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



.