Dry, clean air normally has a ______ strength of about 10,000 volts per inch. This means that you would have to apply a voltage greater than 10,000 volts across conductors separated by one inch of air to establish current flow across the separated conductors.

Dry, clean air normally has a ______ strength of about 10,000 volts per inch. This means that you would have to apply a voltage greater than 10,000 volts across conductors separated by one inch of air to establish current flow across the separated conductors.

• A. Dielectric
• B. Conductive
• C. Permittivity
• D. Resistivity

Answer: (A)

Dry air acts as an insulator, and its ability to withstand an electric field before breaking down is measured as dielectric strength. For air at standard conditions, this strength is about 10,000 volts per inch. So with a one-inch gap, you can apply up to roughly 10 kV without an electric arc forming. If the voltage exceeds that threshold, the air ionizes and becomes conductive, allowing current to flow across the gap. This concept is what the term dielectric strength is describing—the insulating capability of air. The other options don’t fit because dielectric describes the insulating nature in general, permittivity is about how a material polarizes in an electric field, resistivity is about how strongly a material resists current, and conductive refers to a material that readily allows current to pass.

Dry air acts as an insulator, and its ability to withstand an electric field before breaking down is measured as dielectric strength. For air at standard conditions, this strength is about 10,000 volts per inch. So with a one-inch gap, you can apply up to roughly 10 kV without an electric arc forming. If the voltage exceeds that threshold, the air ionizes and becomes conductive, allowing current to flow across the gap. This concept is what the term dielectric strength is describing—the insulating capability of air. The other options don’t fit because dielectric describes the insulating nature in general, permittivity is about how a material polarizes in an electric field, resistivity is about how strongly a material resists current, and conductive refers to a material that readily allows current to pass.