40. The capacitor can be viewed as two capacitors C
1
and C
2
in parallel, each with surface area A/2 and
plate separation d, filled with dielectric materials with dielectric constants κ
1
and κ
2
, respectively. Thus
C = C
1
+ C
2
=
ε
0
(A/2)κ
1
d
+
ε
0
(A/2)κ
2
d
=
ε
0
A
d
κ
1
+ κ
2
2
.