In a parallel-plate capacitor of capacitance $C$, a metal sheet is inserted between the plates, parallel to them. The thickness of the sheet is half of the separation between the plates. The capacitance now becomes

The plates of parallel plate capacitor are charged upto $100 \mathrm{V}$. A $2 \mathrm{mm}$ thick plate is inserted between the plates. Then to maintain the same potential difference, the distance between the plates is increased by $1.6 \mathrm{mm}$. The dielectric constant of the plate is 

A dielectric slab of thickness $d$ is inserted in a parallel plate capacitor whose negative plate is at $X=0$ and the positive plate is at $X=3d.$ The slab is equidistant from the plates. The capacitor is given some charge. As $X$ goes from $0$ to $3d$ then,

$\left[a\right]$ The electric potential increases at first, then decreases and again increases.
$\left[b\right]$ The electric potential increases continuously.
$\left[c\right]$ The direction of the electric field remains the same
$\left[d\right]$ The magnitude of the electric field remains the same