Question

Corona discharge is caused by

• A. Ionization of gas molecules due to dielectric breakdown
• B. High charge density causing high electric fields near a metal’s surface.
• C. Charges moving into the ionized air under the effect of this electric field.
• D. All of the above

Answer 1

The correct option is D All of the above

Corona discharge takes place when there is dielectric breakdown around a conductor. The dielectric strength of air is given to be $3,000,000\frac{V}{m}$ So, if the conductor creates an electric field more than $3,000,000\frac{V}{m}$ then dielectric breakdown will take place
The electric field produced by a conductor is given by $\frac{\sigma }{{\epsilon }_0}$ where $\sigma$ is the local charge density So if
$\frac{\sigma }{{\epsilon }_0}$ increases to a value higher than the dielectric strength of air, we will have corona discharge.
These charges leak into the ionized air (which is now conducting) because of the electric field.