Static Electricity Ms Petrauskas Static Electricity An imbalance

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Static Electricity Ms. Petrauskas

Static Electricity �An imbalance of electric charge on the surface of an object �Static means stationary or non-moving

Electric charge �A form of charge either positive or negative that exerts an electric force • Ex. When an atom is not neutral �A ‘+’ symbol represents a large number of protons an a ‘-’ symbol represents a large number of electrons �Shows the distribution of charges in an object

Law of Electric Charges �Like charges repel + �Opposites + attract + �Any charge attracts neutral +- + -

Laws continued �The strength of the electric force is directly related to the strength of the charges on each object �Decreases with distance between objects

Pithball electroscope �Detects �Pithball charge is neutral and if the object is charged then the pithball will be attracted to it.

Neutral Attraction �As a charged object is brought close to a neutral object it causes (induces) a rearranging of electrons �Inducing a movement of electrons is called induced charge separation Charge not permanent!

Metal Leaf Electroscope �More sensitive than pith ball when detecting electrical charge �When a charge is transferred (by contact or by induction) the leaves receive the same charge and therefore repel each other

Charging by friction �When two objects of different materials rub against each other, they produce a net static charge

Electrostatic Charges �One material has a stronger attraction to electrons than another material, and therefore pulls those electrons away resulting in a negative charge �The material that loses electrons becomes positively charged �Most object are electrically neutral

Electrostatic Series �A list of materials arranged by their likelihood to attract electrons �Used to predict resulting charges from contact

Examples: see page 473 �What is the resulting charge when ebonite and rabbit fur are rubbed together? �Nylon �Which and wool? would have a stronger resulting charge?

Insulators and Conductors � Insulator: electrons do not move freely between atoms in this material • Wood, rubber, wax � Conductor: electrons move freely from atom to atom in this material • Metal, tap water � Semi- conducter: electrons can move fairly well in these non-metal materials • Silicone, mixtures of arsenic, selenium and tellurium

Charging by Contact � Aka charging by conduction � When two objects with different amounts of charge come into contact and electrons move from one object to another �“ electrons distribute” � The neutral object takes the charge of the charged object � SO when a + touches a neutral object the object become + and when - touches neutral it becomes -

Negatively charged Neutral Object becomes negative

Positive Neutral becomes positive

Grounding Removing a net static charge by putting it into contact with the ground �Has a large number of electrons and can either supply or remove �Earth is so huge, it can do this without affecting its overall charge �

Grounding = Neutralizes Electrons move up to neutralize Electrons move toward the earth

Shocks & Sparks � When a large number of electrons flow rapidly between objects (more often with a conductor) � Ex. When wearing cotton socks and you walk across a polyester carpet and then touch a doorknob= SHOCK!. • What charge do your socks become? Positive • When you touch a conductor like a doorknob, electrons quickly flow into you, to neutralize your charge, causing a shock or spark � Avoid by slowly releasing electrons with a insulator “ground” � Grounding is used in the following situations • • Operating rooms Fuel trucks Lightning Appliances

Applications �Dryer sheets • waxy coating equals charges so there is no transfer of electrons, no static �Higher humidity • more water in air and charges removed quickly through collisions because of the close proximity with water vapour �Grounding electronics • Third prong is a ground. Shocks and sparks can damage equipment and/or cause fires

�Precipitator- remove pollution particles from air in power plants. Particles pass by negatively charged plates and become negative by contact. They then pass positive plates and stick. �Electrostatic duster- sweep across the ground, creates a build-up of charge, dust “jumps” from dusty surface to duster