12.5 - The Story of Lightning

Lightning is a natural electrical discharge that occurs during thunderstorms. It is a striking phenomenon of nature that involves a sudden release of energy in the atmosphere. This release of energy produces a flash of light, which we see as lightning, accompanied by a thunderclap due to the rapid expansion of air around the path of the lightning.

The formation of lightning is closely related to the process of static electricity. During a thunderstorm, there is a build-up of electrical charges in clouds. The cloud is divided into different regions with positive and negative charges. The upper part of the cloud becomes positively charged, while the lower part becomes negatively charged. This difference in charge leads to the formation of an electric field between the cloud and the ground, and between different regions within the cloud itself.

When the difference in charges becomes very large, it causes the air to ionize, creating a pathway for the discharge of electricity. This discharge of electrical energy is what we observe as lightning. Lightning can occur between clouds, between a cloud and the ground, or between different regions within the same cloud.

Lightning strikes are extremely powerful. The temperature of the lightning bolt can reach up to 30,000 Kelvin, which is five times hotter than the surface of the sun. The intense heat from the lightning bolt causes the surrounding air to expand rapidly, producing the characteristic sound wave we hear as thunder.

Process of Lightning Formation

The process of lightning formation involves the following steps:

1. Charge Separation: Inside a thundercloud, strong updrafts and downdrafts cause the collision of ice particles, which leads to the separation of electric charges. The lighter, positively charged particles move to the top of the cloud, while the heavier, negatively charged particles settle at the bottom.
2. Electric Field Build-up: As the cloud accumulates charge, an electric field develops between the cloud and the Earth's surface. The stronger the charge, the stronger the electric field.
3. Breakdown of Air: When the electric field strength becomes too great, the air, which is normally an insulator, breaks down and ionizes. This allows the flow of electric current through the air, leading to lightning.
4. Discharge of Lightning: Once the air is ionized, a bolt of lightning travels through the ionized path, discharging the accumulated energy. The lightning travels in a jagged, branched path to the ground.

Electric Potential and Lightning

The electric potential of the cloud and the Earth can be measured. The voltage between the cloud and the ground can be as high as several hundred million volts. The electric field strength can be given by the formula:

$E = \frac{V}{d}$

Where:

• $E$ is the electric field strength,
• $V$ is the potential difference (voltage) between the cloud and the ground,
• $d$ is the distance between the two.

Lightning and Thunder

Thunder is caused by the rapid expansion of the air surrounding the lightning bolt due to the intense heat. This rapid expansion creates sound waves, which we hear as thunder. The speed of light is much faster than the speed of sound, so we see the lightning before we hear the thunder. The time difference between seeing the lightning and hearing the thunder can be used to estimate the distance of the lightning strike from the observer. For every 5 seconds between the flash of lightning and the thunder, the lightning is approximately 1.6 kilometers away.