A long cylindrical capacitor has an inner electrode of radius $R_1$ and an outer electrode of radius

Question

A long cylindrical capacitor has an inner electrode of radius $R_1$ and an outer electrode of radius $R_2$. The gap between the electrodes is $d = R_2 - R_1$, where $d \ll R_1$, such that the mean radius of the electrodes is approximately $R$. A solid cylindrical layer of dielectric with relative permittivity $K$ exactly fits the gap and is partially inserted into the capacitor. A constant potential difference $V$ is maintained across the electrodes. Fringing effects at the edges can be neglected.

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