Lightning A cloud has a large positive charge. Assume that...

Name: Problem 4, Chapter 14: College Physics
Uploaded: 2020-05-19T04:29:56-08:00
Duration: 1 min
Channel: Dading Chen
Description: Lightning A cloud has a large positive charge. Assume that this is the only cloud in the sky over Earth and that Earth is a good electrical conductor. Draw a sketch showing electric charge distribution on Earth due to the cloud’s electric charge. Explain why a person’s hair might stand on end before a lightning strike.

Lightning A cloud has a large positive charge. Assume that this is the only cloud in the sky over Earth and that Earth is a good electrical conductor. Draw a sketch showing electric charge distribution on Earth due to the cloud’s electric charge. Explain why a person’s hair might stand on end before a lightning strike.

Key Concepts

Electrostatic Induction

When a charged object, such as a positively charged cloud, is near a conductor, it causes a redistribution of charges within the conductor without the conductor itself gaining a net charge. In this case, the Earth, being a good conductor, will have electrons drawn toward the region directly below the cloud, creating a negatively charged area there, while any surplus positive charge is repelled to regions farther away.

Conductors and Charge Distribution

Conductors allow free movement of electrons, meaning that when an external electric field is applied, as from a charged cloud, the electrons in the Earth move to balance the induced forces. This results in a non-uniform distribution of charge, with regions of negative charge directly under the positively charged cloud and relative positive charge in other areas. This concept is critical in understanding phenomena such as lightning, where such charge separations lead eventually to electrical discharges.

Electric Field Effects on Polarizable Matter

As the cloud’s electric field intensifies, it can induce charges or polarization in nearby objects, including a person’s hair. When each hair strand becomes similarly charged by accumulating like charges due to the local electric field, the strands repel each other. This mutual repulsion can cause hair to stand on end, a visible signal that a strong static electric field is present prior to a lightning strike.

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