I am ripping my hairs trying to understand this answer, it is written that, for the following set up of two capacitor plates separated by distance $d$ and area $A$ with three dielectrics insert with constant $K_1,K_2$ and $K_3 $
The electric field is not necessarily normal at the boundary joining the dielectric substances $K_1$ and $K_2$. If it is so, precisely, what would be the directions at points along the surface? Would all of the electric field vectors attached to these points be tilted differently or have same tilt amount?
It may be noted that this other answer on a different question says the opposite of this.
Picture sourced from mentioned answer
I had posted a question here on why it must be normal like so with no satisfactory answers.
The electric-static field is always normal to the surface of a conductor at the conductor. But you want to know why it is normal to the plates between the plates. Unfortunately, you won't find a rigorous mathematical proof of that, because it is not rigorously mathematically true. It is approximately true. It is true to a very good approximation, but it is not exactly true. The field lines actually bulge a little away from centre. The effect is small toward the centre of the plates, but gets larger toward the edges. This bulging is generally called "fringe" effects.
This again suggests it is normal but it contradicts the originally quoted answer.
Assume area of plates is large relative to plate seperation