Faraday cage

Electricity is very helpful to our lives. It lights up light bulbs and power many devices. However, electricity can also be harmful. As many people know, exposure under high voltage of electricity can be lethal. We have definitely learned how dangerous electricity can be from the cases that people died or severely injured by electric shock. Moms don't tell us to keep our hands away from plugs for no reason. I think most of the people will agree that standing near a place that has a high electric voltage is definitely not a good idea. However, what if I tell you that you can be completely safe when you stand by a device that generates a high electric voltage. You may think I am crazy. Nevertheless, what I just said is totally achievable, and it is all thanks to the law of physics.

When we talk about electricity, there are two types of material have to be brought up, insulator and conductor. Insulators are the materials that do not have free charges. Charges are not able to move freely inside them. Conductors, on the other hand, allows charges to move freely inside the material. This property of conductors makes them behave in a certain way in the presence of electric field. When there's an electric field near a conductor, the electric field polarizes the conductor, which causes positive charges and negative charges move to two different ends. When the conductor is polarized, there will be another electric field inside the conductor. This electric field has the same magnitude but opposite direction to the external electric field. This induced electric field then cancels out the external electric field, so there's no electric field inside the conductor. When you take a hollow conductor and introduce an external electric field, you will find that there will be no electric field inside the shell.
   
That is to say, even in the presence of a strong electric field, there's still no electric field inside the hollow conductor. The object inside the conductor remains unaffected by the external field. This property has been tested countless of times. In some demonstration, you can see people stand in the cage that is placed beside a device that generates a high voltage when the device is turned on, the people inside the cage remains unharmed because there's no electric field inside the cage. Actually, we can see faraday cages almost every day. Cars on the roads are faraday cages, The metal shell of the cars are conductors, so the electric field inside the car is always zero if there's no net charge inside the car. That is to say, if a lightning strikes a car, the people inside the car will not be harmed because the external electric field does not affect the object inside the conductor shell. Faraday cages are also applied in many places. It can be used to protect sensitive devices or information transmitting wires.

Law of physics is always interesting. When we understand it, we can use it in many different ways.  After reading this article, I am sure that you know what to do when the lightning strikes. Remember, stay in the car.