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LIGHTNING ROD
------ Interactive Physics Simulation ------
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Why do buildings have lightning rods?
Static charge builds up in clouds due to frictional charging of water molecules. Charge separation occurs within the cloud, inducing positive charge at the ground level. If sufficient charge builds up, a strong electric field is created. This field is strong enough to strip electrons from the air molecules, making it a conducting plasma. Once a conducting path between the cloud and the ground is created, charge flows rapidly - a lightning strike! The electric potential, or voltage, of the cloud and the ground are very different. The electric field is strongest where the electric potential is changing most quickly. A lightning rod draws lightning to it by allowing a very strong electric field to form.
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Cloud Height - This slider adjusts the height of the cloud. Electric sparks wi ll only flow through air if the electric field is high enough. Electric field strength is proportional to the voltage difference and inversely proportional to the distance between two objects. In other words, to get a strong electric field, bring two charged objects very close together. Lower clouds, then, with high charge separations, will be more likely to generate a lightning bolt.
Overlay - This slider allows you to overlay different physics concepts on top of the picture. The equipotentials show all the points at the same potential (voltage). High voltage regions can be found near positive charges; low voltage regions are found near negative charges. Positive charges tend to flow from high to low voltage, and negative charges flow in the opposite direction. The electric fields show the direction and magnitude (per unit charge) of the electric force a positive charge would feel if placed at that location. (Negative charges feel a force in the opposite direction). If you overlay both you can see that electric fields point .
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Charge Separation - This slider allows you to control how much charge separation ha s occurred in the cloud. Just as rubbing your feet on a carpet can generate a separation of charge, clouds passing by one another and rubbing (via wind) can generate a charge imbalance. Higher charge imbalances are more likely to create lightning discharges.
Lightning Rod - A lightning rod is a piece of metal at the top of a tall build ing that guides lightning strikes directly down into the Earth so they don't damage the building directly.
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If the cloud height is 14 km, what charge separation in the cloud will produce a bolt of lightning? (Adjust the charge separation slider and press play until lightning strikes.)
If the cloud height is 2 km, what minimum charge separation in the cloud will produce a bolt of lightning? (Adjust the charge separation slider and press play until ligh tning strikes.)
Adjust the sliders to maximize the strength of the electric field. (Lower clouds and higher charge separation are more likely to produce a bolt of lightning.)
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Challenge ME!
Have you ever received an electric shock when walking on a carpet?
Have you ever rubbed a balloon on your hair and created an electric charge?
Need Help?
Check out the Lightning Rod Walkthrough video at: https://youtu.be/PaFeNFVbZOs
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Is an ordinary electric shock like lightning ? When you rub your shoes on the carpet and touch a doorknob, you sometimes get an electric shock. This phenomenon is, indeed, very much like lightning: when an imbalance in electric charge is created through rubbing (whether it is shoes-on-carpet, or cloud-on-cloud), electric fields are generated. The more charge, the stronger the field. When the field is strong enough to ionize the molecules in the air (basically, rip electrons out of them), the air becomes temporarily conducting, like a wire. We see a flash of charge pass through this temporary path. Once the excess charge has balanced itself out, the path goes away, and things are back to "neutral".
Does a lightning bolt involve a lot of charge ? There is no question that there is a lot of power in a lightning strike. Billions of Joules of energy are transferred in less than a second. But the voltage separation between the cloud and the ground is also high, which means that each bit of charge has huge potential energy. Relatively small amounts of charge - tens of Coulombs - are actually transferring when a lightning bolt strikes!
Does lightning always produce thunder ? Thunder is the sound produced by the lightning strike. Because the light from a lightning bolt travels to your eye very rapidly (at the speed of light!) but the sound travels more slowly (at the speed of sound), the two might seem to be separate phenomena.
What was Benjamin Franklin up to? Benjamin Franklin is most famous as a statesman and politician, but he also made important contributions to science. Most famously, he confirmed through a very dangerous experiment that lightning is in fact an electrical phenomenon. He flew a kite high in the sky - higher than any convenient building of the time - and the lightning strike produced an electric shock he could witness first-hand.
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Physics Concepts | Click on the link below to learn more.
Electrostatics - http://www.ck12.org/physics/Electrostatics
Electric Fields - http://www.ck12.org/physics/Electric-Fields
Electric Field Intensity - http://www.ck12.org/physics/Electric-Field-Intensity
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