# Electric Charge and Static Electricity. Electric Charge  All matter is made up of atoms  Atoms contain 1. Protons (+) 2. Neutrons (0) 3. Electrons (-)

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Electric Charge and Static Electricity

Electric Charge  All matter is made up of atoms  Atoms contain 1. Protons (+) 2. Neutrons (0) 3. Electrons (-)

What is Static Electricity?  Static electricity occurs when there is a build up of electric charge on the surface of a material.  It is called static electricity because the charges don’t move.  The electricity we use everyday involves moving charges.

What is charge?  To understand charge we have to look at things on an extremely small scale.  We have to try and understand things that we can’t even see with the most powerful microscope. Atoms!

The atom  Everything we see around us everyday is made of atoms.  We can’t see individual atoms because they are so small.  In fact the diameter of an atom is about 0.0000000001m  In the air in your classroom there are about 1500000000000000000000000000 atoms.

What is inside the atom?  The atom is made of 3 sorts of particles. The electron The proton The neutron  We can imagine each as a tiny little ball.

Inside an atom  The protons and neutrons sit together in a lump in the middle called the nucleus.  The electrons orbit around the nucleus, a bit like the planets orbiting the Sun. Most of the atom is empty space if atoms were the size of football fields, the nucleus would be a grain of sand in the middle and the electrons would be orbiting around the edge..

Charge  The electron is negatively charged.  The proton is positively charged.  The neutron has no charge, it is neutral.

Charge  Most things have the same number of electrons and protons in them.  They don’t have any overall charge.  If this isn’t true interesting things can happen.

How do charges behave?  What do you know about magnets?  2 north poles will repel each other, but a north and a south put together will attract one another. opposites attract, likes repel.

How do charges behave?  Exactly the same thing happens with charges.  2 positive charges put together will repel each other.  Put a positive charge near a negative charge and they will attract each other.  A charged object may even attract a neutral one. WHY?

Law of Electric Charges  The law of electric charges states that like charges repel, and opposite charges attract.  Protons are positively charged and electrons are negatively charged, so they are attracted to each other.  Without this attraction, electrons would not be held in atoms.

Recall This? The Fundamental Forces  The strong nuclear interaction is very strong, but very short-ranged. It acts only over ranges of order 10-13 centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances.  The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long-ranged, but much weaker than the strong force. It can be attractive or repulsive, and acts only between pieces of matter carrying electrical charge.  The weak nuclear force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak.  The gravitational force is weak, but very long ranged. Furthermore, it is always attractive, and acts between any two pieces of matter in the Universe since mass is its source.

How bout This? The Fundamental Forces  The strong nuclear interaction is very strong, but very short-ranged. It acts only over ranges of order 10-13 centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances.  The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long- ranged, but much weaker than the strong force. It can be attractive or repulsive, and acts only between pieces of matter carrying electrical charge.  The weak nuclear force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak.  The gravitational force is weak, but very long ranged. Furthermore, it is always attractive, and acts between any two pieces of matter in the Universe since mass is its source.

What is Static Electricity? Law of Electric Charges: 1. Opposite charges attract

What is Static Electricity? Law of Electric Charges: 1. Opposite charges attract 2. Like charges repel

What is Static Electricity? Law of Electric Charges: 1. Opposite charges attract 2. Like charges repel 3. Charged objects attract neutral objects

Law of Electric Charges

What?

Electric Force The force between the charged objects is an electric force. The size of the electric force depends on 2 things: 1. The amount of charge (the greater the charge, the greater the force) 2. The distance between charges (the further the distance, the less the force) Talk more about this later…

Electric Field  An electric field is the region around a charged object where electric forces can be exerted on another charged object. (Repelled or attracted) Talk more about this later…

Charged Objects  Atoms do not have a charge because the number of electrons and protons cancel each other out. Ex. 3 protons (+) & 3 electrons (-) = 0

Charged Objects How do objects get charged?  They either gain or lose electrons.  Why not protons? Ex. 3 protons (+) & 5 electrons (-) = 7 protons (+) & 2 electrons (-) =

What is Static Electricity? We don't draw atoms, just "+" and "–" to illustrate the overall charges e.g. a neutral object 5 + 5 - overall charge0

What is Static Electricity? We don't draw atoms, just "+" and "–" to illustrate the overall charges e.g. a positive object 5 + 3 - overall charge2+

What is Static Electricity? We don't draw atoms, just "+" and "–" to illustrate the overall charges e.g. a negative object 5 + 8 - overall charge3 -

Hi!

