A dielectric is basically a ________.

Question

Examoogle · Accepted Answer

insulator

Explanation: A dielectric is an electrical insulator that can be polarized by an applied electric field. When placed in an electric field, electric charges do not flow through the material as they would in a conductor, but only slightly shift from their average equilibrium positions, causing dielectric polarization.

Working Principle: In a dielectric, all electrons are tightly bound to the nucleus, preventing continuous current flow. Upon application of an external electric field $E$, the positive and negative charges undergo small displacements, creating internal electric dipoles. This polarization creates an internal field $E_i$ that opposes the external field, effectively reducing the net electric field within the material.

Key Formulas: $P = \chi_e \epsilon_0 E$ — Electric polarization $P$ in terms of electric susceptibility $\chi_e$ and field $E$; $\epsilon = \epsilon_0 \epsilon_r$ — Relation between absolute permittivity $\epsilon$, vacuum permittivity $\epsilon_0$, and relative permittivity $\epsilon_r$

Key Points: Dielectrics have a wide band gap between the valence and conduction bands.; They are primarily used to store energy in capacitors by increasing capacitance.; They do not conduct electricity because they lack free charge carriers.; The quality of a dielectric is often characterized by its dielectric strength (kV/mm).

Advantages: Reduces the intensity of the electric field within the material.; Prevents arcing or breakdown at high voltages when used as insulation.

Disadvantages: Subject to dielectric breakdown if the electric field exceeds the material's threshold.; Dielectric loss (heating) occurs in AC circuits due to dipole relaxation.

Applications: Insulating materials in power transformers and cables.; Dielectric medium in capacitors to increase charge storage capacity.

Additional Info: Common dielectric materials include mica, glass, ceramics, and polymers like polyethylene.. Option A is incorrect because a capacitor uses a dielectric to store charge, but it is a device, not the material itself. Option B is incorrect as conductors allow flow of charges. Option D is incorrect because semiconductors exhibit conductive properties based on external factors.

Answer: C is correct — A dielectric is fundamentally an electrical insulator capable of becoming polarized when exposed to an electric field.

Exam Tip: Always remember that while all dielectrics are insulators, not all insulators are optimized for use as dielectrics in capacitor applications, where high permittivity is prioritized.

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