Theories of charge formation || EEE Dept Online Class || Bethlahem Institute of Engg || Jeksha

Summary

This lecture from Bethlehem Institute of Engineering explores the phenomenon of charge separation in clouds, a key process behind lightning. It covers three main theories: Wilson’s theory, which explains polarization of raindrops leading to lower negative and upper positive charges; Simpson’s theory, which divides clouds into three regions with varying charge distributions due to high-velocity air currents and ice crystals; and Reynolds & Mason’s theory, which refines Simpson’s model by highlighting the role of hailstones and splinters in charge distribution. The session clearly explains how ions, air currents, and freezing processes contribute to cloud electrification, culminating in lightning formation.

Takeaways

• 🌩️ Charge separation in clouds is a fundamental process that leads to phenomena like lightning.
• ⚡ Wilson's theory explains charge separation based on ions in the atmosphere and the effect of the electric field.
• 💧 In Wilson's theory, raindrops become polarized: the upper side acquires negative charge and the lower side acquires positive charge.
• 🌫️ According to Wilson, the lower part of a cloud is negatively charged, and the upper part is positively charged.
• 🌬️ Simpson's theory divides clouds into three regions (A, B, C) to explain charge distribution.
• ☁️ In Simpson's theory, Region A (lowest) is positively charged due to high-velocity air currents breaking raindrops.
• ❄️ In Simpson's theory, Region C (top) contains ice crystals that are negatively charged, while Region B is negatively charged.
• 🧊 Reynolds and Mason modified Simpson's theory to account for cloud height and temperature variations.
• 🌨️ In Reynolds and Mason's theory, hailstones in the lower cloud region carry negative charges, and splinters in the upper region carry positive charges.
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• 📊 A comparison of theories shows that both Wilson and Reynolds & Mason predict negative lower regions and positive upper regions, while Simpson's theory varies across three regions.
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• ⚡ Once charge separation is established in clouds, lightning strokes can occur.

Q & A

What is charge separation in clouds?

Charge separation in clouds refers to the process by which positive and negative charges are distributed in different regions of a cloud, leading to the formation of electric fields. This process is a crucial component of phenomena like lightning.

What are the three main theories explaining charge separation in clouds?

The three main theories explaining charge separation in clouds are Wilson's Theory, Simpson's Theory, and Reynolds and Mason's Theory.

How does Wilson's Theory explain charge separation?

Wilson's Theory suggests that atmospheric ions attach to dust and water particles. These particles become polarized in the electric field, causing the lower part of the cloud to acquire negative charges and the upper part to acquire positive charges.

What role do ions play in Wilson's Theory of charge separation?

In Wilson's Theory, ions in the atmosphere attach themselves to dust and water particles. These charged particles interact with the electric field, leading to the polarization of raindrops and charge separation within the cloud.

How does Simpson's Theory explain the charge distribution in clouds?

Simpson's Theory divides the cloud into three regions: A (lower), B (middle), and C (upper). Region A becomes positively charged due to high-velocity updrafts, Region B becomes negatively charged, and Region C is negatively charged due to ice crystals forming at temperatures below freezing.

What happens in Region A of Simpson's Theory?

In Region A of Simpson's Theory, high-velocity updrafts break raindrops, causing the positive charges to remain in the cloud. This results in Region A being positively charged.

How do air currents affect charge separation in Simpson's Theory?

In Simpson's Theory, high-velocity air currents cause the breaking of raindrops and the movement of charges within the cloud. This leads to the positive charge in Region A and negative charge in Region B. Ice crystals in Region C further contribute to charge separation.

What is the main difference between Simpson's and Wilson's Theory?

The main difference is that Simpson's Theory divides the cloud into three regions and explains charge separation through updrafts, while Wilson's Theory focuses on the role of atmospheric ions and electric fields in polarizing raindrops.

How does Reynolds and Mason's Theory modify Simpson's Theory?

Reynolds and Mason's Theory modifies Simpson's Theory by accounting for the formation of ice crystals at extremely low temperatures in the upper cloud, leading to the creation of hailstones. These hailstones carry negative charges to the lower part of the cloud, while splinters carry positive charges to the upper part.

What is the significance of hailstones in Reynolds and Mason's Theory?

In Reynolds and Mason's Theory, hailstones play a key role in charge separation by carrying negative charges to the lower part of the cloud. Their heavy mass causes them to fall, while air currents move positively charged splinters to the upper cloud region.

How does temperature affect charge separation according to Reynolds and Mason's Theory?

According to Reynolds and Mason's Theory, temperature plays a critical role in charge separation. Water droplets freeze at temperatures below -40°C, forming ice crystals (hailstones) that carry negative charges to the lower region, while the upper region retains positive charges due to splinters.

What is the final charge distribution according to Reynolds and Mason's Theory?

According to Reynolds and Mason's Theory, the lower region of the cloud consists of negative charges due to hailstones, while the upper region consists of positive charges due to splinters carried by air currents.

How does charge separation contribute to the formation of lightning?

Charge separation within clouds leads to an imbalance of charges between the cloud and the Earth’s surface, which can eventually discharge in the form of a lightning stroke, neutralizing the charge difference.