What property of air determines its ability to withstand high voltages before breakdown between conductors?

• A. Dielectric strength
• B. Thermal conductivity
• C. Magnetic permeability
• D. Relative permittivity

Answer: (A)

Dielectric strength of air determines how much electric field the air can tolerate before it ionizes and becomes conductive, leading to breakdown between conductors. This property sets the threshold for insulation: higher dielectric strength means air can sustain a stronger electric field without forming an arc. In practical terms, air at standard conditions breaks down around a few million volts per meter, so spacing and careful design rely on this limit to prevent arcing.

Thermal conductivity isn’t about voltage breakdown; it affects how heat is moved away but not the insulating limit. Magnetic permeability relates to how a material reacts to magnetic fields, not electrical insulation between conductors. Relative permittivity tells us how a material polarizes and stores energy in an electric field, influencing capacitance, not the voltage at which air loses its insulating properties.