(g) From working the speed of sound problems above you may see a relationship that makes it easy to estimate how far away you are from a visible lightning flash. These approximations are close enough. 5seconds=1mile3seconds=1kilometer Count the seconds and estimate the distance. For example: 7 seconds =57=152=1.4mi.37=231=2.33km4seconds=54=.8mi.34=131=1.33km (1) 1 second (2) 11 seconds (3) 2 seconds (4) 15 seconds mi, km With a little practice while watching a clock's second hand you can easily develop the ability to count seconds accurately. Two methods that are adaptable are to verbalize: 1. One second, two seconds, three seconds, etc. 2. One thousand one, one thousand two, etc. (h) It has been said that "if you hear the thunder you don't have to fear the lightning," that particular lightning flash, that is. Explain. (i) In the United States on the average about 200 persons are killed annually by lightning, more than by tornadoes and more than by hurricanes and floods combined. Of those killed an inordinate number are golfers, farm equipment operators, and persons on small boats. Explain why these persons are apparently more vulnerable. J-3 Lightning and Thunder Lightning is an interesting phenomenon of thunderstorms. It is not fully understood. It may be that some combination of the violent splitting apart of millions of raindrops by updrafts and the friction of colliding ice particles of slightly different temperatures causes unequal positive and negative charges to concentrate in parts of the cloud. There is a tendency for positive charges to be concentrated at the top of the thunderstorm and negative charges in the mid levels. At the base of the cloud there are both charges present but negative dominates. The sudden balancing out of these charges, called a discharge, is what we see as lightning. The discharge is often within a cloud, but it may be between clouds, between a cloud and the ground surface, or even from a cloud into the air. It happens very quickly. Our eyes generally perceive a single lightning flash, but usually there are four or five strokes and not infrequently more than 20. Do not confuse the two terms, lightning flash vs. lightning stroke. An individual stroke may last less than .0001 second, with a longer interval but still very brief periods between strokes. A perceived flash may last from about . I second to almost a second on occasions where a flash may contain up to 40 strokes. In the latter case it might appear as fastflickering. In a typical lighting stroke between a cloud and the ground, the process seems to be this. The negative charge in the cloud reaches sufficient concentration to create an electrical field strong enough to initiate a discharge. The exchange is started by a rush of negative charges moving from the cloud toward the ground in a series of rapid stop and start surges. It is called a stepped leader because of the brief pauses, and apparently it is seeking a favorable path to the positive charge .

1. (g) From working the speed of sound problems above you may see a relationship that makes it
easy to estimate how far away you are from a visible lightning flash. These approximations are
close enough. 5seconds=1mile3seconds=1kilometer Count the seconds and estimate the distance.
For example: 7 seconds =57=152=1.4mi.37=231=2.33km4seconds=54=.8mi.34=131=1.33km
(1) 1 second (2) 11 seconds (3) 2 seconds (4) 15 seconds mi, km With a little practice while
watching a clock's second hand you can easily develop the ability to count seconds accurately.
Two methods that are adaptable are to verbalize: 1. One second, two seconds, three seconds, etc.
2. One thousand one, one thousand two, etc. (h) It has been said that "if you hear the thunder you
don't have to fear the lightning," that particular lightning flash, that is. Explain. (i) In the United
States on the average about 200 persons are killed annually by lightning, more than by tornadoes
and more than by hurricanes and floods combined. Of those killed an inordinate number are
golfers, farm equipment operators, and persons on small boats. Explain why these persons are
apparently more vulnerable.
