Two identical condenser M and N are connected in series with a battery. The space between the plates of M is completely filled with a dielectric medium of dielectric constant 8 and a copper plate of thickness $\large\frac{d}{2}$ is introduced between the plates of N. (d is the distance between the plates). Then potential differences across M and N are, respectively , in the ratio:

Question

$$\begin {array} {1 1} (a)\;1:4 & \quad (b)\;4:1 \\ (c)\;3:8 & \quad (d)\;1:6 \end {array}$$