A dielectric substance is:

• A. A device for storing an electrical charge
• B. A substance which is a good conductor of electricity
• C. An electrolyte
• D. An insulating substance allowing electrostatic induction across it

Answer: (D)

A dielectric is an insulating material that becomes polarized when placed in an electric field. This polarization is electrostatic induction: the external field causes slight shifts in the charges within the molecules, producing bound surface charges that oppose the field. Because it doesn’t conduct, it blocks current flow, but it supports an electric field across it. This allows devices like capacitors to store more charge for a given voltage, since inserting a dielectric increases the capacitance. The other descriptions refer to a device that stores charge, a good conductor, or an electrolyte, none of which capture the insulating nature and polarization behavior of a dielectric.