A parallel plate capacitor is made of two dielectric blocks in series. One of the blocks has thickness \(d_1\) and dielectric constant \(K_1\) and the other has thickness \(d_2\) and dielectric constant \(K_2,\) as shown in the figure. This arrangement can be thought as a dielectric slab of thickness \(d=(d_1+d_2),\) and effective dielectric constant \(K.\) The value of \(K\) is:

| 1. |
\(\dfrac{K_1d_1+K_2d_2}{d_1+d_2}\) |
2. |
\(\dfrac{K_1d_1+K_2d_2}{K_1+K_2}\) |
| 3. |
\(\dfrac{K_1K_2(d_1+d_2)}{K_1d_2+K_2d_1}\) |
4. |
\(\dfrac{2K_1K_2}{K_1+K_2}\) |