Posts tagged ‘lightning’

Calculating the Distance to Lightning Strikes

By Chad Upton | Editor

I love watching electrical storms. The time between strikes builds anticipation; the light show is epic and the sound is awe inspiring.

As a kid, I heard that if you count the seconds between the sight of the lightning and the sound of the thunder, the distance to the strike is one mile for every second you count. It’s a simple model, but it’s far from accurate.

It’s actually closer to 5 seconds for every mile.

For those who don’t know, you see the lightning before you hear the thunder because light travels much faster than sound, about 200,000 km per second faster (186,282 miles per second).

Depending on the environment, sound travels at about 350 meters per second (1150 feet per second). To calculate the distance, you can multiply the number of seconds by the speed of sound in your preferred units above.

If you count 10 seconds between the lightning and the thunder, the strike was about 3.5 km (2.17 miles away). To make it easier, use this lightning distance calculator.

Thanks to Kristen for this suggestion.

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Image: John Fowler (cc)

Sources: Lightning Strike Distance Calculator, Wikipedia (Speed of Light, Speed of Sound)

June 21, 2011 at 2:00 am 8 comments

Tires Do Not Protect You During a Vehicle Lightning Strike

By Chad Upton

I’ve always heard that a car is one of the safest places to be during a lightning strike and that is true.

The tires usually get all the credit. As the story goes, tires are rubber and rubber is an insulator, so you don’t get electrocuted in the car because you’re isolated from the ground like a bird on a wire.

It’s a pretty believable story, but it’s not the truth.

If you think about it, the lightning travels thousands of feet through thin air to reach the car — it could easily continue to travel through thin air to get around a few inches of rubber tires. Compared to the power of lightning, tires don’t really provide any protection.

Trains are struck by lightning and the people inside are fine, even though trains have metal wheels, which are great conductors.

Airplanes are regularly struck by lightning in the air. In fact, the FAA estimates that each plane gets struck about once per year.

So why are people safe in these cases?

It’s all because of a principle discovered by Michael Faraday in 1836.

Faraday demonstrated that an electrical charge exists only on the exterior of a hollow conductor and not the interior. He built a wire cage, that is now know as a Faraday cage, to demonstrate that an electrical current flowing through the cage did not produce an electrical current inside the cage.  When you’re in a vehicle, with a conductive exterior shell, you’re inside a Faraday cage and the electrical charge is carried around you.

Faraday cages can also be used to shield against electromagnetic radiation. Coaxial cables are common in most households for carrying TV signals. These cables are design with what amounts to be a built in Faraday cage to protect the inner copper wire from electrical noise.

Microwave ovens are also a good example of a Faraday cage. This principle protects you from exposure to microwaves by turning the inside of the oven into a Faraday cage. The mesh you see on the inside of the door is part of that cage and explains why the glass isn’t perfectly transparent.

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Sources: Wikipedia (Ground, Faraday Cage), Weather Imagery (Cars, Airplanes), Faraday Cage

Photo: jonathan mcintosh (cc)

July 21, 2010 at 5:00 am 18 comments


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