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Chapter 1 Introduction to Electricity Section 1 Electric Charge and Static Electricity Notes Electric Charge • • All matter composed of very small particles atoms Atoms made of even smaller particles: o Proton – charged o Electron – charged o Neutron – not charged Charges Exert Forces o Charge is a physical property. o Objects can have: Positive charge Negative charge Neutral charge o Charged objects exert a force – a push or a pull o Law of electric charges states that like charges repel, or push away and opposite charges attract – just like magnets! The Force Between Protons and Electrons o Protons positive charge o Electrons negative charge o Neutrons neutral charge Protons and neutrons attracted to each other! The Electric Force and the Electric Field o The force between charged objects electric force o Electric force depends on two things: Amount of charge on each object Greater the charge – the greater the electric force Distance between the charges the closer the charges are – the greater the electric force is Charged objects affected by electric force because of an electric field around them. Electric field – the space around a charged object in which another charged object experiences an electric force. Objects in this field can be attracted or repelled depending on their own charge. Charge It! o o o o All atoms have equal numbers of protons and electron resulting in No Charge! Objects become positively charged when lose an electron Objects become negatively charged when gain an electron Objects can also become charged through: Friction – when electron are “wiped” from one object onto another. Conduction – when electrons move from one object to another by direct contact. Induction – when charges in an uncharged metal object are rearranged without direct contact with a charged object. o Conservation of Charge When you change the charge of something by any means no charges are created or destroyed Amount of electrons and protons stay the same – they simply move. Because of the move it is said that the charge is conserved o Detecting Charge Electroscope – used to see if something is charged Constructed from: glass flask, metal rod, rubber stopper, and metal leaves When the electroscope is not charged the leaves hang straight When the electroscope is charged the leaves spread apart or repel Moving Charge o Most materials are either conductors or insulators based on how material move through them o Conductor Electrical conductor – a material in which charges can move easily Examples: metals such as copper, aluminum, and mercury o Insulators Electrical insulators – a material in which charges cannot move easily because electrons cannot move freely Examples: plastic, rubber, glass, wood, and air Static Electricity o Static electricity – the electric charge at rest on an object When something is static it not moving or changing – the charges of static electricity do not leave the object – they stay charged. Example: Clothes in the dryer Clothes charged from friction Negative charges from some clothing transfer to other clothing Dryer stops – the transfer of charges stop Clothing an insulator so the clothing retains the electric charge build up – RESULT static cling! Electric Discharge o When static electricity eventually leaves is called – electric discharge o Electric discharge – loss of static electricity as charges move off an object o This process can happen slow or fast Quickly: Flash of light Shock Crackling noise Lightening Lightning Dangers o Strikes at the highest point in a charged area because it is the shortest path o How lightning forms: Negative charges build up in a cloud because of water and air in the cloud Different parts of the cloud have different charges top of the cloud positive charges bottom of cloud negative charges The negative charges at the bottom of the cloud react with the positive charges on Earth’s surface Most lightning happens within and between clouds Lightning Rods o Mounted so they are the tallest point on a building A pointed rod connected to the ground by a wire by connecting it to the ground through a wire it is grounded Any object that is grounded provides a path for the electrical charge to move to Earth Earth can absorb the electrical charges without causing damage o They prevent the buildings from being damaged by lightning