Question

When dielectric medium is placed between plates of capacitor, the capacitance?

• A. Increased
• B. Decreased
• C. Remains same
• D. None of these

Answer 1

Answer:

A. Increased

Capacitance and Dielectric Media

• Fundamental Principle: When a dielectric material (an insulator like glass, mica, or paper) is inserted between the plates of a capacitor, the capacitance increases.

• Mathematical Relation: The formula for capacitance with a dielectric is C = kε₀A/d, where k is the dielectric constant (relative permittivity) of the material.

• Mechanism: The dielectric medium undergoes polarization in the presence of an electric field. This polarization creates an internal electric field that opposes the external field applied by the capacitor plates.

• Voltage Reduction: Because the net electric field between the plates decreases, the potential difference (voltage) V between the plates also decreases for a fixed charge Q. Since C = Q/V, if V decreases while Q remains constant, the capacitance C must increase.

• Dielectric Constant (k): For a vacuum, k = 1. For all other dielectric materials, k > 1, meaning the capacitance will always be greater than that of an air-gap capacitor.