Electric Discharge Grounding and Lightning

Learning Goals By the end of this class you should be able to:  Differentiate between the different methods of discharging an object.  Understand how and why lightning occurs.

Discharging Electrically Charged Objects discharged or neutralized If a charged object has all the excess electric charge removed, it is said to be discharged or neutralized. Ways to Discharge Objects: – Grounding – Discharge at a point – Exposure to the air (moist air) – Expose it to radioactivity (electrons are taken) – Shine a light on it

Grounding an Object Connect a charged object to Earth through a conductor. The charged object will share its charge with the entire Earth. Damp soil is a fairly good conductor but the Earth removes the excess charge.

Grounding an Object Electrical Ground

Discharge at a Point The shape of a charged conductor affects the rate at which it becomes discharged Smooth, spherical shapes retain charges indefinitely, because the charges spread themselves evenly over the surface Smooth, spherical shapes retain charges indefinitely, because the charges spread themselves evenly over the surface Conductors pointed at the ends lose charges rapidly because electrons repel one another so strongly that those right at the tip are actually pushed off the point discharge at a point This is called discharge at a point

Discharge at a Point Static wicks on airplanes

Lightning Electric charges, mostly negatively charged electrons, are continuously being removed from Earth’s surface by a variety of processes. Lightning appears to be a jagged path of white light moving toward the ground. Lightning appears to be a jagged path of white light moving toward the ground. This path is sometimes created by traces of moisture in the air, or by a concentration of positive ions. How Lightning Forms Lightning Strikes Explained What is Lightning Slow Motion Lightning –Web video Slow Motion LightningWeb video Upward Lightning

Lightning!

Sprites

Lightning Rods A pointed metal rod is attached to the highest part of the building. A thick conductor, usually copper, is connected from the pointed rod to a metal plate buried in the ground. A thick conductor, usually copper, is connected from the pointed rod to a metal plate buried in the ground. Provides 2 kinds of protection: – Helps prevent lightning from striking – Directs the charge through the conductor to the ground

Lightning Rods Lightning rods are positively charged. This does two things: 1. attracts lightning to strike the rod and not the house, or 2. collects enough negatively charged particles around it so as to divert lighting away from your house.

Why are open areas dangerous during a thunderstorm? – They are dangerous because you tend to be the tallest object and lightning would be attracted to you. – Golfers & Soccer Players! Be careful!

How would you minimize the risk of being hit on land or water? - On land, you’d want to get down low, by lying down or crouching on the ground or in a ditch. - On water, you’d want to return to land as fast as you can. - Or Stand next to a tall person

Class/Homework Pg. 495 # 1,2,5