©2004 IUPUI, all rights reserved. Written by Andrew Gavrin and Gregor Novak, Indiana University-Purdue
University-Indiana. Used by permission.
good for understanding and dealing with the world around us.
It allows us to see the underlying connections among different
phenomena, and to make predictions about them. In many cases
(volcanoes, floods, etc.) accurate predictions may improve our
lives or even save them. In the case of lightning, annual costs
in the U.S. alone are approximately 200 dead, hundreds more
injured, and over $2 billion in property damage.
More people in the U.S. are killed by lightning than by
floods, tornadoes, or hurricanes.
|Thanks to NASA for this
In this course we will study many topics, but almost all of
them have something to do with electricity. Lightning is the most
dramatic example of electricity at work in nature. Research on
lightning goes back at least as far as the work of Benjamin
Franklin, who demonstrated the connection between
electricity and lightning with his famous (and dangerous) kite
Lightning occurs when an electrical current flows between
the Earth and storm clouds. Although the details are still
being researched, the basic ideas are clear. Small particles
known as hydrometeors interact within the storm cloud. These
particles transport charge within the cloud, usually carrying
positive charge to the top of the cloud and negative charge to
the bottom. This means that there will be large electric fields
within the cloud, and between the cloud and the ground. The
difference in electric potential (voltage) can be millions of
volts. Eventually, the air is unable to insulate the cloud from
the ground, and a large current results.
This brief description includes several important physical
processes that we will discuss in the course. Some are in the
current chapter, but some will come over the next few weeks.
Try to look out for them as they come up!
- Charge transfer by collisions or friction
- Electric fields and potential differences around charged
- Polarization of insulating materials by an electric
- Dielectric breakdown.
- Motion of charged particles in an electric current.
Here are a few vital statistics about lightning:
- A typical bolt is 6 miles long.
- The temperature of the ionized air that we see is over
- Typical cloud to ground voltage: few million volts.
- Peak power: 1011 to 1012 watts.
- Average duration: about 30 microseconds.
- Peak current: around 105 amps.
- Total Energy: about 107 joules.
Do not become a statistic. When
lightning threatens, follow these safety tips from the National
Oceanic and Atmospheric Administration (NOAA), U.S. Department
| Photo credit: National Renewable
Laboratory, U.S. Dept. of Energy
Nowadays, most lightning strikes in the U.S. are recorded by the
National Lightning Detection Network (NLDN), which consists of
over one hundred antennae that report to a central data
collection and processing computer. This system is run by Global Atmospherics,
- Stay indoors, and don't venture outside, unless
- Stay away from open doors and windows, fireplaces,
radiators, stoves, metal pipes, sinks, and plug-in electrical
- Don't use plug-in electrical equipment like hair driers,
electric toothbrushes, or electric razors during the
- Don't use the telephone during the storm. Lightning may
strike telephone lines outside.
- Don't take laundry off the clothesline.
- Don't work on fences, telephone or power lines,
pipelines, or structural steel fabrication.
- Don't use metal objects like fishing rods and golf clubs.
Golfers wearing cleated shoes are particularly good lightning
- Don't handle flammable materials in open containers.
- Stop tractor work, especially when the tractor is pulling
metal equipment, and dismount. Tractors and other implements
in metallic contact with the ground are often struck by
- Get out of the water and off small boats.
- Stay in your automobile if you are traveling. Automobiles
offer excellent lightning protection.
- Seek shelter in buildings. If no buildings are available,
your best protection is a cave, ditch, canyon, or under
head-high clumps of trees in open forest glades.
- When there is no shelter, avoid the highest object in the
area. If only isolated trees are nearby, your best protection
is to crouch in the open, keeping twice as far away from
isolated trees as the trees are high.
- Avoid hilltops, open spaces, wire fences, metal
clotheslines, exposed sheds, and any electrically conductive
- When you feel the electrical chargeif your hair
stands on end or your skin tingleslightning may be about
to strike you. Drop to the ground immediately.
Don't believe everything you read. I found a Web site
that included a fancy movie about how lightning works. It
included the statement "lightning occurs when a cloud
is charged with negative electrons and the ground is charged
with positive electrons."
Further study links:
The links below will take you to sites with
more detailed information.
3. 4. 5.
Further Study Questions:
For extra credit answer the following questions.