Question

Dielectrics play an important role in design of capacitors. The molecules of a dielectric may be polar or non-polar. When a dielectric slab is placed in an external electric field, opposite charges appear on the two surfaces of the slab perpendicular to electric field. Due to this an electric field is established inside the dielectric. The capacitance of a capacitor is determined by the dielectric constant of the material that fills the space between the plates. Consequently, the energy storage capacity of a capacitor is also affected. Like resistors, capacitors can also be arranged in series and/or parallel.

A 100 μF capacitor is charged by a 12 V battery.

A capacitor of capacitance 4 μF is charged to a potential difference of 100 V. The energy stored in the capacitor is:

Read the following statements about a parallel-plate capacitor and identify the correct option: (I) The capacitance of a parallel-plate capacitor in vacuum is given by C = ε0A/d, where A is the area of each plate and d is the separation between them. (II) When a dielectric slab of dielectric constant K is fully inserted between the plates, the capacitance becomes K times its earlier value. (III) The energy stored per unit volume (energy density) in the electric field between the plates (in vacuum) is u = ½ ε0E². (IV) If the plates of an isolated charged capacitor are pulled farther apart at constant charge, the energy stored in the capacitor decreases.