Sunday, November 07, 2004

Electricity Lesson 7

ELECTRICITY LESSON 7 - Lightning
Lesson: 7.
Take up Hwk: Lab page 59 course pack – question pg. 61
Hand back Quiz
Lightening Video and questions teachers cupboard rm 336 C.P. pg. 65 Text pg. 290-291
Overhead of lightening (intro)
Homework: Complete pg. 65 course pack

Lightning

The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels at 186,000 miles in a second, almost a million times the speed of sound. Sound travels at the slower speed of one-fifth of a mile in the same time. So the flash of lightning is seen before thunder is heard. By counting the seconds between the flash and the thunder and dividing by 5, you can estimate your distance from the strike (in miles). But why does lightning cause thunder at the same time it strikes?

Lightning causes thunder because a strike of lightning is incredibly hot. A typical bolt of lightning can immediately heat the air to between 15,000 to 60,000 degrees Fahrenheit. That's hotter than the surface of the sun!
A lightning strike can heat the air in a fraction of a second. When air is heated that quickly, it expands violently and then contracts, like an explosion that happens in the blink of an eye. It's that explosion of air that creates sound waves, which we hear and call thunder.
When lightning strikes very close by, we hear the thunder as a loud and short bang. We hear thunder from far away as a long, low rumble.
Lightning always produces thunder. When you see lightning but don't hear any thunder, the lightning is too far away from you for the sound waves to reach you.
Light and sound will always move at different speeds. And lightning will always produce thunder because of a strike's high temperature. So no matter what, you will always see a flash of lightning before you hear thunder.

Here's some more good information on lightning:
http://www.nasaexplores.com/show_912_teacher_st.php?id=030108154146

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