The unit for dielectric strength is ____________

Question

Examoogle · Accepted Answer

$MV/m$

Explanation: Dielectric strength, also known as the breakdown strength of an insulating material, is defined as the maximum electric field strength that a material can withstand without experiencing electrical breakdown. It is the ratio of the breakdown voltage to the thickness of the insulation, hence its unit is Volts per meter (V/m), commonly expressed as MV/m for engineering convenience.

Working Principle: When an insulating material is placed in an electric field, the material experiences stress. As the potential difference increases, the electric field intensity ($E = \frac{V}{d}$) increases. Once the electric field exceeds the dielectric strength of the material, the molecular bonds within the dielectric rupture, causing a transition from insulator to conductor through electron avalanche or thermal breakdown.

Key Formulas: $E_d = \frac{V_{bd}}{d}$ — where $E_d$ is dielectric strength, $V_{bd}$ is breakdown voltage, and $d$ is the thickness.

Key Points: Dielectric strength represents the insulating quality of a material.; Higher dielectric strength allows for thinner insulation in electrical components.; It is temperature and humidity dependent.; Common unit is MV/m or kV/mm.

Advantages: Allows for miniaturization of high-voltage equipment.; Essential for designing safe electrical insulation systems.

Disadvantages: Degrades over time due to thermal stress and partial discharge.; Affected significantly by the presence of impurities or moisture.

Applications: High voltage cable insulation.; Transformer oil testing.; Capacitor design.

Additional Info: For air at standard pressure and temperature, the dielectric strength is approximately 3 MV/m.. Option A (V/m^2) incorrectly implies a surface charge density unit.. Option B (MV/m^2) is dimensionally incorrect for electric field intensity.

Answer: C is correct — The unit for dielectric strength is Volts per meter ($V/m$), which is commonly represented as Megavolts per meter ($MV/m$).

Exam Tip: Remember that Dielectric Strength is essentially a measure of Electric Field Intensity ($E = V/d$), so it always carries units of potential divided by distance.

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