J-3 Lightning and Thunder Lightning is an interesting phenomenon of thunderstorms. It is not
fully understood. It may be that some combination of the violent splitting apart of millions of
raindrops by updrafts and the friction of colliding ice particles of slightly different temperatures
causes unequal positive and negative charges to concentrate in parts of the cloud. There is a
tendency for positive charges to be concentrated at the top of the thunderstorm and negative
charges in the mid levels. At the base of the cloud there are both charges present but negative
dominates. The sudden balancing out of these charges, called a discharge, is what we see as
lightning. The discharge is often within a cloud, but it may be between clouds, between a cloud
and the ground surface, or even from a cloud into the air. It happens very quickly. Our eyes
generally perceive a single lightning flash, but usually there are four or five strokes and not
infrequently more than 20. Do not confuse the two terms, lightning flash vs. lightning stroke. An
individual stroke may last less than .0001 second, with a longer interval but still very brief
periods between strokes. A perceived flash may last from about . I second to almost a second on
occasions where a flash may contain up to 40 strokes. In the latter case it might appear as
fastflickering. In a typical lighting stroke between a cloud and the ground, the process seems to
be this. The negative charge in the cloud reaches sufficient concentration to create an electrical
field strong enough to initiate a discharge. The exchange is started by a rush of negative charges
moving from the cloud toward the ground in a series of rapid stop and start surges. It is called a
stepped leader because of the brief pauses, and apparently it is seeking a favorable path to the
positive charge on the ground. It is very swift, taking perhaps only about .02 second to traverse

2. the distance from the base of the cloud. It is only faintly luminous, usually invisible, and does not
compare with the brilliant return stroke that is about to occur. From nearby high points on the
surface, such as a tall tree, pole, roof top, hilltop, etc., a rush of positive charges moves up to
intercept the stepped leader and establishes a short circuit between the cloud and the ground.
Once the circuit is made, there is a huge pulse of negative charges downward to the ground,
draining negative charges from higher and higher portions of the cloud. This generates the
brilliant return stroke that we see and appears to move upward from the ground to the cloud. This
is somewhat of a misnomer, however. The return stroke is actually the rush of negative electrons
moving down to the earth, but the pulse starts low in the cloud and is quickly fed by more and
more negative charges from higher and higher in the cloud, giving an illusion of the stroke
moving upward. It is usually too quick for the eye to discern anyway. The stroke follows the
characteristically irregular path initiated by the stepped leader. As stated, the socalled return
stroke is what we see, and a single stroke lasts usually less than .0001 second. In that short burst,
however, there is an incredible flow of electrical energy, often exceeding 20,000 amperes (A)
and even 100,000A. The typical house electric circuit carries less than 30A. Rarely is there just a
single stroke, usually four or more. Immediately after the return stroke, there is another faint
leader from the cloud, this time called a dart leader, following the same channel downward as the
original stepped leader but somewhat less jagged. Again it is all but invisible. There is a bright
return stroke, another dart leader and another return stroke, and so on. And all of this we see as a
single lightning flash perhaps seeming to flicker. Because the positive charge concentration on
the ground tends to peak on high points, it is unadvisable to get under an isolated tree in a
thunderstorm, or certainly not under the tallest tree in a grove, nor on a hilltop. Lightning rods
are placed on buildings to protect them from lightning. They should be pointed metal rods ex-
Name Date Sectise tending higher than the roofline. Fither the rod ituelf or an attached hravy
miktal sire is staked into the ground. Hopefully the lightning will srike the high point on the rod
and follow the metal dona so be harralessly dissipated into the ground. Do aot be sanding nearby
barefoot on wet grosnd, of aith shoes on for that inatter: A common misconception is heur
lightning. There is no soch thing. If as regulat lightning whose source is so distant that the
lightning flash itself cannot be seea nor the thander heard. Is is aveally obsened as a brief
diffused luminosity near the horizon on bot sairimer evenings when sies evertical are clear.
