Home MCQs EEJ MAIN Physics Question #6992
Back to Questions
EEJ MAIN Physics QUESTION #6992
Question 1

A parallel plate capacitor with square plates is filled with four dielectrics of constants $K_1, K_2, K_3, K_4$ arranged in a $2 \times 2$ grid (left-right half and top-bottom half). The effective dielectric constant $K$ is:

  • $K = \dfrac{(K_1+K_3)(K_2+K_4)}{K_1+K_2+K_3+K_4}$
  • $K = \dfrac{(K_1+K_2)(K_3+K_4)}{2(K_1+K_2+K_3+K_4)}$
  • $K = \dfrac{(K_1+K_2)(K_3+K_4)}{K_1+K_2+K_3+K_4}$✔️
  • $K = \dfrac{(K_1+K_4)(K_2+K_3)}{2(K_1+K_2+K_3+K_4)}$
Correct Answer Explanation

The four dielectrics fill four quadrants. Each half of the plate area (left and right halves, each of width $d/2$) acts as two capacitors in series (top and bottom dielectrics), and these two series combinations are in parallel.

More directly using the standard result for this arrangement:

$K_{eff} = \frac{(K_1+K_2)(K_3+K_4)}{K_1+K_2+K_3+K_4}$

This comes from treating left column ($K_1, K_3$ in series) in parallel with right column ($K_2, K_4$ in series), where each column occupies half the area and full thickness $d$, but each dielectric occupies half the thickness $d/2$.