Why do you see lightning first and then hear thunder

In summer, thunder and lightning are common, and thunder is heard only a few seconds to a dozen seconds after the lightning has passed.

Lightning is an electrical spark produced when the charge generated by the cloud during its motion is discharged when it is discharged, and it is both light and sound. It's just that the light and sound in thunder and lightning are more powerful than the electric sparks we see in our lives.

The reason why lightning is seen first and then thunder is heard is because in the air, light travels fast and reaches the ground quickly, while sound travels slowly in the air and reaches the earth after a while. So you will hear the lightning first and then hear the thunder. In fact, lightning and thunder appear at the same time.

The reason for such a difference in the time it takes to reach the ground is that light travels 3,000,000 kilometers per second, while sound travels only one kilometer in the air. The speed of sound is only one-900,000th the speed of light.

Some lightning bolts are long, some are short, some are loud, and some are quiet. You can roughly judge the height of the clouds to the ground based on the time it takes for the sound to reach the ground. It doesn't take much time for the light to reach the ground, it can be considered 0, from seeing lightning to hearing thunder, how many seconds is the interval and multiplied by 340 meters, which is the distance from lightning to you.

Thunder is reflected when it encounters clouds or tall buildings, so it usually takes a while for a lightning bolt to disappear.

In fact, in thunderclouds, lightning and thunder occur at the same time, and the reason why people always see lightning first and hear thunder later is because light travels much faster than sound.

Light travels almost 300,000 kilometers per second in the air, and at such a speed, it can travel seven and a half times around the Earth's equator in one second. Sound travels about 340 meters per second in the air, almost 1/900,000 of the speed of light.

The time it takes for light to travel from the place where the lightning occurs to the ground is usually only a few hundredths of a second, but it takes a long time for the sound to travel the same distance.

According to this common sense, one can judge the time difference between seeing lightning and hearing thunder. Calculate how far the discharge is from the ground.

Because in the air, light travels fast and reaches the ground very quickly, while sound travels slowly in the air and only reaches the earth after a while. So you will hear the lightning first and then hear the thunder.

In fact, lightning and thunder occur almost simultaneously. However, lightning is light, and the speed of light in the air is about 300,000 kilometers per second, while thunder is sound, and the speed of sound is about 340 meters per second, and the speed of light is nearly 900,000 times the speed of sound travel.

It takes almost no time for lightning to reach the ground, which is negligible, but it takes a certain amount of time for sound to travel from the clouds to the ground. Because of this, although lightning and thunder occur at the same time, we always see lightning first, and only after a while, we hear thunder.

Principle explanation: the speed of light propagation is faster than the propagation speed of sound, the closer a person is to lightning, then the shorter the time between seeing lightning and hearing lightning; The farther away from the lightning, the light will be a long distance away from the sound, and when you see the lightning, that is, the light is coming to you, the sound is still behind, and it will take a while to hear it.

For example, two people are racing at the speed, you are at the finish line, they are riding a bicycle alone, representing the light of lightning, and walking alone, representing the sound of lightning, both moving towards the finish line at a fixed speed, the farther the end point is from the starting point, the farther away the bicycle and the person walking, and the first to reach the finish line is the bicycle, that is, the first to see the lightning.

Formation of thunder:

The air in the lightning path suddenly and violently heats up, making its temperature as high as 15,000-20,000, thus causing the air to expand dramatically, and the air pressure near the channel can increase to more than 100 atmospheres. This is followed by rapid cooling, the air shrinks rapidly, and the pressure decreases. This sudden expansion and contraction occurs in a short period of a few thousandths of a second, so in the moment of the lightning explosion, a shock wave is generated.

The shock wave travels in all directions at a speed of 5,000 meters per second, and during propagation, its energy quickly decays, while the wavelength gradually increases. Seconds after the lightning strikes, the shock wave evolves into a sound wave, which is what we hear as thunder.

The reason why lightning is seen first and then thunder is heard is that light travels much faster than sound.

In thunderclouds, lightning and thunder occur at the same time. When lightning, the temperature in the convective cloud can reach about 1000, the gas will expand rapidly, the cloud droplets and rain will vaporize sharply, and the lightning will cool down quickly, and the air will produce a huge thunder when it vibrates strongly. The reason why people always see lightning and hear thunder later is because light travels much faster than sound.

According to the propagation velocity, the propagation speed of sound in the air is 340 meters per second; The speed of light waves in the air is 300,000 kilometers per second. It can be seen that the speed of light waves in the air is much greater than that of sound. So we see lightning first, and then we hear thunder.

Sometimes the thunder drags on for a long time, due to the reflection of the thunder back and forth from clouds, mountain peaks and the ground.

Similarities and differences between sound and light

Sound and light are both waves, that is, they both have the characteristics of waves, such as refraction, reflection, diffraction, interference, polarization, Doppler effect, standing waves, resonance, etc. In addition, there are many similarities between the mathematical expressions that describe the wave function and the methods used to study waves. The above are the similarities between the two.

The difference between them is that sound is a mechanical wave, it needs to have a vibration source and a medium, sound is the propagation of mechanical vibration in the medium, the frequency of sound is related to the vibration source, the wave speed of sound is related to the medium, the sound wave source stops vibrating, the sound stops propagating, and there will be no sound in a vacuum. Light waves are electromagnetic waves, and their frequency is excited by the changing electric field, which in turn excites the changing electric field, propagating in space.

The above content refers to Encyclopedia - Lightning.

Encyclopedia - Thunder.