If E_induced in dielectric in a capacitor is asked should I use E=E_•/K or E = E_•(1-1/K) , K being dielectric const of medium inserted ? Also please mention why .

Dear student,

On application of external field E inside a dielectric, an induced electric field is created.
Due its induction in opposite direction of that of E, the ‘net electric field’ is E/K.

However when we are asked the ‘induced electric field’, the need to tell that tell the value of E-E/K.