Basic classification: What must a dielectric material be? In the context of electrostatics and AC insulation, a dielectric is a material that can be polarized but does not allow appreciable DC conduction. Which option best describes what a dielectric must be for practical purposes?

Introduction / Context:
Dielectrics are used to separate conductors, store electric energy in capacitors, and guide fields in cables. Their essential property is high electrical resistance along with the ability to become polarized in an electric field, thereby increasing capacitance without significant leakage.

Given Data / Assumptions:

• Working voltages can be DC or AC.
• Desired features: high breakdown strength, low leakage, low dielectric loss.
• Examples: ceramics, polymers (PTFE, XLPE), glass, mica.

Concept / Approach:

A dielectric must be an electrical insulator (very low DC conductivity). When an electric field is applied, bound charges displace slightly, creating polarization and enabling energy storage without free-charge conduction. Conductors would short the field; semiconductors would leak significantly; a generic “resistor” description is too broad and does not capture polarization behavior.

Step-by-Step Solution:

Verification / Alternative check:

Capacitor models use ideal C with very large parallel resistance; materials specified as dielectrics exhibit breakdown strengths in kV/mm and very low leakage currents.

Why Other Options Are Wrong:

Conductors allow free charge flow; “resistor” is non-specific; semiconductors conduct appreciably; superconductors exhibit zero resistance and are not dielectrics.

Common Pitfalls:

Assuming any high-resistance material is a suitable dielectric without considering breakdown and loss tangent.

Final Answer:

insulator