Considering the two regions,

.......................(2.120)

Applying the boundary conditions V=0 for z=0 and V=V₀ for z = d, we can write

..................(2.121)

Both the solution should give the same potential at z =a . Therefore,

...........................................(2.122a)

or, ...................................(2.122b)

Another equation relating to A₁ and A₂ is required to solve for the two constants A₁ and A_2.

We note that at the dielectric boundary at z = a , the normal component of electric flux density vector is constant. Noting that , we can write