Dielectrics question from MHT CET 2025 (26 Apr, Shift 1)

Answer: (a)

1. The dielectric fills half the plate area across the full gap, so the two halves are in parallel.
2. Each half alone has capacitance $\frac{C_0}{2}$; the dielectric half becomes $\frac{KC_0}{2}$.
3. $C_n = \frac{KC_0}{2} + \frac{C_0}{2} = \frac{(K+1)C_0}{2}$.
4. So $\frac{C_n}{C_0} = \frac{K+1}{2}$, answer (a).