Someone elie over there is seeing the flash and hearing the thander. So-called sheet lightaing is
another misconcepticen. It also is regular lughtning, ugally within a single cloud, which blocks
the visible detection of the flasth. It may or may aos be of much distanes as not to be beard. Its
appearance is genenally a sudden illumination of a clood or portioes thetcof. On some elear
evenings it is possible to see tops of distant thunderstom cumulonimbur cloads periodically

3. illumieated from within tike a giant frosted light bulh. Accompanying lightning, of course, is
thunder. The channel of a lighening stroke is only a few centimeters in diameter, perhaps about
10cm (4 inches). But the air in that chanet is beated in mieroseconds to as much as
30,000C(54,000 F). The heated air explosively expands as a shock wave which moves outward
in all directions. As the wave moves away from the source, it resembles an ordinary sound wave,
what we hear as thunder, losing force and dissipating with distance. At sea level, sound travels at
a speed of about 335m/kec. or 335km/kcc. (1100 fthec. or. 208mithec ). We can use these nates
to make some interesting calculations. Sound waves are slower than what most people as. sume.
Light on the other hand, travels at 300,000km/sec,(186,000 mines. almost one million times the
speed of sound. For all practical parposes, therefore, here on earth light is instantaneous. If you
can see the lightning flash, count the seconds before you hear the thunder and you can make a
good estimate of the distance to the lightning. A sharp loud crack of thunder secmingly
simaltancout with the lightuing flash indicates closeness. And lightning is often closer than
people would like to think. The lower frequency rolling and rumbling sounds are a result of
thunder traveling from various distances and reverberating off of the clouds. The duration of
thunder depends on several factors. The same lighting fash doen not deliver the sume. thunder to
all who experience it. Probably most important overall to the duration of thunder is the length of
the flash channel. But for the individual person that hears the thander the pervoa's location and
orientation to the channel will be the principal determinants. Because of the speed of the current
through the channel, the emanation of thunder from-all segments of the channel can be thought
of as being simultaneous. If the channel is long and you are near the terminus of the stroke, you
will hear the thunder from the terminas almost immediately bat it will take time for the thunder
that emanated from farther up the channel to reach you. Thus you hear the stretched out
rumbling, Plas. the longer the channel the more likely you are to hear reverberations of the soand
as they reflect off of other clouds and even hills and berildings. The actual sound duration from a
short segment of the lightning channel, if you want to think of it that way, say of abour 6m ( 20
feet) of channel, is less than . 1 second, in other words the duration of thunder at its source is less
than one tenth of a second, but because it must travel varied distances to the listener it may last.
several seconds, its source being all along the channel. Sometimes in a highly charged
thanderstorm with many discharges the thunder seems almost continuous. It should be mentioned
that thunder is not always heard, even though you may see the lightning. There are several
factors. Firs, the sound wave spreads in all directions and is attenuated with distance. Even under
good conditions thunder is rarely heard over 20km (12 miles). But even closer lightning
sometimes does not bring the expected thunder. Sound waves move faster in warmer air than
cooler air. The warm air on the surface and cooler air aloft cause the sound waves to bend
upward and under the right cenditions the sound may not be audible where you are. At times,

4. complex interaction of sound waves and air molecules attenuate sound waves even more, such as
in turbulent air when the presence of numerous small eddies have enhanced attenuating effect.
Figure J-3 shows persons who experience lightning and thunder from different positions in
relation to the lightning channel. Distances are given in a combination of metric and traditional
units.
(g) From working the speed of sound problems above you may see a relationship that makes it
easy to estimate how far away you are from a visible lightning flash. These approximations are
close enough. 5seconds=1mile3seconds=1kilometer Count the seconds and estimate the distance.
For example: 7 seconds =57=152=1.4mi.37=231=2.33km4seconds=54=.8mi.34=131=1.33km
(1) 1 second (2) 11 seconds (3) 2 seconds (4) 15 seconds mi, km With a little practice while
watching a clock's second hand you can easily develop the ability to count seconds accurately.
Two methods that are adaptable are to verbalize: 1. One second, two seconds, three seconds, etc.
2. One thousand one, one thousand two, etc. (h) It has been said that "if you hear the thunder you
don't have to fear the lightning," that particular lightning flash, that is. Explain. (i) In the United
States on the average about 200 persons are killed annually by lightning, more than by tornadoes
and more than by hurricanes and floods combined. Of those killed an inordinate number are
golfers, farm equipment operators, and persons on small boats. Explain why these persons are
apparently more vulnerable.