PowerPoint Presentation

Objectives: 1. Identify two forces that result from electric charges2. Explain why objects attract and repel each other.3. Communicate how positively charged object can be used to determine the charge on another object.4. Infer how electric charges behave in everyday situationsElectricity

Review concerning Charge and ForceRecall that matter is made of atoms which containelectrons, protons and neutrons. PROTONS - ELECTRONS NEUTRONS + charge chargeNO chargeWhat do charged particles create?The positive and negative electric charges inobjects can produce a force between the objects. If charges are opposite, they will cause objects to attract to each other. If charges are alike the will cause objects to repel or push away from each other.FORCE OF ATTRACTION + Opposites attract

FORCE OF REPULSION--Like charges will repel each other

ELECTRIC FIELDAn electric field is a region surrounding a charged object.

Strongest part offield is closest tothe charged areaWeakest part of field Is the area farthest away from the charged objectPerhaps you have experienced this. When you driveclose to a power line you may get some static on a carradio. What causes this?

Because there is an electric current flowing throughthe power line there is an electric field around theline. This electric field can cause interference on your radio.Power lineELECTRICITY AND YOU

Your body uses electric signals to communicate with the brain.If you touch something hot, the - charge inside the nerve cellchanges sending a signal along the nerve cell to the spinal cord, to your hand, telling it to drop the object.11.2 STATIC ELECTRICITYObjectives:1. Identify three ways static charge can build up2. Explain what causes lightning.3. Compare electric conductors and insulators4. Infer why lightning can be dangerous

Has this ever happened to you?

How does the person who shocked you becomecharged with electricity? First of all, you must understand that of the threeParticles that make up an atom, ONLY THE e CANMOVE.When the person who shocked you rubbed theirfeet on the carpet electrons from the carpet weremoved to the person. This build up of electrons jumped from their finger to your ear.Static build-up is when electrons become overloadedon an object. Static means stationary or not moving.In this example the person (object) became charged by

FRICTIONCan you think of other examples of causing static build-up (charging) by friction? CONDUCTION Charging by conduction occurs when electrons are transferred from one material to another by direct contact

---- -- ------- -------When the leaves of the electro-scope become loaded with electronsthey repel and separate.electroscopea device which detects an electrical chargeINDUCTIONCharging by induction occurs when charges are rearranged without direct contact, the charged object simple comes close to another object.

- - - --- ------- --------electroscopeWhat has become charged?The leaves of the electroscope- - - - -

LIGHTNING

HOW DOES IT HAPPEN ?

+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_++_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+When clouds are swirled around and blown together byturbulence in the upper atmosphere, there is a great deal of friction between the water molecules. This frictioncauses electrons to be jarred loose and eventually thereis a build-up of electrons within an area of the cloud.This is called static build-up. When this happens,lightning can occur in several ways: ++++++++++++++++++++++++++++++++++++_ _ _ _ _ __ _ __ _ __ _ +_ _ _+ _ _ ++ _ _ _ _ + _ _ __ _ + _ _ _ + _ __ _ + _ _ _ _ One end of the cloud has more+ charges.The other end of thecloud has more charges.What happens now?+ _ + _ + _ + _ + _ + _ + _+ _ + _ + _ + _ + _ + _ + _+_ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ The + - attraction betweenthe ends of the clouds causesa static discharge(lightning) resulting in a cloud which nowhas evenly distributed + & - charges.Lightning within a singlecloud is calledSt. Elmos FireThe most common form of lightning+ + + _ ++ _ + + __ + + + + _ _ _ + __ + _ _ _ ++ _ _ _ _+ + + _ ++ _ + + __ + + + + _ _ _ + __ + _ _ _ ++ _ _ _ _What will happen here?A charged cloud+ _A second charged cloud+ _Where is the + - attraction?When the negative end of one cloud comes close to the positive end on another cloud you will see lightning from one cloud to another.+ _ + _ + _ + _ + _ + _ + _ + _ + _ + _ +_+ + + _ ++ _ + + __ + + + + _ _ _ + __ + _ _ _ ++ _ _ _ _+ _How does one cloud charge another?A charged cloudA neutral cloud+ _ + + +_ + _ + ++ + + + __ _ + _ __ + _ _ +_ _ _ + When a charged object comes close to another object, thesecond object becomes charged by __________________.INDUCTIONWhat makes this happen?Like charges repel so when the end with a large number ofelectrons (-) comes close to the other cloud the electronsin the neutral cloud are repelled to the other end of thecloud causing it to have charged ends.+ _How does lightning strike things on the ground?

+ + + _ ++ _ + + +_ + _ _ _ +_ _ _ _ A neutraltree with+ & - scatteredequally throughoutA charged cloudWhat happens?+ + + + _+ + _ + + _ __ __ +When the cloud gets close tothe tree the tree becomes chargedby induction. When the + / -attraction becomes great enough there is a static discharge of electrons to the tree.

+ + + _ ++ _ + + +_ + _ _ _ +_ _ _ _ A charged cloudWhy is it unsafe to seek shelter under a tree during a storm?

+ + + _ + ++ + + _ ++ +____+ _+ _+ _Lightning will try to find the fastest way to the ground. Thepeople under the tree becomecharged by induction just likethe tree does. As lightning takes its path to the ground, it will come out of the tree and to the boys then to the ground.

LIGHTNINGWILL KILL YOU DEAD!

Dont make someone cry.VSCONDUCTORSINSULATORSCONDUCTORS - A material through which electric charges flow easily.Examples include most metals such as gold, silver, copper,aluminum and mercury. Non metals such as water and acidare also good conductors.NOTE: Pure water does not conduct electricity, it musthave some type of electrolyte or substance in it. Since thewater you use at home is not pure water, it is a good conductor, it is wise to be careful when handling appliances around wet areas.INSULATORS: Materials through which electric charges cannot move easily.Examples include wood, ceramic, rubber, glass and plastic.Note: you may have noticed that most wire to electrical appliances are coated with rubber or plastic.wireinsulationIn an insulator, the atoms are not arranged in a manner which will allow the electrons to move freely. Therefore,insulators are not capable of carrying electrical energy.SCIENCE AND YOUDo your clothes ever stick together when you take them of the dryer?Does your hair follow the comb or brush instead of lying flat?While drying, some clothes pick up a negative charge while others keep a positive charge. Using your knowledge about charges what happens?Using your knowledge about charges, explain what you think happens to your hair.