How Can You Charge Objects?  There are 3 ways objects can be charged:  Can you name them? 1. Friction 2. Conduction 3. Induction **In each of these, only the electrons move. The protons stay in the nucleus**

Static electricity  It is this imbalance of positive and negative charges that causes:  Balloons to stick to walls.  Your hair to stand on end when brush your hair on a dry day.  And the electric shock you sometimes get from the door handle.

Friction  Charging by friction occurs when electrons are “wiped” from one object onto another. Ex. If you use a cloth to rub a plastic ruler, electrons move from the cloth to the ruler. The ruler gains electrons and the cloth loses electrons.

Static electricity  Static electricity is caused when certain materials are rubbed against each other.  Electrons can be rubbed off one material and on to another.  The material that has got extra electrons is now negatively charged  The material which has lost electrons is positively charged.

+ + + + + + + + + + - - - - - - -- - -

+ + + + + + + + + + - - - - - - -- - -

+ + + + + + + + + + - - - - - - -- - -

+ + + + + + + + + + - - - - - - -- - -

+ + + + + + + + + + - - - - - - -- - -

+ + + + ++ - - - - - - -- - - + ++ +

Conduction  Charging by conduction happens when electrons move from one object to another through direct contact (touching). Ex. Suppose you touch an uncharged piece of metal with a positively charged glass rod. Electrons from the metal will move to the glass rod. The metal loses electrons and becomes positively charged.

Induction  Charging by induction happens when charges in an uncharged object are rearranged without direct contact with a charged object. Ex. If you charge up a balloon through friction and place the balloon near pieces of paper, the charges of the paper will be rearranged and the paper will be attracted to the balloon.

Conservation of Charge  When you charge something by any method, no charges are created or destroyed.  The numbers of electrons and protons stay the same. Electrons simply move from one atom to another, which makes areas that have different charges.

Conductors and Insulators  An electrical conductor is a material in which charges can move easily.  Most metals are good conductors because some of their electrons are free to move.  Conductors are used to make wires. For example, a lamp cord has metal wire and metal prongs.  Copper, aluminum, and mercury are good conductors.

Conductors and Insulators  An electrical insulator is a material in which charges cannot move easily.  Insulators do not conduct charges very well because their electrons cannot flow freely. The electrons are tightly held in the atoms of the insulator.  The insulating material in a lamp cord stops charges from leaving the wire and protects you from electric shock.  Plastic, rubber, glass, wood, and air are good insulators.

Static Electricity  Static electricity is the electric charge at rest on an object.  When something is static, it is not moving.  The charges of static electricity do not move away from the object that they are in. So, the object keeps its charge.  Ex. Clothes taken out of a dryer

Electric Discharge  The loss of static electricity as charges move off an object is called electric discharge. Sometimes, electric discharge happens slowly. Ex: static on clothes Sometimes, electric discharge happens quickly. Ex. wearing rubber-soled shoes on carpet, lightning

Lightning

What causes lightning?  Lightning is actually just static electricity on a much larger scale.  The rubbing is caused by air moving around  In thunderclouds bottom is usually negative and top is positive.

Thunder  When the lightning flash happens it heats the air to a temperature 5 times hotter than the surface of the sun.  This causes nearby air to expand and vibrate forming the sound we hear as thunder.

Interesting facts  Lightning bolts can travel at speeds of up to 60,000 miles per second.  Every second around 100 bolts of lightning strike the Earth.  One lightning bolt has enough electricity to power 200,000 homes.  You are more likely to be struck by lightning than be eaten by a shark.

Some myths  Lightning never strikes in the same place twice.  False, the Empire State Building is reportedly struck 100 times a year.  Wearing rubber shoes will protect me in a thunder storm.  False, Lighting is too powerful to be stopped by half an inch of rubber or several hundred feet of rubber for that matter.

How Lightning Forms

Lightning  Lightning usually strikes the highest point in a charged area because that point provides the shortest path for the charges to reach the ground.  Anything that sticks up or out in an area can provide a path for lightning.  A lightning rod is a pointed rod connected to the ground by a wire.  Objects, such as a lightning rod, that are joined to Earth by a conductor, such as a wire, are “grounded.” Any object that is grounded provides a path for electric charges to move to Earth.  Because Earth is so large, it can give up or absorb charges without being damaged.  When lightning strikes a lightning rod, the electric charges are carried safely to Earth through the rod’s wire. By directing the charge to Earth, the rods prevent lightning from damaging buildings.

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