Ebonie RowellBlock-25/14/09

• What is that bright flash of light that shoots across the sky during a storm?

• It’s lightning, and it’s an enormous electrical discharge that occurs in the atmosphere during thunderstorms.

• But what exactly causes this electricity in the sky?

LIGHTNING

• The first study of lightning occurred in the 18th century by Benjamin Franklin

• He theorized that clouds are electrically charged and, therefore, lightning must be electrical in nature

• He tied a key to a damp kite string, which was then tied to an insulating silk ribbon wrapped around his hand. Sparks were observed to be jumping from the key .

• Franklin’s hypothesis was proved correct.

History of Lightning

• In the process of the water cycle, moisture can accumulate in the atmosphere. This accumulation is what we see as a cloud

• Cloud droplets collide other moisture that is in the process of condensing as it rises.

STEP 1

• The importance of these collisions is that electrons are knocked off of the rising moisture

• The newly knocked-off electrons gather at the lower portion of the cloud, giving it a negative charge

Step 2

• As the rising moisture encounters colder temperatures in the upper cloud regions and begins to freeze, the frozen portion becomes negatively charged and the unfrozen droplets become positively charged.

• Here, rising air currents have the ability to remove the positively charged droplets from the ice and carry them to the top of the cloud.

• The cloud then becomes separated by charges

• It becomes positively charged at the top and negative at the bottom creating an electric field.

STEP 4

• The electric field becomes so large, it can rip some of the electrons of the air molecules, you then get some electrons and positive ions - a plasma.

• As there are free electrons and positive ions, this plasma conducts electricity very well unlike air which is a good insulator, and electricity will follow the easiest path, so all the charge from a significant portion of a cloud will follow this path, creating a huge spark - a lightning bolt.

• The entire process of a lightning bolt occurs in a matter of seconds

Water droplets accumulate and

become electrically charged

Cloud becomes negatively and

positively charged

An electric field forms causing

plasma to be created

Plasma conducts electricity and forms the easiest path to

the ground

The charge from the cloud is seen as a lightning bolt

THE BREAKDOWN