Electrical insulator that can store electric energy.

• A. Dielectric
• B. Conductor
• C. Insulator
• D. Semiconductor

Answer: (A)

The key idea is that energy can be stored in the electric field of a material that stays insulating. A dielectric is exactly that: an insulating material that becomes polarized when an electric field is applied. This polarization creates bound charges inside the material, allowing the field energy to be stored—crucial for devices like capacitors. The energy density in a dielectric scales with its permittivity and the square of the field (u = 1/2 ε E^2), so using a dielectric increases how much energy can be stored at a given voltage. A conductor would not store this field energy in the same way because free charges move to cancel the field inside, so the energy isn’t stored in the material. A general insulator doesn’t guarantee the polarization needed for energy storage, and a semiconductor’s partial conductivity isn’t suited for storing field energy like a dielectric does. Hence, the best term for an insulating material that can store electric energy is dielectric.