Why is the thunder longer than the flash?

Question

Why does the sound of thunder take so much longer to stop than the flash, which we see only a split second?

(note: I'm not asking why the thunder arrives later)

Answer 1

sythyril has the best of the answers so far. You can learn a lot from the reference about how lightning works.

Most lightning flashes occur in less than 1 second. Light is produced during the entire duration of the electric discharge. Light from the nearest and farthest points of discharge reach you within microsends of each other. Reflections may take a few more microseconds. Even if your eye and brain could detect this delay, they would expect the differences based on where the light is coming from.

The sound is produced for a longer time. By the time the discharge is finished, the air is still expanding and water droplets are still boiling. As this effect subsides, you get more sound from the secondary effect, the air cooling, the steam condensing, and the atmosphere collapsing back in on the discharge column. A large lightning strike makes sound for several seconds.

The sound takes many more different paths to reach you. The speed of sound varies with air temperature. Wind can raise or lower it. The variation here is seconds, not microseconds. Because sound has a much much longer wavelength than light, stereoscopic hearing is much less effective than stereoscopic vision. You can't tell which sound is coming from which direction.

Answer 2

The time it takes for the sound to get to you depends on the air density due to temp 1 mile or kilometer is a very good rule of thumb. Thunder is caused by rapid heating of the air. Like a piece of red hot steel dropped in water makes. It's called the sound of thermal shock. Lightning is produced in thunderstorms when liquid and ice particles above the freezing level collide, and build up large electrical fields in the clouds. Once these electric fields become large enough, a giant "spark" occurs between them, like static electricity, reducing the charge separation. The lightning spark can occur between clouds, between the cloud and air, or between the cloud and ground. Cloud-to-ground lightning usually occurs near the boundary between the updraft region (where the darkest) clouds are, and the downdraft/raining region (with the lighter, fuzzy appearance). Sometimes, however, the lightning bolt can come out of the side of the storm, and strike a location miles away, seemingly coming out of the clear blue sky. As long as a thunderstorm continues to produce lightning, you know that the storm still has active updrafts and is still producing precipitation. The temperature inside a lightning bolt can reach 50,000 degrees F . Objects that are struck by lightning can catch on fire, or show little or no evidence of burning at all.

Answer 3

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.

Dr. H

Answer 4

For starters sound travels alot slower then light ( look at any basic high school physics book) Then some people would argue about this being redone it the rate of change of the matter involved. Hot air colliding with cold for the thunder and a unbalance of the charges that causes the lighting.

Answer 5

Because there are two very different phenomena involved.

The light you see is an emission as air molecules are ionized (i.e., stripped of electrons) As such it lasts only as long as the current is flowing.

The sound you hear is from air rushing in to fill the reduction of air volume within the former body of the bolt. As this air rushes in from from every side it collides and produces sound. This situation takes a little while to reach equilibrium as it is quite chaotic, which is why thunder lasts longer.

Answer 6

Echoes, mostly. If you're very close to a lightning strike the sound is incredibly loud but very brief in duration.

Thunder also lasts slightly longer due to reverberations in the hot air near the path of the lightning after the lightning is gone, but this effect only lasts for a few hundredths of a second. It's mostly echo.

Answer 7

All of sound travels at a lower frequency than light. Because sound uses a much lower frequency it must take longer to transmit or receive a bit of information than say light.

What is the information in this case? That lightning just struck. You have two methods of gathering the information through light or through sound.

This is why everyone wants fiber optics to the home, because light has a higher frequency and can transmit much more information per unit of time than say the electrical signals in copper.

This is why FM comes in stero and why AM doesn't because FM transmits at a higher frequency and can transmit much more information (2 channels).

I hope this makes sense...

Answer 8

because a lightning stroke can be several miles long, the sound from the closest part will reach you sooner than the sound from the further part.

Roughly 5 seconds for each mile.

Yes, echoes also play a part.

Answer 9

The sound of thunder is from lightning discharges .. one bang from each discharge... they reverberate among the clouds giving rise to the long, rolling sound....Notice that it diminishes as it echoes from clouds further away.

Answer 10

b/c light travels faster, if a fast car goes past you and a turtle goes past you, you see the turtle a longer amount of time . also light doesnt echo