Accumulation of positive charges near the ground
Explanation
Lightning is a massive electrostatic discharge caused by an imbalance of electric charges between storm clouds and the ground. This phenomenon relies on the principles of triboelectricity (charging by friction) and electrostatic induction.
Detailed Analysis
The charge distribution leading to a lightning strike typically follows this sequence:
- Charge Separation in Clouds: Within a thundercloud (cumulonimbus), rising air currents and falling water droplets/ice crystals collide. This friction causes positive charges to accumulate at the top of the cloud and negative charges to accumulate at the bottom.
- Electrostatic Induction: The accumulation of negative charges at the base of the cloud creates a strong electric field. This negative charge repels electrons on the Earth's surface, pushing them deeper into the ground.
- Induced Positive Charge: As a result of this repulsion, a net positive charge accumulates on the surface of the ground, particularly concentrating on protruding objects like trees, buildings, and lightning conductors.
- Discharge: When the potential difference becomes sufficient to overcome the dielectric strength of air, current flows between the negative cloud base and the positive ground, resulting in lightning.
Therefore, the condition existing near the ground just before the strike is an accumulation of positive charges.
Key Takeaway: During a thunderstorm, the lower portion of the cloud generally becomes negatively charged, which induces an accumulation of positive charges on the ground beneath it via electrostatic induction.