1. Ebonie Rowell
Block-2
5/14/09

2. • 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?

3. • 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.

4. • 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.

5. • 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

6. • 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.

7. • The cloud then
becomes separated
by charges
• It becomes positively
charged at the top
and negative at the
bottom creating an
electric field.

8. • 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.

9. • 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

10. Water droplets
accumulate and
become electrically
charged
Cloud becomes
The charge from
negatively and
the cloud is seen
positively
as a lightning bolt
charged
Plasma conducts An electric field
electricity and forms causing
forms the easiest plasma to be
path to the ground created