Question

The electric fields of dielectrics having the same cross sectional area in series are related to their relative permittivities in which way?

(a) Directly proportional

(b) Inversely proportional

(c) Equal

(d) Not related

This question was posed to me in a job interview.

My question is based upon Composite Dielectric Capacitor in portion Capacitance and Capacitors of Basic Electrical Engineering

Answer 1

Right answer is (b) Inversely proportional

The best I can explain: Let us consider two plates having fields E1 and E2 and relative permittivities e1 and e2. Then, E1=Q/(e0*e1*A) and E2=Q/(e0*e2*A), where e0=absolute permittivity and A=area of cross section. From the given expression, we see that E1/E2=e2/e1, hence the electric field is inversely proportional to the relative permittivities.