The gap between the plates of a parallel plate capacitor of area \(A\) and distance between plates \(d\), is filled with a dielectric whose permittivity varies linearly from \({ \varepsilon _1}\) at one plate to \({ \varepsilon _2}\) at the other. The capacitance of capacitor is

1. A \({ \varepsilon _0}\left( {{ \varepsilon _1} + { \varepsilon _2}} \right)A/d\)
2. B \({ \varepsilon _0}\left( {{ \varepsilon _2} + { \varepsilon _1}} \right)A/2d\)
3. C \({ \varepsilon _0}\,A/\left[ {d\,\ln \left( {{ \varepsilon _2}/{ \varepsilon _1}} \right)} \right]\)
4. D \({ \varepsilon _0}\left( {{ \varepsilon _2} - { \varepsilon _1}} \right)A/\left[ {d\,\ln \left( {{ \varepsilon _2}/{ \varepsilon _1}} \right)} \right]\)