12.1 - Lightning

Lightning is a natural phenomenon that occurs due to the discharge of static electricity in the atmosphere. It is a sudden and powerful electrostatic discharge between two electrically charged regions, typically occurring between clouds or between a cloud and the Earth's surface.

Lightning is caused by the separation of electric charges within clouds. During a thunderstorm, rising warm air carries water droplets or ice crystals upward, while falling cool air brings down water vapor. This leads to the accumulation of positive charges at the top of the cloud and negative charges at the bottom. The Earth's surface also gets positively charged in response to the negative charge at the cloud's bottom.

As the separation of charges increases, the electric field strength between the cloud and the ground or within the cloud itself increases. When the electric field strength exceeds the insulating power of air, a discharge occurs, which is lightning. This discharge can occur in different forms, such as cloud-to-cloud, cloud-to-ground, or within a single cloud.

There are mainly three types of lightning:

• Cloud-to-ground lightning: This is the most common type of lightning where a discharge occurs between the cloud and the ground. The lightning bolt travels from the negatively charged lower part of the cloud to the positively charged surface of the Earth.
• Cloud-to-cloud lightning: This type of lightning occurs between two clouds, typically between the positively charged upper regions of one cloud and the negatively charged lower regions of another cloud.
• Intra-cloud lightning: This occurs within a single cloud, between the positive and negative regions of the cloud itself.

The electric discharge of lightning heats the surrounding air to around 30,000°C, which is five times hotter than the surface of the sun. This rapid heating of the air causes it to expand explosively, creating a shock wave that we hear as thunder.

Key Terms and Concepts:

• Lightning Strike: The actual discharge of electrical energy from the cloud to the ground or between clouds.
• Thunder: The sound caused by the sudden expansion of heated air during a lightning strike.
• Electric Field: A region around a charged object where a force would be exerted on other charged objects.
• Static Electricity: The buildup of electric charges on the surface of objects, typically due to friction.

Formula:

Lightning is often associated with the movement of electric charges and can be described in terms of the electric field $E$ between two charged objects. The strength of the electric field is given by the formula:

Electric Field: $E = \frac{F}{q}$

where $E$ is the electric field, $F$ is the force acting on a charge, and $q$ is the magnitude of the charge.

During a lightning strike, the high voltage between the charged regions of the cloud and the Earth's surface causes a breakdown of air's insulating properties, resulting in a sudden discharge. The energy released in the form of light (lightning) and sound (thunder) can be immense.

Effects of Lightning:

• Lightning can cause fires, power surges, and damage to electrical equipment.
• It can also cause injuries and fatalities, especially when it strikes people or animals.
• It plays a role in nitrogen fixation in the soil by converting nitrogen in the atmosphere into a usable form for plants.

Lightning is an important aspect of the Earth's natural processes and plays a role in maintaining the balance of the Earth's atmosphere. However, it also presents dangers, and it is important to follow safety precautions during thunderstorms.